Additional Geologic Mapping Notes

8/3/2019 Additional Geologic Mapping Notes

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UNIVERSAL TRANSVERSE MERCATOR COORDINATE SYSTEM (UTM)

Standing at the road junction marked with the star on the topographic map pictured above, a GPS unit set to displayposition in UTM coordinates, would report a location of:

10 S 05597414282182

The 10 S represents the zone you are in. The zone is necessary to make the coordinates unique over the entire globe.


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The top set of numbers, 0559741, represent a measurement of East-West position, within the zone, in meters. It'scalled an easting.

The bottom set of numbers, 4282182, represent a measurement of North-South position, within the zone, in meters.It's called a northing.

The map has Universal Transverse Mercator (UTM) grid lines spaced every kilometer or 1000 meters. The verticalgrid lines determine East-West position and the horizontal grid lines determine North-South position.

Look along the bottom edge of the map at the labels for the vertical grid lines.

559 and 560000 mE.

The label, 560000 mE., reads "five hundred and sixty thousand meters East." The label, 559, is an abbreviation for,559000 mE. The two grid lines are 1000 meters apart. The horizontal grid lines are labeled in a similar manner.

Most land navigation activities focus on a very small portion of the globe at any one time. Typically the area ofinterest to an outdoorsman is less than 20 miles on a side. This focus on a small area allows us to abbreviate UTMcoordinates.

The zone information and the digits representing 1,000,000m, and 100,000m are dropped. The 1m, 10m and 100mdigits are used only to the extent of accuracy desired.

A GPS unit might read10 S 0559741

4282182

Using a notation similar to the one found on a USGS topographic map, this would be written as:

Zone 10 S 559741 mE. 4282182 mN.

An abbreviated format for the same coordinates would look like:

59 82 Describes a 1000m by 1000m square.




The 100m abbreviated format, 597 821, and the 10m abbreviated format,5974 8218, are the most commonly used.

Notice that the easting is reported first, followed by the northing. Remember the phrase "read right up" to help youremember to read the easting from left to right, followed by the northing from the bottom up.

Also notice that when you abbreviate coordinates you should not do any rounding.0559651 becomes 596 not 597.This ensures that your position is still within the reported square. As accuracy decreases, the square gets bigger.


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SEISMIC REFLECTION PROFILES

Seismic reflection profiling involves the measurement of the two-way travel time of seismic waves transmitted fromsurface and reflected back to the surface at the interfaces between contrasting geological layers. Reflection of thetransmitted energy will only occur when there is a contrast in the acoustic impedance (product of the seismicvelocity and density) between these layers. The strength of the contrast in the acoustic impedance of the two layers

determines the amplitude of the reflected signal. The reflected signal is detected on surface using an array of highfrequency geophones (typically 48-96). As with seismic refraction, the seismic energy is provided by a 'shot' onsurface. For shallow applications this will normally comprise a hammer and plate, weight drop or explosive charge.In most reflection surveys shots are deployed at a number of different positions in relation to the geophone array inorder to obtain reflections from the same point on the interface at different geophones in the array. Each commonpoint of reflection is termed a common mid-point (CMP) and the number of times each one is sampled determinesthe 'fold coverage' for the survey. Traces relating to the same CMP are stacked together to increase the signal-to-noise ratio of the survey before being combined with other CMP's stacked traces to produce a reflection profile. Inorder to stack related CMP traces a stacking velocity is applied to each trace. This accounts for the difference intwo-way travel time between the normal incidence reflection (vertical travel path below the shot) and those atincreasing offsets from the shot (known as the normal moveout or NMO). The stacking velocity will vary down thetrace to take account of the increase in velocity with depth for each reflection event.

The simplest form of seismic reflection profiling is the constant-offset method. This technique uses a singlegeophone offset from the source by a fixed distance. The two are moved along the survey line in equal steps with a

single trace being recorded at each position. The main advantage of this technique is the limited amount ofprocessing that needs to be applied to the data due to the almost vertical orientation of each raypath. However, inorder to avoid problems with interference from groundroll and the shot airwave, the offset distance has to beselected with care.

WELL LOGS

n the early 1900s, Conrad Schlumberger envisioned the concept of using electrical measurements to map subsurfaceformations; and in 1927, he and his brother Marcel performed the world's first electrical resistivity well log inFrance. (Resistivity is the measurement of the level of difficulty anelectric current has passing through a formation.)

Well logging today means anything recorded having to do with the drilling versus the depth of the well at thatmoment, many times represented by a graph and corresponding notes. Logging tools are inserted into the well tomeasure theelectrical, acoustic, radioactive and electromagnetic properties of the subsurface formations. Sometimes

the logging tools are incorporated into the drilling tool, and sometimes the drilling tools are lowered into the well atregular intervals to collect data.
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Density LogSource : Geoline Services

Engineers and drillers use well logs to measure depths of formation tops, thickness of formations, porosity, watersaturation, temperature, types of formations encountered, presence of oil and/or gas, estimated permeability,reservoir pressures and formation dip -- ultimately determining whether a well is commercially viable or not andwhether casing, cementing and completion should be run on a well. It's not only a journal of what is perforatedbelow the surface, but also a predictor of success.

Reading a Well Log

The well log includes the header, which provides specific information about the well, such as the operatingcompany, well information and type of log run; as well as the main log section, or the graph. The graph chartsvertically the depth reached, and the horizontal scale is the measurement scale, which can be represented linearlyand/or by logarithms.

Inserts are found throughout the graph at each major section of the log, identifying each curve. Curves on the log,also called traces, readings or measurements, can be represented by solid, long-dashed, short-dashed or dotted linesto decipher between the different measurements represented on the log.

The final part of the log includes the tool calibrations for before and after the log was conducted, ensuring that thelog is accurate.
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Types of Well Logs

As the technology of well logging has improved over the decades, myriad types of well logs have emerged. FromGamma Ray (GR) Logs that measure radioactivity of the rocks to determine the amount of shale in a formation toSonic (or Borehole Compensated) Logs that measure porosity by measuring how fast sound waves travel throughrocks, different tools are used to determine different subsurface characteristics.

As previously mentioned, Resistivity Logs measure how electricity travels through rocks and sediments. Thisdetermines what types of fluids are present because oil and fresh water are poor conductors of electricity, whileformation waters are salty and easily conduct electricity.

Induction Logs are used in wells that do not use mud or water, but oil-based drilling fluids or air, which arenonconductive and, therefore, cannot use electric logs. Induction uses the interaction of magnetism and electricity todetermine Resistivity.

Spontaneous Potential (SP) Logs show the permeability of the rocks in the well by calculating the electricalcurrents generated between the drilling fluids and formation water held in the pore spaces. SP is used many times todetermine between shale and sandstone.

Methods of Well Logging

Mud Logs refers to the drilling mud, or drilling fluid, used to provide buoyancy to the drill, as well as removecuttings from the well. Information from a mud logger supplements the driller's log, cuttings log and evaluation log,and is used along with logs of nearby wells to determine the commerciality of a well. Additionally, mud logsmonitor the wellbore to help prevent blowouts.

For many years, well logging tools were lowered into the well at regular intervals while drilling to retrieve data.With the advent of directional drilling, well logging had to develop to be able to log a well that was no longervertical. Logging While Drilling and Measurement-While-Drilling (or MWD) place the logging tools on the end
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of the drilling column. That way, drillers can use the information immediately to determine the direction and futureof the well.

GRAVITY SURVEYING

Introduction

Gravity surveying involves looking at the subsurface structure based on the differences in densities of the subsurfacerocks. The idea is based around a causative body - one which produces a gravity anomaly. Assessment of gravityanomalies can give ideas about depth, size and shape of the causing body. Gravity anomalies are measured in ms-2.As the anomalies are very small compared to the Earth's field (9.81ms-2), they are commonly expressed ingravityunits (g.u.), where 1 gu = 1ms-2. However, some measurements are inmilligals, where 10 milligals = 1 g.u.

Basic Theory and Measurement

The basic theory for gravity stems from Newton's Law of gravitation:

where G is the Universal Gravitational Constant (6.67x10-11m3kg-1s-2), m1 and m2 are two masses, distance rapart.

The gravitational field is best described using thegravitational potential, U:

which is a scalar (magnitude, no direction). The derivative ofUin any direction gives the component of gravity inthat direction, which gives computational flexibility.

Measurements of the gravitational field are done using a very sensitive spring and mass system (in a LaCoste &Romberg gravimeter). In this type of instrument a weight is attached to a beam and a spring (Figure 1). As gravityincreases, the weight is forced downwards, stretching the spring. Measurements are made by bringing the beam backto horizontal, the amount of movement required is proportional to the gravitational force.

Figure 1: The LaCoste-Romberg gravimeter. The original position is in bolder colours. When the gravity in creasesthe weight forces the beam to rotate. Adjusting the screw (top let) moves the beam back to horizontal. The amount

the beam moves is proportional to the gravity. Redrawn from Keary and Brooks (1991).

The spring in these gravimeters is extremely sensitive and has to be specially manufactured. Thermal effects alsohave to be accounted for my using special materials in the beam. Most gravimeters are capable of measuring achange of 0.1 g.u.

Gravity Anomalies of Simple Bodies

Consider the gravitational attraction of a point mass, m at a distance r(Figure 2). The gravitational attraction in thedirection of the mass is:


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Since only the vertical component is measured, the anomaly caused by the mass is:

This equation can now be used to build up simple geometries by integrating. For example, to build a line which isinfinite in the y-direction, integrating gives:

Integrating over the x-direction (to infinity) and then over the vertical direction between two limits will give us theanomaly of an infinite horizontal slab:

wherep is the density of the slab and tis the thickness.

Figure 2: The gravity anomaly caused by a point source mass. Redrawn from Keary and Brooks (1991)

Corrections

There are several corrections that need to be made on gravity survey results. These are:

Drift - correct for stretching in the spring by measuring a base point throughout the survey

Latitude - correct for the location of the survey due to the shape of the Earth

Elevation - correct for the height above sea-level of the survey area. This includes free air correcting for theheight (without taking into account the rocks), the Bouger correction (as free air, but takes into account therocks in the "extra" height) and the terrain correction to account for terrain away from the survey area.

Tidal - correct for the change in tides, usually using the same method as drift correction Etvs - correct for the Coriolis acceleration. For survey done using moving vehicles only

Interpretation

Interpretation can either be done using forward or inverse modeling. Forward modeling involves constructing amodel from which you calculate the gravity anomaly and then compare it to the measured anomaly. The model isthen altered until the match is acceptable. Inverse modeling uses the measured data and is inverted to providevarious parameters, such as the maximum depth, excess mass and approximate thickness.


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There is a major problem with interpretation all potential fields (magnetic, gravity and electric) in that there is nounique solution. For example if you consider the anomaly produced from a series of concentric spheres of constantmass, but differing density and radius. Each sphere acts as a point mass, each producing an identical anomaly. Thismean the model needs to be constrained in some way, perhaps using other potential techniques or existinggeological knowledge.

Limiting Depth

The limiting depth can be found using the half-width (the distance in the horizontal direction from themaximum anomaly value to the position where the anomaly is half the maximum. See Figure 2):

Other methods involve the first and second derivatives of the anomaly.Excess Mass

The excess mass is the extra mass that is occupied a body compared to the same body made of the countryrock. This involves a surface integration

Inflection PointsLocations of inflection points can give details of the bodies edge.

Approximate ThicknessIf the density contrast between the country rock and the body is known then the thickness can be estimatedusing the infinite slab formula.

Conclusion

Gravity surveying uses the difference in densities to detect subsurface anomalies. It can detect the size, shape anddepth of such an anomaly. Measurements are done with a gravimeter, typically a LaCoste-Romberg meter. Using thegravity anomaly produced by a point mass, simple structures can be built up and compared against any measuredfield anomalies. However, there are several corrections that need to be done on field measurements to remove theeffects of topography, elevation and latitude.


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GEOLOGIC TIME SCALE

RELATIVE DATING LINKED TO THE TIME SCALE

For almost the next 100 years, geologists operated using relative dating methods, both using the basicprinciples of geology and fossil succession (biostratigraphy). Various attempts were made as far back as the1700s to scientifically estimate the age of the Earth, and, later, to use this to calibrate the relative time scaleto numeric values (refer to"Changing views of the history of the Earth" by Richard Harter and ChrisStassen). Most of the early attempts were based on rates of deposition, erosion, and other geologicalprocesses, which yielded uncertain time estimates, but which clearly indicated Earth history was at least100 million or more years old. A challenge to this interpretation came in the form of Lord Kelvin's(William Thomson's) calculations of the heat flow from the Earth, and the implication this had for the age-- rather than hundreds of millions of years, the Earth could be as young as tens of million of years old.
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This evaluation was subsequently invalidated by the discovery of radioactivity in the last years of the 19thcentury, which was an unaccounted for source of heat in Kelvin's original calculations. With it factored in,the Earth could be vastly older. Estimates of the age of the Earth again returned to the prior methods.

The discovery of radioactivity also had another side effect, although it was several more decades before itsadditional significance to geology became apparent and the techniques became refined. Because of thechemistry of rocks, it was possible to calculate how much radioactive decay had occurred since an

appropriate mineral had formed, and how much time had therefore expired, by looking at the ratio betweenthe original radioactive isotope and its product, if the decay rate was known. Many geologicalcomplications and measurement difficulties existed, but initial attempts at the method clearly demonstratedthat the Earth was very old. In fact, the numbers that became available were significantly older than evensome geologists were expecting -- rather than hundreds of millions of years, which was the minimum ageexpected, the Earth's history was clearly at least billions of years long.

Radiometric dating provides numerical values for the age of an appropriate rock, usually expressed inmillions of years. Therefore, by dating a series of rocks in a vertical succession of strata previouslyrecognized with basic geologic principles (seeStratigraphic principles and relative time), it can provide anumerical calibration for what would otherwise be only an ordering of events -- i.e. relative dating obtainedfrom biostratigraphy (fossils), superpositional relationships, or other techniques. The integration of relativedating and radiometric dating has resulted in a series of increasingly precise "absolute" (i.e. numeric)geologic time scales, starting from about the 1910s to 1930s (simple radioisotope estimates) and becomingmore precise as the modern radiometric dating methods were employed (starting in about the 1950s).1

A Theoretical Example

To show how relative dating and numeric/absolute dating methods are integrated, it is useful to examine atheoretical example first. Given the background above, the information used for a geologic time scale canbe related like this:

Figure 2. How relative dating of events and radiometric (numeric) dates are combined to produce a calibratedgeological time scale. In this example, the data demonstrates that "fossil B time" was somewhere between 151 and

140 million years ago, and that "fossil A time" is older than 151 million years ago. Note that because of the positioof the dated beds, there is room for improvement in the time constraints on these fossil-bearing intervals (e.g., you

could look for a datable volcanic ash at 40-45m to better constrain the time of first appearance of fossil B).


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A continuous vertical stratigraphic section will provide the order of occurrence of events (column 1 ofFigure 2). These are summarized in terms of a "relative time scale" (column 2 ofFigure 2). Geologists canrefer to intervals of time as being "pre-first appearance of species A" or "during the existence of species A",or "after volcanic eruption #1" (at least six subdivisions are possible in the example inFigure 2). For thistype of "relative dating" to work it must be known that the succession of events is unique (or at least thatduplicate events are recognized -- e.g., the "first ash bed" and "second ash bed") and roughly synchronousover the area of interest. Unique events can be biological (e.g., the first appearance of a particular species

of organisms) or non-biological (e.g., the deposition of a volcanic ash with a unique chemistry andmineralogy over a wide area), and they will have varying degrees of lateral extent. Ideally, geologists arelooking for events that are unmistakably unique, in a consistent order, and of global extent in order toconstruct a geological time scale withglobalsignificance. Some of these events do exist. For example, theboundary between the Cretaceous and Tertiary periods is recognized on the basis of the extinction of alarge number of organisms globally (including ammonites, dinosaurs, and others), the first appearance ofnew types of organisms, the presence of geochemical anomalies (notably iridium), and unusual types ofminerals related to meteorite impact processes (impact spherules and shocked quartz). These types ofdistinctive events provide confirmation that the Earth's stratigraphy is genuinely successional on a globalscale. Even without that knowledge, it is still possible to construct local geologic time scales.

Although the idea that unique physical and biotic events are synchronous might sound like an"assumption", it is not. It can, and has been, tested in innumerable ways since the 19th century, in somecases by physically tracing distinct units laterally for hundreds or thousands of kilometres and looking very

carefully to see if the order of events changes. Geologists do sometimes find events that are "diachronous"(i.e. not the same age everywhere), but despite this deserved caution, after extensive testing, it is obviousthat many events really are synchronous to the limits of resolution offered by the geological record.

Because any newly-studied locality will have independent fossil, superpositional, or radiometric data thathave not yet been incorporated into the global geological time scale, all data types serve as both anindependent test of each other (on a local scale), and of the global geological time scale itself. The test ismore than just a "right" or "wrong" assessment, because there is a certain level of uncertainty in all agedeterminations. For example, an inconsistency may indicate that a particular geological boundary occurred76 million years ago, rather than 75 million years ago, which might be cause for revising the age estimate,but does not make the original estimate flagrantly "wrong". It depends upon the exact situation, and howmuch data are present to test hypotheses (e.g., could the range of a fossil be a bit different from what wasthought previously, or could the boundary between two time periods be a slightly different numerical age?).Whatever the situation, the current global geological time scale makespredictions about relationships

between relative and absolute age-dating at a local scale, and the input of new data means the globalgeologic time scale is continually refined and is known with increasing precision. This trend can be seen bylooking at the history of proposed geologic time scales

DEPOSITIONAL ENVIRONMENTS

Landscapesformand constantly change due to weathering and sedimentation. The area where sedimentaccumulates and is later buried by other sediment is known as its depositional environment. There are many large-scale, or regional, environments of deposition, as well as hundreds of smaller subenvironments within these regions.For example, rivers are regional depositional environments. Some span distances of hundreds of miles and contain alarge number of sub-environments, such as channels, backswamps, floodplains, abandoned channels, and sand bars.These depositional sub-environments can also be thought of as depositionallandforms, that is, land-forms producedby deposition rather than erosion.

Depositional environments are often separated into three general types, or settings: terrestrial (on land), marginal

marine (coastal), and marine (openocean). Examples of each of these three regional depositional settings are asfollows: terrestrial-alluvial fans, glacial valleys, lakes; marginal marine-beaches, deltas, estuaries, tidal mud andsand flats; marine-coral reefs, abyssal plains, andcontinental slope.

During deposition of sediments, physical structures form that are indicative of the conditions that created them.These are known as sedimentary structures. They may provide information aboutwater depth, current speed,environmental setting (for example, marine versus fresh water) or a variety of other factors. Among the morecommon of these are: bedding planes, beds, channels, cross-beds, ripples, and mud cracks.
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Bedding planes are the surfaces separating layers of sediment, or beds, in an outcrop of sediment orrock. The bedsrepresent episodes of sedimentation, while the bedding planes usually represent interruptions in sedimentation,either erosion or simply a lack of deposition.Beds and bedding planes are the most common sedimentary structures.

Rivers flow in elongated depressions called channels. When river deposits are preserved in the sediment record (forexample as part of a delta system), channels also are preserved. These channels appear in rock outcrops as narrow tobroad, v- or u-shaped, "bellies" or depressions at the base of otherwise flat beds. Preserved channels are sometimes

called cut-outs, because they "cut-out" part of the underlying bed.Submerged bars along a coast or in a river form when water currents or waves transport large volumes of sand orgravel along the bottom. Similarly, wind currents form dunes from sand on a beach or a desert. While thesedepositional surface features, orbedforms, build up in size, they also migrate in the direction of water or wind flow.This is known as bar or dune migration. Suspended load or bedload material moves up the shallowly inclined,upwind or upcurrent (stoss) side and falls over the crest of the bedform to the steep, downwind or downcurrent (lee)side. If the bedform is cut perpendicular to its long axis (from the stoss to the lee side) one would observe inclinedbeds of sediment, called cross-beds, which are the preserved leeward faces of the bedform. In an outcrop, thesecross-beds can often be seen stacked one atop another; some may be oriented in opposing directions, indicating achange in current or wind direction.

When a current or wave passes over sand or silt in shallow water, it forms ripples on the bottom. Ripples are actuallyjust smaller scale versions of dunes or bars. Rows of ripples form perpendicular to the flow direction of the water.When formed by a current, these ripples are asymmetrical in cross-section and move downstream by erosion of

sediment from the stoss side of the ripple, and deposition on the lee side. Wave-formed ripples on the ocean floorhave a more symmetrical profile, because waves move sediments back and forth, not just in one direction. In anoutcrop, ripples appear as very small cross-beds, known as cross-laminations, or simply as undulating beddingplanes.

When water is trapped in a muddy pool that slowly dries up, the slow sedimentation of theclay particles forms amud layer on the bottom of the pool. As the last of the water evaporates, the moist clay begins to dry up and crack,producing mud cracks as well as variably shaped mud chips known as mud crack polygons. Interpreting thecharacter of any of the sedimentary structures discussed above (for example, ripples) would primarily provideinformation concerning the nature of the medium of transport. Mud cracks, preserved on the surface of a bed, givesome idea of the nature of the depositional environment, specifically that it experienced alternating periods of wetand dry.

All clastic and organic sediments suffer one of two fates. Either they accumulate in a depositional environment, thenget buried and lithified (turned to rock by compaction and cementation) to produce sedimentary rock, or they are

reexposed by erosion after burial, but before lithification, and go through one or more new cycles of weathering-erosion-transport-deposition-burial.

PLATE TECTONICS

Some Past and Present Consequences

Plate tectonics has been responsible for many of the features that we find on the surface of the Earth today. A fewexamples include

The Appalachian Mountains were formed from wrinkling of the Earth's surface produced by the collisionof the North American and African plates.

The seismic and volcanic activity of the West Coast of the United States (for example, theSan AndreasFault) is produced by the grinding of the Pacific and North American Plates against each other. Indeed, theentire "ring of fire" around the Pacific, corresponding to regions of high volcanic and seismic activity, iscaused primarly by the motion of the Pacific Plate.

The Dead Sea in Israel is part of a rift system produced by plates that are pulling apart in that region.

The Himalayan Mountains were formed (indeed are still growing) as a result of the Indian subplateburrowing under the Eurasian plate and raising its edge.

Some Future Consequences of Plate Tectonics
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Plate tectonics is still an active process, and will drastically reshape the face of the Earth over the next 50 millionyears or so. A few consequences of plate tectonics based on projections of present motion include:

Portions of California will separate from the rest of North America.

The Italian "boot" will disappear.

Australia will become linked to Asia.

Africa will separate from the Near East.As a consequence of plate tectonics (supplemented by wind and water erosion), we live on the surface of a

geologically active planet that has obliterated most of its early geological history.

ROCK FORMATION/ROCK CYCLE

IGNEOUS ROCKS

Igneous means made from fire or heat. When volcanoes erupt and the liquid rock comes up to theearth's surface, then new igneous rock is made. When the rock is liquid & inside the earth, it is calledmagma. When the magma gets hard inside the crust, it turns intogranite. Most mountains are made ofgranite. It cools very slowly and is very hard.

When the magma gets up to the surface and flows out, like what happens when a volcano erupts,then the liquid is called lava. Lava flows down the sides of the volcano. When it cools & turns hard itis called obsidian, lava rock orpumice - depending on what it looks like.

Igneous rocks form when molten lava (magma) cools and turn to solid rock.The magma comes from the Earths core which is molten rock .The core makes up about 30% of the Total Earth Mass (31.5%)

Obsidian is natures glass. It forms when lava cools quickly on the surface. It is glassy andsmooth.

Pumice is full of air pockets that were trapped when the lava cooled when it frothed out ontothe surface.It is the only rock that floats.
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There are 5 kinds of igneous rocks, depending on the mix of minerals in the rocks.

Granite contains quartz, feldspar & mica

Diorite contains feldspar & one or more dark mineral. Feldspar is dominant.

Gabbro contains feldspar & one or more dark mineral. The dark minerals are dominant.

Periodotite contains iron and is black or dark.

Pegmatite is a coarse-grained granite with large crystals of quartz, feldspar and mica.

SEDIMENTARY ROCKS

When mountains are first formed, they are tall and jagged like the Rocky Mountains on the west coastof North America. Over time (millions of years) mountains become old mountains like the AppalachianMountains on the east coast of Canada and the United States. When mountains are old, they arerounded and much lower. What happens in the meantime is that lots of rock gets worn away due toerosion. Rain, freeze/thaw cycle, wind and running water cause the big mountains to crumble a little bitat a time.

Eventually most of the broken bits of the rock end up in the streams & rivers that flow down from themountains. These little bits of rock & sand are called sediments. When the water slows down enough,these sediments settle to the bottom of the lake or oceans they run into. Over many years, layers ofdifferent rock bits settle at the bottom of lakes and oceans.

Think of each layer as a page in a book. One piece of paper is not heavy. But a stack of telephonebooks is very heavy & would squish anything that was underneath. Over time the layers of sand andmud at the bottom of lakes & oceans turned into rocks. These are calledsedimentary rocks.

Some examples of sedimentary rocks are sandstone and shale.

Sedimentary rocks often have fossils in them.Plants & animals that have died get covered up by newlayers of sediment and are turned into stone. Most of the fossils we find are of plants & animals thatlived in the sea. They just settled to the bottom. Other plants & animals died in swamps, marshes or atthe edge of lakes.They were covered with sediments when the size of the lake got bigger.

When large amounts of plants are deposited in sedimentary rocks, then they turn into carbon. This gives

us our coal, oil, natural gas and petroleum. A large sea once covered the central part of Canada and theclimate was very tropical. In time, sedimentary rocks formed there. That is why we find dinosaur fossilsin Alberta and the area is a good source of natural fuels.

Sedimentary rocks cover 75% of the earths surface.Most of the rocks found on the Earths surface is sedimentary even though sedimentary rocksonly make up less than 5% of all the rocks that make up Earth.

When rocks are exposed to the elements air, rain, sun, freeze/thaw cycle, plants erosion occurs and the little bits of rock worn away get deposited as sediments.Over time, these sediments harden as they get buried by more sediments and turn intosedimentary rocks.

Sedimentary rocks are usually formed in layers called strata.

There are 6 main kinds of sedimentary rocks depending on the appearance of the rock.

Conglomerate rock has rounded rocks (pebbles, boulders) cemented together in a matrix. Sandstone is a soft stone that is made when sand grains cement together. Sometimes the

sandstone isdeposited in layers of different colored sand.

Shale is clay that has been hardened and turned into rock. It often breaks apart in large flatsections.

Limestone is a rock that contains many fossils and is made of calcium carbonate &/ormicroscopic shells.
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Gypsum, common salt or Epsom salt is found where sea water precipitates the salt as the waterevaporates.

Breccia has jagged bits of rock cemented together in a matrix.

Understanding Erosion & Sedimentary Rocks by Looking at Lint!

You may have a difficult time imagining something solid like rocks wearing down over time - buteverything does. If you take a look in the lint trap of your dryer, you will see that your clothes are beingworn away as they tumble in the dryer. In fact if there is enough lint - you will see how these bits havebeen laid down into layers - just like sediments at the bottom of the lake. You will see layers ofdifferent colors because the clothes you dried were different - just like you will see different layers ofrocks in sedimentary rocks. What is even more interesting is that if you scrunch up the lint a bit like inthe picture here, you can see the layers of lint bending - just like the layers of rock are bent. Lookcarefully at the rocks in road cuts and you sill see layers of rocks that have been folded just like the lintin your dryer. Neat eh?!

METAMORPHIC ROCKS

Metamorphic rocks are rocks that have changed.The word comes from the Greek "meta" and "morph" which means to change form. Metamorphic rocks were

originally igneous or sedimentary, but due to movement of the earth's crust, were changed.If you squeeze your hands together very hard, you will feel heat and pressure. When the earth's crust moves,it causes rocks to get squeezed so hard that the heat causes the rock to change. Marble is an example of asedimentary rock that has been changed into a metamorphic rock.

Metamorphic rocks are the least common of the 3 kinds of rocks.Metamorphic rocks are igneous or sedimentary rocks that have been transformed by great heat orpressure.

Foliated metamorphic rocks have layers, or banding.

Slate is transformed shale. It splits into smooth slabs.

Schist is the most common metamorphic rock. Mica is the most common mineral.

Gneiss has a streaky look because of alternating layers of minerals.

Non-foliated metamorphic rocks are not layered.

Marble is transformed limestone.

Quartzite is very hard.

EROSION

Erosion is a key part of the Rock Cycle. It is responsible for forming much of the interesting landscapethat is around us. It is also a major problem as people live in areas in large numbers and get used to theenvironment being in a certain way. People can do things to increase erosion or slow it down.

Erosion happens mainly as a result of weathering the effect of water, temperature and wind on thelandscape.

Water causes much erosion. When it falls as acid rain, it can dissolve rocks that are sensitive to acid.Marble & limestone weather when exposed to the rain. When the rain falls very heavily, as inmonsoons, then flooding can happen. Rivers with a lot or rushing water can cause mud slides and eroderiver banks. The action of waves on a beach causes much erosion. The waves pound on the rocks &over time, cliffs crumble. That is why you will often find sand & little pebbles on beaches. Rushingwater, like what you find in rivers that move quickly in the mountains or strong waves on the shores ofoceans, roll rocks around. This causes the sharp edges of the rocks to get knocked off & that is whyriver rocks are so smooth & beach pebbles look polished.

Acid Rain: chemicals in the air combine with precipitation
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When it rains it dissolves certain minerals sensitive to acid.

Leaching by ground water: water soaks into the soil, picks up chemicalsThis allows the water to leach or dissolve rocks it comes in contact with at bedrock.

Wave action at the beach: the waves tumble rocksRocks get ground down by the sand particles already on the beach, rocks smash against each

other & break. Fast moving water: rocks get picked up & carried when water runs swiftly

By bouncing along a river & smashing into other rocks, the sharp edges get knocked off.

Glaciers: large sheets of ice pick up large rocks, scrape bedrockRocks tumble in under-glacier rivers when glaciers melt.

Precipitation / Floods: heavy rain can cause floods which move & break rocks

Broken glass is tumbled on the beach and worn smooth by the action

of the waves.

Broken bits of shale tumble tothe bottom of hills and riverbanks. Then the are washed awayand tumbled by waves and water.

When they are deposited at theside of rivers and on the beach,they are smooth. This is causedby erosion.

The freeze / thaw cycle causes mountains to crumble over time and large rocks to breakdown into little rocks. When water gets into cracks in the rocks, this water expands during the freezecycle, making the cracks bigger. Then when the cracks fill up with water in the thaw period.This allowsmore water to go deeper into the rock which will make the rocks split apart when they freeze again. Thepower of frozen water expanding can be seen when you leave a glass bottle filled with liquid in thefreezer.

Wind, when it carries bits of sand and grit, can blast away layers of rocks.The wind can easily pick up little bits of sand and then sandblast the rocks that are in thewind's way.Sometimes only the soft layers of the rock are eroded, leaving interesting shapes.This kind of erosion usually only happens in very dry, desert like areas.

Other causes for rocks to break down & erode:

How hard / tough mineral is: softer, more friable rocks and minerals break up easily

Plant roots growing: plants get nutrients from the soil, seek out certain minerals likepotash,apatite for fertilizer, small roots go in cracks & break up mineral or rock when theroot grows bigger

Rock Falls: rocks tumbling down from a cliff or steep mountainside cause rocks tobreak up

Contact with soil: certain soils have chemicals in them that react with the chemicalmake up of rocks

STRUCTURAL GEOLOGY

Introduction

Structural geology is the study of the features formed by geological processes. Features include faults, folds anddipping strata. Geologists canworkout the order of events and see which events are related by taking fairly simplemeasurements and using simple methods.
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Measurements and Techniques

The most obvious thing to do when trying to decipher the structural history of a formation is to describe it. One wayof doing this is to measure the dip andstrike. The dip is the amount a bed of rock is tipped from the horizontal. Thestrike is the direction which is ninetydegrees from the dip, i.e. along the horizontal line on the bed. The strike can bein two directions, hence the dip could be in one of two directions also. There is a convention for the strike to be thein the direction you are facing if the rocks are dipping to your right. Some geologists prefer to measure the dip

direction, rather than strike, as it is slightly simpler. However, all maps use dip and strike, not dip direction.This is complicated slightly by apparent dip. This is due to the fact that you are not always looking edge on(perpendicular) to the bed you aremeasuring. If you are looking at a bed at a slight angle, then you see the apparentdip. The true dip will be greater than the apparent dip, as it is the maximum amount of dip, so the apparent dip canappear to be anything from 0 to the maximum (true) dip.

Figure 1: Dip and strike of abeddingplane.

In this diagram, the dip is 30, with a strike north/south (0/180), the dip direction is 270. On a geologicalmap, symbols are used for the dip and strike. The strike is represented by a bar, and the dip by a mark on the strikebar on the downdip direction with the dip written alongside, as shown on the map below left.

A geological cross section can be drawn from the map showing the subsurface structure. Obviously, only featureswhich can be seen on the surface can be represented. The cross-section below right is drawn using the values in themap alongside.

Figure 2a: A geological map Figure 2b: A cross section of the map

A technique which is used often is to plot values of dip and dip direction on a stereogram. A stereogram (orstereonet or hemispherical projection) is a way of representing 3-dimensional directions on a 2-dimensional surface.The net is a projection from the point onto the equator. A net is shown below.

The mechanisms of plotting points is shown in the next 4 diagrams.
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1 2

The points are placed all around the sphererepresenting 3D space.

The points are projected down onto the equatorial plane on aline which meets up at the south pole

3 4

The points are then "moved" onto the plane,which is your stereonet

The final stereonet.

To plot a bed onto the stereonet, use the following guide.1. Put tracing paper on stereonet

2. Draw around the circumference (known as the primitive circle or equator), and mark on North (and maybeSouth)

3. To plot a point with a 30 dip in a direction of 130, (written 30/130) plot a point on the equator 130around

4. Then rotate the tracing paper so that the point you've just plotted lies at 90

5. Then counting 30 in from the edge mark a second point. This is the point 30/130

A similar method is used to plot a pole to bedding, that is, a line which is perpendicular to the bedding surface.

1. Put tracing paper on stereonet

2. Draw around the circumference (known as the primitive circle or equator), and mark on North (and maybeSouth)

3. To plot a pole to a bed which is dipping at 30, in a direction of 130, (written 30/130) plot a point onthe equator 130 around

4. Then rotate the tracing paper so that the point you've just plotted lies at 90

5. Then counting 30 out from the centre to the opposite side to your first point, mark a second point. This isthe line perpendicular to the plane dipping 30/130

On a stereonet a line is represented by a point and a plane by a line.


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Folds

Folding of rocks is caused by the compression of rocks. This occurs slowly, over a long period of time. If thishappened quickly, the rocks would break, andfault. This is due to the mechanical properties of rocks, namely it'splastic nature. If a rock is stretched slowly, then it will behave in a ductile fashion. If stretched quickly, the rockbehaves in a brittle fashion. This behavior can be mimicked by using Blu-Tac. A typical fold is shown below,outlining the terms used in describing folds.

Figure 3: Nomenclature used when describing folds

Hinge: Where curvature of the fold is at a maximumCrest & Trough:

Where fold surface reaches a minimum and maximum respectivelyLimb:

Beds between two hingesAntiform & Synform:

Convex upwards or convex downward folds respectivelyAnticline & Syncline:

Older or younger beds at the core respectively. Can be used in conjunction with antiform and synform, i.e.an antiformal syncline

Folds are classified by shape and the chronological order of rocks in them. The shape of a fold is described by theangle between the limbs, which are given the terms:gentle (120-180), open (70-120), close (30-70), tight (5-

30) or isoclinal(0-5).The chronological order of the rocks in a fold are described by syncline and anticline, as described above.

Faults

Faults are caused by short-term stress on rocks. They occur discontinuously alongfault planes, and are the cause ofmost earthquakes. Faults are classified in terms of the type of force causing the fault which determines the directionof movement. There are many terms used in describing faults. These are shown in the diagram below.


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Figure 5: Fault nomenclature.

The strike is the horizontal distance moved. The throw is the vertical distance and the heave is the distance movedperpendicular to the fault.

The types of fault, with arrows showing motion, are shown below:

Diagram Name Mode of Formation...

Normal Fault Extension (tension)

Reverse Fault (or Thrust) Compression

Strike Slip Shear

Faults rarely fall exactly into these categories, as they have some of the other types of motion as well, particularlysome Strike Slip and rotational motion. Faults can also be reactivated, meaning a normal fault can be "reused" at alater time in a compressional regime. This produces complex drag folds along the side of a fault. Drag folds occur asthe rock is bent due to the movement of the fault.

Dome structures are found where forces deep under the crust have thrust a portion of the earth upward. The cuestasor overlapping folds face inward. Basins are similar, except the overlaps face outward as the structureforms adepression.

The average slackpacker will hike across numerous domes and basins in her life, but will rarely be aware of it. Thelower peninsula of Michigan, for example, is a giant basin formation. The city of Paris rests on a basin. More likely,the hiker will be aware of this phenomenon when encountering a smaller, local dome formation, such as UpheavalDome in Canyonlands National Park.

Basins

The Michigan basin, as an example, clearly exhibits the large scale basincaused by gently depressed layers of different geologic materials. Mostbasins are on a large scale such as this; "localized" basins are rare.

Photo at right shows the Michigan basin. This type of formation does notappear on your average local USGS topo map, and will not be evident to thehiker. Understanding the overall formation will assist in understandingsome of the smaller, local formations. As an example, the low sand hillsyou'll encounter hiking in parts of Michigan are evidence of glacially worncuestas, and in some places the "outward" facing cuestas are still visible.

Most of the features in the western USA referred to as "basins" are morecorrectly called esplanades, but they will always be called basins anyway.They are not basins as described in this entry; they are actually broad,somewhat flat areas found below mesas. Narrower esplanades are known as"benches." The formation of these features is completely different from thebasins caused by collapsinggeologydeep in the earth.
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Domes

Many domes are too large to be understood in terms of a normal map. Southern Ohio/Northern Kentucky rests on alarge scale dome. These are gently upward thrusts, created by movement deep within the earth (called subcrustalmovement). Some domes are circular, some are quite irregularly shaped.

Not all domes are enormous. Some are small, localized structures. These can be caused by a variety of phenomena.They can be caused by upward thrust or "arching" over large batholithic or laccolithic intrusions, they can be caused

by anticlines, or other deformations such as the salt dome illustrated below.A well known example of a local dome structure is Upheaval Dome in the "Island in the Sky" section ofCanyonlands National Park.

Localized Basins

This illustration, made during John Wesley Powell'sexploration of the Colorado RiverPlateau, is a "localbasin structure" somewhere in southwest Wyoming. Itshows the classic basin structure of a inward slopingdepression, ringed with outward facing cuestas. Obviouslocal basins such as this are rare; their exact cause isseldom known. We can intelligently conjecture that somedegradation and subsequent collapse is the cause.

Salt

Domes

The cross-section of a

typical salt dome, left, shows how the plug of salt creates a dome atthe surface. This is an approximation of what the salt domebelow Weeks Island, Louisiana -- see map below -- looks like. Weeks Island is actually a salt dome that protrudes up slightly above the surrounding marsh plain. Note the mine shaft plunging into thesalt plug, and the oilrigs taking advantage of the oil fields forcedupward by the upthrusting plug.

Salt domes are believed to be formed when large plugs of salt, some five miles deep in the earth, are forced up,pushing up layers as they go up. As the illustration shows, salt domes are often the site of salt mines and oil wells.

Upheaval Dome

Upheaval dome is an unusual feature amidst the canyons, mesas and esplanades ofCanyonlands National Park, near Moab, Utah. It is a cryptovolcanic type of dome,which means that it was created by an upward volcanic thrust. The inward facing
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cuestas are extremely steep and quite obvious. Notice in the photo above, the center ring of cuesta looks almost likea volcano; many confuse "volcanic dome" with "volcanic cone." The dome, like any others, is the actual surfacelayers of earth forced upward by the unseen plug beneath. In person, this is a jagged, haphazardous and disorientingfeature. Amidst the bizarre scenery of Canyonlands, it is striking, but certainly not the most striking feature in thepark. After viewing the sweeping vistas of Island in the Sky, many tourists wonder why they bothered to stop atUpheaval Dome. Indeed, without a passing interest in geology, their time would be better spent visiting otherlandmarks in the park

DETERMINING THICKNESS OF STRATA

I. Thickness of Strata

a) True Thickness- distance measured perpendicular to the upper and lower contact of a tabular

unit.

b) Apparent Thickness- vertical distance between an upper and lower contact in a non-horizontalunit. The apparent thickness is equal to the true thickness only when the attitude of the unit ishorizontal.

c) Outcrop Width- distance on the map between the bounding contacts of a tabular unitmeasured

along an azimuth perpendicular to strike.

d) Apparent Width- distance on the map between the upper and lower contacts of atabular

unit measured in a direction other than perpendicular to strike.

e) Special attitudes:

1. Vertical strata: if the map surface is relatively horizontal, the distance measuredperpendicular to the contacts is the true thickness.

2. Horizontal strata: the elevation difference between the upper and lowercontacts is the thickness.

f) Inclined strata on a horizontal map surface, traverse taken perpendicular to strike.

1. Map outcrop width is an apparent thickness termed the outcrop width (w).

2. Trig equations

sin(dip angle) = (opposite side)/(hypotenuse) = thickness/width (1)

g) Inclined strata below a horizontal topographic surface; traverse taken oblique to strike:

stratigraphic thickness = sin(dip angle) * (outcrop width)

1. First step must correct the apparent outcrop width (w') to the true outcrop width (w):

cos ($) = (w) / (w) (2)

(w) = cos($) * (w)

where beta is equal to an angle less than 90 between true dip direction bearing and traversedirection. In the below equations, (w) will represent true outcrop


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width, whereas (w) will represent apparent outcrop width.

2. Second step may be solved graphically by constructing a cross-section using the calculatedtrue map outcrop width (w) as is demonstrated below, or mathematically using equation(2).

h) Inclined strata on sloping map surface, traverse taken perpendicular to strike.

Figure 7-1: Cross-section of thickness problem.

1. Graphically construct the sloping map surface profile on the cross-section view.Then plot the dipping upper and lower contacts according to the outcrop width (w) obtainedfrom the traverse. Note that (w) is the distance actually traveled on the sloping surface- notthe distance between traverse endpoints measured from a map.

2. Trig formula will vary according to the relationship of the slope and dip directions.The best way is to inspect your graphical cross-section and decide whether the dip and slopeangles are added or subtracted to form the correct geometry.

3. As an example, given that the dip and slope are inclined in opposite directions:

Thickness = sin(dip angle + slope angle) * (w) (3)

Sin(dip angle + slope angle) = thickness / (w)

4. Note that in the special case where the slope surface is perpendicular to the stratigraphiccontacts, the sum of the dip angle and slope angle will equal 90, therefore the outcrop widthis equal to the true thickness.

i) Inclined strata on a sloping ground surface, traverse taken oblique to strike (this is the


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most general case).

The first step is to plot traverse on map, and then plot the strike of the upper and lower contactson the map. The slope distance component (w) is then calculated by measuring the lineperpendicular to the contacts.

w = (w) * cos($) (4)

The true thickness can then be solved graphically or trigonometrically as described above. Notethat one should measure the slope angle in the direction of (w), or estimate it from thetopographic map before proceeding to the next step.

After the outcrop width (w) is calculated, a cross section view is constructed using the measuredslope and dip angles along with the (w) value calculated in the above step.

JJ. Apparent thickness in a drillhole (Vertical apparent thickness or Depth)

a) It is often desirable to calculate the apparent stratigraphic thickness encountered in a drill hole. Inthese calculations it is often assumed that the drill hole is perfectly vertical. The graphical value is thenfound by measuring on the cross-section the vertical distance between the upper and lower contacts.

b) Trigonometric

cos(dip angle) = thickness / depth

(5)depth =thickness / (cos (dip angle))

Figure 7-2: Cross-section of depthproble

DETERMINE TRUE DIP


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Erosion sometimes exposes a portion of an ancient slipface such that its dip can be measureddirectly, but more often all that is available are cross-strata traces on an outcrop surface. In thatcase, each stratum, which is a line (or curve) appearing on the outcrop surface, plunges at anangle less than the true dip of the slipface plane containing it. To find the true dip, we need to useother information.

The slipface in diagram below (figure 3) slopes down toward us. Any plane (eg., an outcropsurface) cutting that slipface plane will create a stratum line, and any horizontal plane cutting theslipface plane will create a line of strike. The true dip of the slipface plane is the angle of dipmeasured in the plane perpendicular to its line of strike.

Usually an outcrop surface is not vertical or perpendicular to an ancient slipface within thesandstone. Most commonly we see intersections of slipface features (eg., pinstripes or grainflowlaminae) exposed as lines on an erosion surface (assuming the simple case where the entities are

all planar). We can measure the plunge and trend of any individual line on that surface, and ifwe're lucky (if it's exposed), we can measure the strike of the slipface plane. From thatinformation, we can calculate the true dip of the slipface plane, as derived below.


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GEOHAZARD

Japan has seen a number of tsunamis through out times, situated right there on theRing of Fire, and when theSumatran earthquake hit the ocean floor in the Indian ocean in 2004 creating the monster waves killing some 300000 people, tsunami became a household Japanese word, included in many languages.
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The Ring of Fire is an area where large numbers of earthquakes and volcanic eruptions occur in the basin of the

Pacific Ocean.

I visited Japan for the first time in 2001 and I did notice some signs showing a simplifiedwave when I was walkingthe streets of picturesque Kamakura, a coastal city a little south of Tokyo. I did not understand what they meant untillater, in 2004, when I was catapulted into the field of tsunamis and early warning systems. At the time I wasDirector of the European Sea Level Service, a network of tide gauges measuring sea level. Sea level change togetherwith seismic activity and crustal movements are the basic variables describing this geohazard.

What is a geohazard?

Geohazards can be defined as events related to the geological state and processes that may cause loss of lives as wellas material and environmental damages. These geohazards all arise from global geological processes inside theEarth, drivingdeformation and displacement of its crust. Underneath the thin crust the Earth consists of a sticky

fluid of melted rock we call the mantle that turns and twists like boiling water in slow motion, causing the crust tomove ever so slowly.
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Conceptual drawing of assumed convection cells in the mantle. Compared with boiling of water. Credit: USGS

The crust is divided in different plates (tectonic plates) and when these plates interact the resulting crustal movementcan cause earthquakes, allow volcanoes to erupt and set off landslides. All of these three; earthquakes, volcanoesand landslides can trigger tsunamis if they happen in or close to the ocean. These four geohazards are what I call theFantastic Fourin Planet Earth: Extreme Beauty Extreme Danger.

Earthquakes: Fractures in Earth's crust, or lithosphere (its crust and upper mantle), where sections of rock haveslipped past each other are called faults. Earthquakes are caused by the sudden release of accumulated strain alongthese faults, releasing energy in theform of low-frequency sound waves called seismic waves. A major earthquakeare usually followed by aftershocks. The epicenters of large earthquakes are normally located along knownseismically active zones, although the disruptive effects of an earthquake may extend over areas 100s of kilometersaway. Earthquakes may cause liquefaction, landslides, marine landslides and tsunamis.

Volcanoes: A volcano is defined by an opening in the Earth's crust from which lava, ash, and hot gases flow or areejected during an eruption. Volcanic hazards vary from one volcano to another and from one eruption to the next.The big killers are pyroclastic flows, lahars, and tsunamis triggered by volcanic eruptions. The most frequent lethalevents are so-calledtephra explosions very rapid jets of lava . The longest-lasting damage is usually inflicted by

thick lava flows or major collapses of volcanic edifices, as atMt. St. Helens in 1980.

Landslides: A landslide is a geohazard that involves the breakup and downhill flow of rock, mud, water andanything caught in the path. Landslides are one of the main processes by which landscapes evolve and the relatedhazards resultin a complex, changing landscape. Landslides both vary enormously in their distribution in space andtime, the amounts of energy produced during the activity and especially in size. This means that the resulting surfacedeformation or displacement varies considerably from one type of instability (that trigger the breakup) to another.Individual ground instabilities may have a common trigger, such as an extreme rainfall event or an earthquake, andtherefore occur alongside many equivalent occurrences over a large area. This means that they can have a significantregional impact.

Tsunamis: Tsunamis are gravity waves (different physical features than wind induced surface waves) created by arapid displacement of a water column. The displacement can be the result of earthquakes, volcanic eruptions orlandslides. These energetic waves travel fast with long wavelengths and relatively small amplitudes in open ocean.When hitting shallow water they build up an amplitude and can become tens, and on very rare occasions, evenhundreds of meters high. The coastal inundation can be devastating and catastrophic.

Extreme geohazards

The Sumatran earthquake/Indian ocean tsunami was one of the most extreme geohazard in modern history (see listof earthquakes). This extreme reached us all, beyond the mere geophysical waves. As tourists come from all over theworld to visit the beautiful shores of the Indian ocean, the 2004 tsunami affected people from around the globe. Theextent of it's destruction and the dimension of the disaster are parts of the definition of extreme. That, combined withtheir physical features that normally are several orders higher or more powerful than the average geohazard. So,

when we talk about extreme geohazards we not only refer to the physical characteristics of the geohazard but alsothe risk they represent in terms of consequences of this hazard.

Chilean 1960 earthquake/tsunami is considered the largest or most extreme geohazard and natural disaster inmodern history. Since there were several warning foreshocks the earthquake itself did not take that many lives, butthe tsunami came as a surprise and in turn led to the construction of the Pacific tsunami early warning system.

The 7.8 magnitude earthquake in Tangshan, China, in 1976, is the most deadly earthquake ever recorded. The
http://www.science20.com/http://www.science20.com/planetbye/planet_earth_extreme_beauty_%E2%80%93_extreme_danger-84783http://www.science20.com/http://www.science20.com/http://hvo.wr.usgs.gov/hazards/oceanentry/deltaexplosions/http://hvo.wr.usgs.gov/hazards/oceanentry/deltaexplosions/http://www.science20.com/planetbye/mount_st_helens_devastating_reawakening_30_years_agohttp://www.science20.com/planetbye/mount_st_helens_devastating_reawakening_30_years_agohttp://www.science20.com/http://www.science20.com/http://earthquake.usgs.gov/earthquakes/world/10_largest_world.phphttp://earthquake.usgs.gov/earthquakes/world/10_largest_world.phphttp://en.wikipedia.org/wiki/1976_Tangshan_earthquakehttp://en.wikipedia.org/wiki/1976_Tangshan_earthquakehttp://www.science20.com/http://www.science20.com/planetbye/planet_earth_extreme_beauty_%E2%80%93_extreme_danger-84783http://www.science20.com/http://hvo.wr.usgs.gov/hazards/oceanentry/deltaexplosions/http://www.science20.com/planetbye/mount_st_helens_devastating_reawakening_30_years_agohttp://www.science20.com/http://earthquake.usgs.gov/earthquakes/world/10_largest_world.phphttp://earthquake.usgs.gov/earthquakes/world/10_largest_world.phphttp://en.wikipedia.org/wiki/1976_Tangshan_earthquake


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number of deaths is however unclear (I've seen between 250 000 - 800 000) to date as the Chinese for politicalreasons towards the end of the Cultural Revolution did not want to deal with the disaster other than saying that thedisaster stricken would and should rescue themselves etc.

Really extreme geohazards megastunamis and supervolcanoes

Norway is situated in a safe distance from the Ring of Fire. Crustal movements in this part of the world are very

slow stemming from post glacial rebound, the uplift of ground due to the absence of heavy glaciers that meltedthousands of years ago. Norway has in fact a rather high number of earthquakes as well but these far from qualify asextreme geohazards. But, if we look at the geological history of Norway we find evidence of a really extremegeohazard. More than 8000 years ago, the submarine Storegga landslide caused a wide ranging megatsunami hittingmost of our entire coastline.

The dimension of both the Storegga slide itself and the resulting tsunami is almost incomprehensible. We cannoteven begin to think what damage such a tsunami would do to Norwegian oil industry, fisheries and our coastalpopulation if it would have taken place today.

Moving over the North Atlantic and almost to the West coast of the US in Wyoming, we find the beautifulYellowstone national park. Yellowstone is known for its wildlife and its many geothermal features such as geysirs.This park is namely situated on the top of a vast calderas from several volcano eruptions so big thatYellowstonemerits the name supervolcano. Yellowstone is monitored by scientists that for obvious reasons find this placeparticularly interesting, and they report that there areno signs that indicate the supervolcano is about to erupt anytime soon
http://www.yellowstonenationalpark.com/http://www.yellowstonenationalpark.com/http://en.wikipedia.org/wiki/Yellowstone_Calderahttp://en.wikipedia.org/wiki/Yellowstone_Calderahttp://www.nasa.gov/topics/earth/features/2012-superVolcano.htmlhttp://www.nasa.gov/topics/earth/features/2012-superVolcano.htmlhttp://www.yellowstonenationalpark.com/http://en.wikipedia.org/wiki/Yellowstone_Calderahttp://www.nasa.gov/topics/earth/features/2012-superVolcano.html

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Additional Geologic Mapping Notes