Geological Geological ProcessesProcesses

OverviewOverview Meet the EarthMeet the Earth Development of plate Development of plate

tectonic theory: what is tectonic theory: what is right isn’t always right isn’t always popularpopular

Supporting evidence of Supporting evidence of the theory of continental the theory of continental drift and plate tectonicsdrift and plate tectonics

Three main types of Three main types of plate boundaries- fun plate boundaries- fun activityactivity

Volcanoes and Volcanoes and earthquakesearthquakes

Layers of the Layers of the EarthEarth

Continental crust is an Continental crust is an average of 30-40 km thick average of 30-40 km thick (can be up to 100 km thick on (can be up to 100 km thick on the craton)the craton)

Oceanic crust is ~6-7 km Oceanic crust is ~6-7 km thickthick

The uppermost mantle The uppermost mantle behaves rigidly (like a solid), behaves rigidly (like a solid), and together with the and together with the overlying crust is referred to overlying crust is referred to as the lithosphereas the lithosphere

Underneath the lithosphere Underneath the lithosphere is the less rigid is the less rigid asthenosphere, which is asthenosphere, which is partially moltenpartially molten

Below about 200 km the Below about 200 km the mantle is fully solidmantle is fully solid

The Core:The Core: core is larger than Mars!core is larger than Mars! made up of two distinct made up of two distinct

layers: a liquid outer layer layers: a liquid outer layer and a solid inner core.and a solid inner core.

made up of metallic iron-made up of metallic iron-nickel alloy nickel alloy

What is a plate?What is a plate?

a massive, irregularly shaped slab of solid rock, generally composed of both a massive, irregularly shaped slab of solid rock, generally composed of both continental and oceanic lithosphere. continental and oceanic lithosphere.

Most of the boundaries between individual plates cannot be seen, because Most of the boundaries between individual plates cannot be seen, because they are hidden beneath the oceans.they are hidden beneath the oceans.

Source: www.nature.nps.gov/.../usgsnps/pltec/pltec1.html

Quaking and shaking…Quaking and shaking…

Humans are curious…..Humans are curious….. Why is the Earth so restless? Why is the Earth so restless? What causes the ground to shake What causes the ground to shake

violently?violently? Why do volcanoes erupt?Why do volcanoes erupt? Why are our mountain ranges so Why are our mountain ranges so

tall?tall?

Early thoughts…Early thoughts… Until the 1700s, most Europeans thought that Until the 1700s, most Europeans thought that

a Biblical Flood played a major role in a Biblical Flood played a major role in shaping the Earth's surface. shaping the Earth's surface. ““CatastrophismCatastrophism”” : : the belief that all earthly the belief that all earthly

changes were sudden and caused by a series of changes were sudden and caused by a series of catastrophes. catastrophes.

Mid-19th century: Mid-19th century: catastrophism => catastrophism => "uniformitarianism""uniformitarianism" "Uniformitarian Principle" (James Hutton, 1785): "Uniformitarian Principle" (James Hutton, 1785):

THE PRESENT IS THE KEY TO THE THE PRESENT IS THE KEY TO THE PASTPAST

Geologic forces that act on the Earth today are the Geologic forces that act on the Earth today are the same as those that have acted in the geologic past. same as those that have acted in the geologic past.

Continental DriftContinental Drift Predecessor to Predecessor to

modern plate modern plate tectonicstectonics

Shape and “fit” Shape and “fit” of the continents of the continents was the initial was the initial evidenceevidence Snider-Pelligrini Snider-Pelligrini

(1858): ideas (1858): ideas were mostly were mostly ignoredignored

Wegner (1915)Wegner (1915)Source: http://pubs.usgs.gov/gip/dynamic/historical.html

1858: Snider-Pelligrini drawings

Continental DriftContinental Drift Alfred Wegener (1880-Alfred Wegener (1880-

1930)1930) Proposed all of the Proposed all of the

continents were once part of continents were once part of a large supercontinent - a large supercontinent - PangaeaPangaea

Based on:Based on: Similarities in shorelines Similarities in shorelines Distinctive rock and fossil Distinctive rock and fossil

groups found in Africa & groups found in Africa & South AmericaSouth America

Ideas were not widely Ideas were not widely acceptedaccepted

Froze to death in 1930 during Froze to death in 1930 during an expedition crossing the an expedition crossing the Greenland ice capGreenland ice cap

Source: http://pubs.usgs.gov/gip/dynamic/wegener.html

Evidence for Continental Evidence for Continental DriftDrift

Paleontological: Similarity of fossils on opposite sides of the Paleontological: Similarity of fossils on opposite sides of the Atlantic and Indian Oceans, ex. Atlantic and Indian Oceans, ex. Mesosaurus, GlossopterisMesosaurus, Glossopteris

Problem: Perhaps similar animals had evolved in these Problem: Perhaps similar animals had evolved in these areas (convergent evolution). Perhaps there were floating areas (convergent evolution). Perhaps there were floating pieces of crust that rafted animals and plant seeds across? pieces of crust that rafted animals and plant seeds across? Transoceanic land bridges?Transoceanic land bridges?

Source: http://pubs.usgs.gov/gip/dynamic/continents.html

Evidence for Evidence for Continental DriftContinental Drift

Rock types and structures: Distinct rock type and Rock types and structures: Distinct rock type and geologic structures on both sides of the Atlantic geologic structures on both sides of the Atlantic OceanOcean

Problem: Erosion and weathering breaks down Problem: Erosion and weathering breaks down rocks over time. How could the continents still rocks over time. How could the continents still “fit” together after millions of years of wear and “fit” together after millions of years of wear and tear?tear?

Source: http://pubs.usgs.gov/gip/dynamic/continents.html

Evidence for Evidence for Continental DriftContinental Drift

PaleoclimatePaleoclimate Evidence of extreme changes in climate as Evidence of extreme changes in climate as

compared to the present (glacial deposits in present compared to the present (glacial deposits in present day deserts)day deserts)

Problem: Perhaps there was a total global Problem: Perhaps there was a total global cooling event cooling event

Source: http://pubs.usgs.gov/gip/dynamic/continents.html

Development of Plate Development of Plate Tectonic TheoryTectonic Theory

Wegener’s theory was dismissed as being Wegener’s theory was dismissed as being eccentric, preposterous, and improbableeccentric, preposterous, and improbable..

Original evidence for continental drift Original evidence for continental drift was ONLY from continental rockswas ONLY from continental rocks

Technological advances in the 1950’s Technological advances in the 1950’s and 1960’s allowed investigation of the and 1960’s allowed investigation of the sea floor and oceanic rockssea floor and oceanic rocks

Geophysics & paleomagnetism Geophysics & paleomagnetism provided new dataprovided new data

Harry Hess- Sea floor Harry Hess- Sea floor spreadingspreading

From the 1940’s to the 60’s, Harry Hess made many key intellectual contributions to the coming revolution in geologic thought: “Father of Plate Tectonics” Helped provide more evidence to support Wegener’s

theories Echo-sounding of sea floor revealed deep sea

features and the topography of mid-ocean ridges ridges are areas of high heat flow and volcanic

activity young age of ocean floor, based on thickness of

sediment Hot material rose out of ridges (spreading

centers) and moved across the sea floor, crust was recycled.

Earth’s magnetic field Earth’s magnetic field provides more evidenceprovides more evidence

The Earth has an invisible magnetic field (all free-floating magnets at the Earth’s surface point to magnetic north)---Think about a compass.

Iron-rich minerals crystallizing from molten rock will orient towards magnetic north when they cool below the Curie point, the temperature above which permanent magnetism is impossible (580 degrees C for magnetite).

Thus lavas lock in the record of Earth’s magnetic field when they form.

MagnometersMagnometers Adapted from airborne

devices developed during World War II to detect submarines

Used to recognize odd magnetic variations across the ocean floor.

Discovered magnetic “stripes” on the sea floor Rocks formed over time

will record either a “normal” magnetic orientation or “reversed”

Magnetic reversals are global phenomena and can be used for global stratigraphic correlation

http://pubs.usgs.gov/gip/dynamic/developing.html

Evidence for plate Evidence for plate tectonicstectonics

Demonstration of the ruggedness and youth of Demonstration of the ruggedness and youth of the ocean floor the ocean floor

Confirmation of repeated reversals of the Confirmation of repeated reversals of the Earth magnetic field in the geologic pastEarth magnetic field in the geologic past

Emergence of the seafloor-spreading Emergence of the seafloor-spreading hypothesis and associated recycling of hypothesis and associated recycling of oceanic crustoceanic crust

Precise documentation that the world's Precise documentation that the world's earthquake and volcanic activity is earthquake and volcanic activity is concentrated along oceanic trenches and concentrated along oceanic trenches and submarine mountain rangessubmarine mountain ranges

So…why do the plates So…why do the plates move?move?

Plate tectonics is:Plate tectonics is: a geological a geological theorytheory that pieces of Earth’s that pieces of Earth’s

lithosphere are in lithosphere are in constant, slow motion, constant, slow motion, driven by convection driven by convection currents in the mantle. currents in the mantle.

explains the formation, explains the formation, movement, and movement, and subduction of Earth’s subduction of Earth’s plates. plates.

The plates of the lithosphere The plates of the lithosphere float on top of the float on top of the asthenosphere. Convection asthenosphere. Convection currents rise in the currents rise in the asthenosphere and spread asthenosphere and spread out beneath the lithosphere.out beneath the lithosphere.

HEAT

Types of Plate Types of Plate BoundariesBoundaries

http://cimss.ssec.wisc.edu/sage/geology/lesson2/images/concepts_fig8.gif

Plate boundariesPlate boundaries

Divergent: plates are pulling away Divergent: plates are pulling away from each otherfrom each other

Convergent: Plates are colliding and Convergent: Plates are colliding and one is subducted under the otherone is subducted under the other

Transform: Plates are sliding past Transform: Plates are sliding past each othereach other

Snickers Bar Snickers Bar ActivityActivity

Snickers Bar Activity- Snickers Bar Activity- Step 1Step 1

Obtain a Snickers bar. Unwrap the bar and make Obtain a Snickers bar. Unwrap the bar and make a few cracks across the top middle portion of its a few cracks across the top middle portion of its top. top.

What does the chocolate on each side of the cracks What does the chocolate on each side of the cracks represents.represents.

a tectonic platea tectonic plateThe Earth is covered with several tectonic The Earth is covered with several tectonic plates. We live on the North American Plateplates. We live on the North American Plate

What does the nougat/ caramel portion What does the nougat/ caramel portion represent?represent?

The asthenosphereThe asthenosphere

Snickers Bar Activity- Snickers Bar Activity- Step 2Step 2

Hold each end of the candy bar with Hold each end of the candy bar with your thumb and forefinger and SLOWLY your thumb and forefinger and SLOWLY stretch the candy bar, pulling it no more stretch the candy bar, pulling it no more than 1/2 to 1 inch apart.than 1/2 to 1 inch apart.

What kind of plate boundary have you What kind of plate boundary have you made?made?

A Divergent Plate boundaryA Divergent Plate boundary

Snickers Bar Activity- Snickers Bar Activity- Step 3Step 3

Push the candy bar back together. Push the candy bar back together. Continue adding pressure until one piece Continue adding pressure until one piece of chocolate moves beneath another. of chocolate moves beneath another.

What kind of plate boundary have you What kind of plate boundary have you made?made?

A Convergent Plate A Convergent Plate boundaryboundary

Snickers Bar Activity- Snickers Bar Activity- Step 4Step 4

Pull the bar back to its normal Pull the bar back to its normal shape. Push one side forward and shape. Push one side forward and pull one side back. pull one side back. What kind of What kind of plate boundary have you made?plate boundary have you made?

A Transform Plate A Transform Plate boundaryboundary

The Consequences The Consequences of Plate of Plate

Movement…Movement…volcanoes and volcanoes and earthquakesearthquakes

What is a volcano?What is a volcano? A place on the earth’s A place on the earth’s

surface (or any other surface (or any other planet) where molten planet) where molten rock and gases are rock and gases are erupted.erupted.

There are, however, There are, however, many kinds of volcanoes. many kinds of volcanoes.

Volcano does not have to Volcano does not have to be a beautiful be a beautiful snowcapped conical snowcapped conical peak (Mt St Helens). It peak (Mt St Helens). It can be a hole in the can be a hole in the ground, or a crack in the ground, or a crack in the earth’s surfaceearth’s surface

Most volcanoes occur at Most volcanoes occur at convergent boundariesconvergent boundaries

Types of VolcanoesTypes of Volcanoes

Why do volcanoes erupt?Why do volcanoes erupt? Hot, molten rock (magma) is buoyant (has a lower Hot, molten rock (magma) is buoyant (has a lower

density than the surrounding rocks) and will rise up density than the surrounding rocks) and will rise up through the crust to erupt on the surface.through the crust to erupt on the surface. Same principle as hot air rising, e.g. how a hot air balloon Same principle as hot air rising, e.g. how a hot air balloon

worksworks When magma reaches the surface it depends on how When magma reaches the surface it depends on how

easily it flows (viscosity) and the amount of gas easily it flows (viscosity) and the amount of gas (H(H22O, COO, CO22, S) it has in it as to how it erupts., S) it has in it as to how it erupts.

Large amounts of gas and a high viscosity (sticky) Large amounts of gas and a high viscosity (sticky) magma will form an explosive eruption!magma will form an explosive eruption! Think about shaking a carbonated drink and then releasing Think about shaking a carbonated drink and then releasing

the cap.the cap. Small amounts of gas and (or) low viscosity (runny) Small amounts of gas and (or) low viscosity (runny)

magma will form an effusive eruptionmagma will form an effusive eruption Where the magma just trickles out of the volcano (lava Where the magma just trickles out of the volcano (lava

flow).flow).

Volcanic HazardsVolcanic Hazards Pyroclastic flowPyroclastic flow Lahars/Mud flowsLahars/Mud flows Pyroclastic and ash Pyroclastic and ash

fallfall Lava flowLava flow Noxious GasNoxious Gas Earthquakes: Earthquakes: Large Large

volumes of magma volumes of magma moving through the moving through the shallow crust can shallow crust can cause large cause large earthquakes.earthquakes.

What is an earthquake?What is an earthquake?

a tremor of the a tremor of the earth's surface earth's surface usually triggered usually triggered by the release of by the release of underground underground stress along fault stress along fault lines. This release lines. This release causes movement causes movement in masses of rockin masses of rock

Epicenter and FocusEpicenter and Focus

EarthquaEarthquake waveske waves

Body WavesBody Waves Primary or Compressional: P- wavesPrimary or Compressional: P- waves Secondary or Shear: S- wavesSecondary or Shear: S- waves

Surface Waves (won’t discuss these)Surface Waves (won’t discuss these) Raleigh (large vertical displacements)Raleigh (large vertical displacements) Love (shear)Love (shear)

How do we measure How do we measure earthquakesearthquakes

Richter scaleRichter scale invented by Charles F. Richter in 1934. invented by Charles F. Richter in 1934. calculated from the amplitude of the largest seismic wave calculated from the amplitude of the largest seismic wave

recorded for the earthquake, no matter what type of wave recorded for the earthquake, no matter what type of wave was the strongest.was the strongest.

based on a logarithmic scale (base 10). What this means is based on a logarithmic scale (base 10). What this means is that for each whole number you go up on the Richter scale, that for each whole number you go up on the Richter scale, the amplitude of the ground motion recorded by a the amplitude of the ground motion recorded by a seismograph goes up ten times. seismograph goes up ten times.

Mercalli scaleMercalli scale. . invented by Giuseppe Mercalli in 1902invented by Giuseppe Mercalli in 1902 uses the observations of the people who experienced the uses the observations of the people who experienced the

earthquake to estimate its intensity. earthquake to estimate its intensity. isn't considered as scientific as the Richter scaleisn't considered as scientific as the Richter scale witnesses of the earthquake might exaggerate just how bad witnesses of the earthquake might exaggerate just how bad

things were during the earthquake and you may not find two things were during the earthquake and you may not find two witnesses who agree on what happened; everybody will say witnesses who agree on what happened; everybody will say something different. something different.

SeismographSeismograph

How we measure How we measure earthquake wavesearthquake waves

Determines depth Determines depth and magnitude of and magnitude of quakesquakes

Earthquake fact Earthquake fact or fictionor fiction

Mega- Quakes, as seen in Mega- Quakes, as seen in “10.5”“10.5”

The truth: THEORETICALLY, YES. The truth: THEORETICALLY, YES. REALISTICALLY, NO.REALISTICALLY, NO. The magnitude of an earthquake is related to the The magnitude of an earthquake is related to the

length of the fault on which it occurs length of the fault on which it occurs -- the longer the fault, the larger the earthquake. -- the longer the fault, the larger the earthquake.

No fault long enough to generate a magnitude 10.5 No fault long enough to generate a magnitude 10.5 earthquake is known to exist. earthquake is known to exist.

The largest earthquake ever recorded was a The largest earthquake ever recorded was a magnitude 9.5 on May 22, 1960 in Chile on a fault magnitude 9.5 on May 22, 1960 in Chile on a fault that is almost 1,000 miles long. that is almost 1,000 miles long.

We can’t rule out a Mega-Quake because diagnostic We can’t rule out a Mega-Quake because diagnostic equipment has only been around for about 100 years, equipment has only been around for about 100 years, insignificant when compared to geologic time.insignificant when compared to geologic time.

California has the most California has the most earthquakes in the USearthquakes in the US

The truth: The truth: Alaska registers the most Alaska registers the most earthquakes in a given year. earthquakes in a given year.

California= the most damaging California= the most damaging earthquakes because of its greater earthquakes because of its greater population and extensive infrastructure. population and extensive infrastructure.

Alaska’s large earthquakes occur in Alaska’s large earthquakes occur in remote locations such as along the remote locations such as along the Aleutian Island chain. Aleutian Island chain.

Florida and North Dakota have the fewest Florida and North Dakota have the fewest earthquakes each year. earthquakes each year.

The ground can open up The ground can open up during an earthquake.during an earthquake.

The truth: NO WAY!!!The truth: NO WAY!!! Gaping faults exist Gaping faults exist only in movies and novels. The ground only in movies and novels. The ground moves across a fault during an earthquake, moves across a fault during an earthquake, not away from it, due to friction. If the fault not away from it, due to friction. If the fault could open, there would be no friction. could open, there would be no friction. Without friction, there would be no Without friction, there would be no earthquake. Shallow crevasses can form earthquake. Shallow crevasses can form during earthquake induced landslides, during earthquake induced landslides, lateral spreads, or other types of ground lateral spreads, or other types of ground failures, but the fault line itself does not failures, but the fault line itself does not open.open.

California will eventually California will eventually fall into the oceanfall into the ocean..

Sorry Lex Luthor… NO WAY!! Sorry Lex Luthor… NO WAY!! It’s absolutely It’s absolutely impossible that California will be swept out to impossible that California will be swept out to sea. Instead, southwestern California is sea. Instead, southwestern California is moving horizontally northward towards Alaska moving horizontally northward towards Alaska as it slides past central and eastern California. as it slides past central and eastern California. California sits on the Pacific Plate which is California sits on the Pacific Plate which is moving to the northwest with respect to the moving to the northwest with respect to the North American Plate at approximately 46 North American Plate at approximately 46 millimeters (two inches) per year (the rate millimeters (two inches) per year (the rate your fingernails grow). your fingernails grow). In about 15 million years, Los Angeles and San In about 15 million years, Los Angeles and San

Francisco will be next-door neighborsFrancisco will be next-door neighbors In about 85 million years, Los Angeles residents In about 85 million years, Los Angeles residents

will find themselves with an Alaska zip code! will find themselves with an Alaska zip code!

People can cause People can cause earthquakes.earthquakes.

A glimmer of hope for Lex Luthor…A glimmer of hope for Lex Luthor…PARTIALLY FACT: PARTIALLY FACT: Earthquakes induced by Earthquakes induced by human activity have been documented in a human activity have been documented in a few locations in the United States, Japan, and few locations in the United States, Japan, and Canada. The cause was injection of fluids into Canada. The cause was injection of fluids into deep wells for waste disposal and secondary deep wells for waste disposal and secondary recovery of oil, and the filling of large recovery of oil, and the filling of large reservoirs for water supplies. Most of these reservoirs for water supplies. Most of these earthquakes were minor. Deep mining can earthquakes were minor. Deep mining can cause small to moderate quakes and nuclear cause small to moderate quakes and nuclear testing has caused small earthquakes in the testing has caused small earthquakes in the immediate area surrounding the test site, but immediate area surrounding the test site, but other human activities have not been shown other human activities have not been shown to trigger subsequent earthquakes. to trigger subsequent earthquakes.

We can predict earthquakes.We can predict earthquakes.

IF ONLY… IF ONLY… Earthquake prediction is the Earthquake prediction is the holy grail for earthquake scientists, but holy grail for earthquake scientists, but there currently is no accepted method to there currently is no accepted method to accomplish the goal of predicting the time, accomplish the goal of predicting the time, place and magnitude of an impending place and magnitude of an impending quake. Most research is focused on long quake. Most research is focused on long range (next 30 years) , not 1-5 years. We range (next 30 years) , not 1-5 years. We can predict the type of ground motion to can predict the type of ground motion to expect based on the geology and the expect based on the geology and the history of earthquake activity of the history of earthquake activity of the region, but not when the motion will occur.region, but not when the motion will occur.