Week3+4 Natural Environmental Hazards- part1

Dr. Mohammed Ajjour University Of Palestine

2009,

Earthquakes An earthquake is the vibration, sometimes violent, of the

Earth's surface that follows a release of energy in the Earth's crust. This energy can be generated by a sudden dislocation of segments of the crust, by a volcanic eruption, or event by manmade explosions. Most destructive quakes, however, are caused by dislocations of the crust. The crust may first bend and then, when the stress exceeds the strength of the rocks, break and "snap" to a new position. In the process of breaking, vibrations called "seismic waves" are generated. These waves travel outward from the source of the earthquake along the surface and through the Earth at varying speeds depending on the material through which they move. Some of the vibrations are of high frequency to be audible, while others are of very low frequency.

University Of Palestine 2009, Dr. Mohammed Ajjour

Earthquakes An aftershock is an earthquake of a smaller

magnitude that occurs after a previous earthquake, the mainshock.

earthquakes can occur almost anywhere, Larger earthquakes occur less frequently, the relationship being exponential; for example, roughly ten times as many earthquakes larger than magnitude 4 occur in a particular time period than earthquakes larger than magnitude 5. Most of the world's earthquakes (90%, and 81% of the largest) take place in the 40,000-km-long, horseshoe-shaped zone called the circum-Pacific seismic belt, known as the Pacific Ring of Fire, which for the most part bounds the Pacific Plate. Massive earthquakes tend to occur along other plate boundaries, too, such as along the Himalayan Mountains.

University Of Palestine 2009, Dr. Mohammed Ajjour

Earthquakes Frequency and magnitude of

Earthquakes depend on type of movement of plates:

Plates moving apart : rare occurrence, and if with little magnitude ,

Plates move against each other : very often, with high magnitude ,

Plates slip beside each other : very rare, and if with low magnitude

University Of Palestine 2009, Dr. Mohammed Ajjour

Earthquakes Geologists have found that earthquakes tend to reoccur along faults, which

reflect zones of weakness in the Earth's crust. Even if a fault zone has recently experienced an earthquake, however, there is no guarantee that all the stress has been relieved. Another earthquake could still occur.

A fault is a fracture in the Earth's crust along which two blocks of the crust have slipped with respect to each other. Faults are divided into three main groups, depending on how they move. Normal faults occur in response to pulling or tension; the overlying block moves down the dip of the fault plane. Thrust (reverse) faults occur in response to squeezing or compression; the overlying block moves up the dip of the fault plane. Strike-slip (lateral) faults occur in response to either type of stress; the blocks move horizontally past one another

The epicenter of an earthquake is the point on the Earth's surface directly above the focus. The location of an earthquake is commonly described by the geographic position of its epicenter and by its focal depth.

University Of Palestine 2009, Dr. Mohammed Ajjour

Earthquakes Shaking and ground rupture :Shaking and ground rupture

are the main effects created by earthquakes, principally resulting in more or less severe damage to buildings and other rigid structures. The severity of the local effects depends on the complex combination of the earthquake magnitude, the distance from the epicenter, and the local geological and geomorphologic conditions, which may amplify or reduce wave propagation .

Earthquakes may lead to disease, lack of basic necessities, loss of life, higher insurance premiums, general property damage, road and bridge damage, and collapse or destabilization of buildings. Earthquakes can also precede volcanic eruptions, which cause further problems; for example, substantial crop damage .

University Of Palestine 2009, Dr. Mohammed Ajjour

Earthquakes Soil liquefaction : Soil liquefaction occurs when, because

of the shaking, water-saturated granular material (such as sand) temporarily loses its strength and transforms from a solid to a liquid. Soil liquefaction may cause rigid structures, like buildings and bridges, to tilt or sink into the liquefied deposits. This can be a devastating effect of earthquakes. For example, in the 1964 Alaska earthquake , soil liquefaction caused many buildings to sink into the ground, eventually collapsing upon themselves.[

Tsunami :Tsunamis are long-wavelength, long-period sea waves produced by the sudden or abrupt movement of large volumes of water. In the open ocean the distance between wave crests can surpass 100 kilometers , and the wave periods can vary from five minutes to one hour. Such tsunamis travel 600-800 kilometers per hour), depending on water depth. Large e.[

University Of Palestine 2009, Dr. Mohammed Ajjour

Earthquakes waves produced by an earthquake or a submarine

landslide can overrun nearby coastal areas in a matter of minutes. Tsunamis can also travel thousands of kilometers across open ocean and wreak destruction on far shores. Ordinarily, subduction earthquakes under magnitude 7.5 on the Richter scale do not cause tsunamis, although some instances of this have been recorded. Most destructive tsunamis are caused by earthquakes of magnitude 7.5 or more

Landslides and avalanches :Earthquakes, along with severe storms, volcanic activity, coastal wave attack, and wildfires, can produce slope instability leading to landslides, a major geological hazard. Landslide danger may persist while emergency personnel are attempting rescue.

University Of Palestine 2009, Dr. Mohammed Ajjour

Volcanoes Very damaging phenomenon to people living in close vicinity to

eruption area. At present about 1000 volcanoes are active, especially in South East

Asia and USA Most volcanoes area are connected to boundaries of colliding plates

(like in Pacific)or in situations when plates move apart under Oceans. About 80% of earth’s surface, the seafloor as well as the land,

began as molten rock that rose from deep inside the earth. Can be beneficial as sources of fertile new soil, chemicals,

geothermal Energy and minerals.

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University Of Palestine 2009, Dr. Mohammed Ajjour

A Volcano is an outlet on ground surface for melting rocks , gases , water and heat emerging from the asthenosphere .

These compounds , the Magma , are first

contained in Magma Chamber before it is released.

Lava describes the melted liquid part of rocks which lost all his gaseous components.

Con. The Volcanoes 35

00 Million years ago some simple species of Bacteria were found, which are able to exist in absence of O2 and to photosynthesise CO2 to produce free oxygen. Some of these are still there.

Since the last 550 million years, the concentration of free O2 increased to present level allowing the existence of other species presence of Oxygen. At present ,these Species are undergoing different changes and adaptations..

During this long history ,the geological processes produced the minerals ( like Gold, diamond, phosphate, Iron...etc)and Fossile Energy Sources ( Oil, Coal, gas ).

Con. The Volcanoes Hazards and impacts :(primary) Lava flow. Pyroclastic activity Emissions of poisonous Gases.

Hazards and impacts :(secondary & tertiary )

Flow of volcanic Mud Floods Tsunamis and Earthquakes Atmospheric effects ( temperature, ..). Famines and diseases

University Of Palestine 2009, Dr. Mohammed Ajjour