E-Learning Geography E-Learning Geography projectproject

EarthquakesEarthquakes

SeaquakesSeaquakes

VolcanoesVolcanoes

EarthquakesEarthquakes An earthquake is a sudden movement of the An earthquake is a sudden movement of the

Earth, caused by movement between tectonic Earth, caused by movement between tectonic plates. For hundreds of millions of years, the plates. For hundreds of millions of years, the forces of plate tectonics have shaped the Earth as forces of plate tectonics have shaped the Earth as the huge plates that form the Earth's crust slowly the huge plates that form the Earth's crust slowly move over, under, and past each other. move over, under, and past each other. Sometimes the movement is gradual. At other Sometimes the movement is gradual. At other times, the plates are locked together, unable to times, the plates are locked together, unable to release the accumulating energy. When the release the accumulating energy. When the accumulated energy grows strong enough, the accumulated energy grows strong enough, the plates break free causing an earthquake. If the plates break free causing an earthquake. If the earthquake occurs in a populated area, it may earthquake occurs in a populated area, it may cause many deaths and injuries, cause many deaths and injuries, and extensive and extensive property damage.property damage.

What causes earthquakes?What causes earthquakes?         The short answer is that earthquakes are caused by faulting, a sudden lateral or The short answer is that earthquakes are caused by faulting, a sudden lateral or

vertical movement of rock along a rupture (break) surface. vertical movement of rock along a rupture (break) surface.     Here's the longer answer: The surface of the Earth is in continuous slow motion. This is     Here's the longer answer: The surface of the Earth is in continuous slow motion. This is plate tectonics--the motion of immense rigid plates at the surface of the Earth in plate tectonics--the motion of immense rigid plates at the surface of the Earth in response to flow of rock within the Earth. The plates cover the entire surface of the response to flow of rock within the Earth. The plates cover the entire surface of the globe. Since they are all moving they rub against each other in some places (like the San globe. Since they are all moving they rub against each other in some places (like the San Andreas Fault in California), sink beneath each other in others (like the Peru-Chile Trench Andreas Fault in California), sink beneath each other in others (like the Peru-Chile Trench along the western border of South America), or spread apart from each other (like the along the western border of South America), or spread apart from each other (like the Mid-Atlantic Ridge). At such places the motion isn't smooth--the plates are stuck together Mid-Atlantic Ridge). At such places the motion isn't smooth--the plates are stuck together at the edges but the rest of each plate is continuing to move, so the rocks along the at the edges but the rest of each plate is continuing to move, so the rocks along the edges are distorted (what we call "strain"). As the motion continues, the strain builds up edges are distorted (what we call "strain"). As the motion continues, the strain builds up to the point where the rock cannot withstand any more bending. With a lurch, the rock to the point where the rock cannot withstand any more bending. With a lurch, the rock breaks and the two sides move. An earthquake is the shaking that radiates out from the breaks and the two sides move. An earthquake is the shaking that radiates out from the breaking rock. breaking rock.     People have known about earthquakes for thousands of years, of course, but they     People have known about earthquakes for thousands of years, of course, but they didn't know what caused them. In particular, people believed that the breaks in the didn't know what caused them. In particular, people believed that the breaks in the Earth's surface--faults--which appear after earthquakes, were caused *by* the Earth's surface--faults--which appear after earthquakes, were caused *by* the earthquakes rather than the cause *of* them. It was Bunjiro Koto, a geologist in Japan earthquakes rather than the cause *of* them. It was Bunjiro Koto, a geologist in Japan studying a 60-mile long fault whose two sides shifted about 15 feet in the great Japanese studying a 60-mile long fault whose two sides shifted about 15 feet in the great Japanese earthquake of 1871, who first suggested that earthquakes were caused by faults. Henry earthquake of 1871, who first suggested that earthquakes were caused by faults. Henry Reid, studying the great San Francisco earthquake of 1906, took the idea further. He said Reid, studying the great San Francisco earthquake of 1906, took the idea further. He said that an earthquake is the huge amount of energy released when accumulated strain that an earthquake is the huge amount of energy released when accumulated strain causes a fault to rupture. He explained that rock twisted further and further out of shape causes a fault to rupture. He explained that rock twisted further and further out of shape by continuing forces over the centuries eventually yields in a wrenching snap as the two by continuing forces over the centuries eventually yields in a wrenching snap as the two sides of the fault slip to a new position to relieve the strain. This is the idea of "elastic sides of the fault slip to a new position to relieve the strain. This is the idea of "elastic rebound" which is now central to all studies of fault rupture.rebound" which is now central to all studies of fault rupture.

Earthquakes can cause severe and Earthquakes can cause severe and widespread damage to weak buildings widespread damage to weak buildings or structures, or to those located on or structures, or to those located on ground subject to fault breakage, ground subject to fault breakage, strong shaking, or landsliding. The slip strong shaking, or landsliding. The slip (movement) on the fault may break the (movement) on the fault may break the surface of the Earth, offsetting roads surface of the Earth, offsetting roads and tearing apart buildings or pipelines and tearing apart buildings or pipelines built across the fault. Such damage can built across the fault. Such damage can be spectacular, but it is limited to the be spectacular, but it is limited to the vicinity of the fault.vicinity of the fault.

History of earthquakes.History of earthquakes. Earthquakes have been recorded as early as 1177 B.C. Earthquakes have been recorded as early as 1177 B.C.

in China. Of course earthquakes have been a part of in China. Of course earthquakes have been a part of myth and legend since the dawn of man. In myth and legend since the dawn of man. In Greek Greek MythologyMythology, Posseidon (Neptune in the , Posseidon (Neptune in the Roman Roman pantheonpantheon) was "God of the Sea". Yet one of his ) was "God of the Sea". Yet one of his powers was thought to be that of "earth shaker". As a powers was thought to be that of "earth shaker". As a tsunami is often the result of an earthquake, this was tsunami is often the result of an earthquake, this was an appropriate power for a sea god.an appropriate power for a sea god.

In In European historyEuropean history, the earliest recorded earthquake , the earliest recorded earthquake occurred in 580 B.C. In North America the great occurred in 580 B.C. In North America the great earthquakes of 1811-1812 occurred near New Madrid, earthquakes of 1811-1812 occurred near New Madrid, Missouri. The magnitude of the quakes are not known, Missouri. The magnitude of the quakes are not known, but they are estimated to have been about 8 on but they are estimated to have been about 8 on theRichter scale. There were actually three large theRichter scale. There were actually three large quakes with aftershocks between and for months after. quakes with aftershocks between and for months after. The quake was so wide-spread it was felt as far away The quake was so wide-spread it was felt as far away as Boston.as Boston.

Who was the Roman god of Who was the Roman god of earthquakes?earthquakes?

Neptune (Poseidon in Greece) was Neptune (Poseidon in Greece) was the Roman god of earthquakes and the Roman god of earthquakes and the sea.the sea.

When an earthquake happens in the When an earthquake happens in the ancient times, people thought that ancient times, people thought that Neptune is angry with them, so they Neptune is angry with them, so they offer sacrifices.offer sacrifices.

What happens during an What happens during an earthquake.earthquake.

Earthquakes occur because friction holds the rock Earthquakes occur because friction holds the rock masses on either side of the fault together, masses on either side of the fault together, while plate motion slowly bends and stretches while plate motion slowly bends and stretches the rock, storing energy much like the energy the rock, storing energy much like the energy stored in a stretched rubber band. An individual stored in a stretched rubber band. An individual earthquake occurs when the stored energy earthquake occurs when the stored energy

becomes greater than the friction, and the rock becomes greater than the friction, and the rock masses suddenly slip along the fault. Much of masses suddenly slip along the fault. Much of

the energy stored in the stretched rock is the energy stored in the stretched rock is released in seismic waves, which travel out in released in seismic waves, which travel out in all directions from the fault on which the all directions from the fault on which the earthquake occurre.earthquake occurre.

What happens after an What happens after an earthquake.earthquake.

Our earth is made of many layers just like an Our earth is made of many layers just like an onion. We can divide it into four main layers: onion. We can divide it into four main layers: the inner or solid core, the outer or liquid core, the inner or solid core, the outer or liquid core, mantle, and crust. The inner core is  composed mantle, and crust. The inner core is  composed mostly of iron and is extremely hot. This heat mostly of iron and is extremely hot. This heat causes the outer core to remain in a liquid or causes the outer core to remain in a liquid or molten form. molten form. 

Most of the earth's mass is in the mantle. But if Most of the earth's mass is in the mantle. But if pressure were to be applied on this layer, it pressure were to be applied on this layer, it deforms slowly. The crust is the thinnest layer deforms slowly. The crust is the thinnest layer and is rocky. It is also the coldest layer and is rocky. It is also the coldest layer relatively. Because it is cold, the layer is also relatively. Because it is cold, the layer is also brittle and fractures easily during an brittle and fractures easily during an earthquake.  earthquake. 

How are volcanoes created.How are volcanoes created. Volcanoes are formed usually near plate boundaries, most Volcanoes are formed usually near plate boundaries, most

commonly divergent/constructive plate boundaries, such as the commonly divergent/constructive plate boundaries, such as the Mid-Atlantic Ridge. Here the crust is moving apart and causing Mid-Atlantic Ridge. Here the crust is moving apart and causing melting due to a decrease in pressure. The magma rises, filling melting due to a decrease in pressure. The magma rises, filling the cracks in the crust and forms fissure volcanoes and sea the cracks in the crust and forms fissure volcanoes and sea mounts, which are submarine volcanoes. mounts, which are submarine volcanoes. 

Volcanoes also form at convergent/destructive boundaries, like Volcanoes also form at convergent/destructive boundaries, like the the rim of the Pacific ocean known as the Ring of Fire, which the the rim of the Pacific ocean known as the Ring of Fire, which contains about 68% of Earth's subaerial volcanoes. A volcano here contains about 68% of Earth's subaerial volcanoes. A volcano here is formed when a denser, colder oceanic plate, subducts under is formed when a denser, colder oceanic plate, subducts under another plate, either a continental or warmer oceanic plate. The another plate, either a continental or warmer oceanic plate. The subducted plate will melt under the high temperatures in the subducted plate will melt under the high temperatures in the mantle. This will form magma, which will in turn form cracks in the mantle. This will form magma, which will in turn form cracks in the plates, which allows the magma to flow out from the mantle into plates, which allows the magma to flow out from the mantle into the crust and sometime onto Earth's surface. The lava (when the crust and sometime onto Earth's surface. The lava (when magma reaches the surface it is called lava) will then harden and magma reaches the surface it is called lava) will then harden and form layers, slowly forming a volcano. form layers, slowly forming a volcano. 

What causes a seaquake.What causes a seaquake. Basically, the process is identical to an earthquake on Basically, the process is identical to an earthquake on

land. The Earth's crust is made up of Plates, which land. The Earth's crust is made up of Plates, which move against each other. Sometimes they get stuck, move against each other. Sometimes they get stuck, resulting in a build-up of pressure which eventually resulting in a build-up of pressure which eventually breaks the obstruction. It the sudden release of this breaks the obstruction. It the sudden release of this pressure, that causes an Earthquake. The only pressure, that causes an Earthquake. The only difference with a Seaquake, is that this happens difference with a Seaquake, is that this happens underwater, on the Seabed. underwater, on the Seabed. 

The major problem with Seaquakes, are their The major problem with Seaquakes, are their secondary effects, the vibration and shockwaves can secondary effects, the vibration and shockwaves can displace a large volume of water, which becomes a displace a large volume of water, which becomes a Tidal Wave or TsunamiTidal Wave or Tsunami..

A tidal wave.A tidal wave. A tsunami) is a series of waves, made in an ocean or A tsunami) is a series of waves, made in an ocean or

other body of water by an other body of water by an earthquakeearthquake, landslide, , landslide, volcanic eruptionvolcanic eruption, or , or meteorite impactmeteorite impact. Tsunamis can . Tsunamis can cause huge destruction when they hit coastlines. cause huge destruction when they hit coastlines. Some people call tsunamis “tidal waves”, but these Some people call tsunamis “tidal waves”, but these large waves really have little to do with tides, so the large waves really have little to do with tides, so the term “tidal wave” does not really suit them.term “tidal wave” does not really suit them.

Tsunami waves are different from the waves you can Tsunami waves are different from the waves you can usually find rolling into the coast of a lake or ocean. usually find rolling into the coast of a lake or ocean. Those waves are made by wind offshore and are Those waves are made by wind offshore and are quite small compared with tsunami waves. A tsunami quite small compared with tsunami waves. A tsunami wave in the open ocean can be more than 100 km wave in the open ocean can be more than 100 km across. That’s roughly the length of 1000 American across. That’s roughly the length of 1000 American football fields! Tsunami waves are huge and can football fields! Tsunami waves are huge and can travel very quickly, at about 700 km/hr, but they are travel very quickly, at about 700 km/hr, but they are only about one meter high in the open ocean.only about one meter high in the open ocean.