geological disasters - earthquakes and volcanic eruptions
Earthquakes
Earthquakes are the result of a sudden release of energy from the earth's crust that causes seismic waves that can be in the form of vibrations, shaking or earth crust movements. The Earth's outer layer is broken into pieces called tectonic plates, these are constantly moving towards, away from or past each other. An earthquake occurs when crust breaks and move as a result of stresses caused by tectonic plate movements.
Most earthquakes occur on the rim of tectronic plates, where one plate is forced under another.
Earthquakes are measured using observations from seismoeters and are measured using a scale starting at 1. Earthquakes with a magnitude 7 and over potentially can cause serious damage over larger areas. The largest earthquakes in history had a magnitude slightly over 9, although there is no limit to the possible magnitude. Earthquakes have an epicentre or centrepoint and when this is located offshore, the seabed may be displaced enough to cause a Tsunami. Earthquakes can also set off landslides and sometime volcanic activity. Earthquakes can cause significant destruction to built structures and man made environments.
Most earthquakes occur on the rim of tectronic plates, where one plate is forced under another.
Earthquakes are measured using observations from seismoeters and are measured using a scale starting at 1. Earthquakes with a magnitude 7 and over potentially can cause serious damage over larger areas. The largest earthquakes in history had a magnitude slightly over 9, although there is no limit to the possible magnitude. Earthquakes have an epicentre or centrepoint and when this is located offshore, the seabed may be displaced enough to cause a Tsunami. Earthquakes can also set off landslides and sometime volcanic activity. Earthquakes can cause significant destruction to built structures and man made environments.
Volcanic eruptions
Volcanic Eruptions are when various gases, ash and or magma are expelled from the earth via a volcanic vent or fissure. There are two types of volcanic eruptions, Explosive and Effusive. Explosive eruptions spew ash, gas and lava into the air as a result of massive pressure build up, Effusive eruptions result in a more steady outflow of lava and can flow like molten lava rivers sometimes for years. While many eruptions only pose dangers to the immediately surrounding area the biggest eruptions can have larger regional impacts, such as large amounts of ash in the atmosphere preventing air flights.
In 1980 a volcano erupted at Mount St Helens, Washington, USA, for two months before the major eruption there were many small temors and steam venting events. The eruption was large and ash was deposited in eleven states. 57people died and hundreds of kilometers were reduced to wasteland. Mount St. Helens was left with a crater on its north side.
In 1980 a volcano erupted at Mount St Helens, Washington, USA, for two months before the major eruption there were many small temors and steam venting events. The eruption was large and ash was deposited in eleven states. 57people died and hundreds of kilometers were reduced to wasteland. Mount St. Helens was left with a crater on its north side.