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Geohazards

Geohazards. Earthquakes. Effects. Ground shakes violently. Liquifaction – soft sediment turns to liquid. Buildings and roads collapse, pipes break, sewage/gas leaks cause fire and disease. Liquifaction – soft sediment turns to liquid. Tsunamis if earthquake beneath the sea.

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Geohazards

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  1. Geohazards Earthquakes Effects • Ground shakes violently • Liquifaction – soft sediment turns to liquid • Buildings and roads collapse, pipes break, sewage/gas leaks cause fire and disease • Liquifaction – soft sediment turns to liquid • Tsunamis if earthquake beneath the sea

  2. Death Valley – Big Fault Zone (earthquake zone)

  3. Geohazards Earthquakes Prediction to Reduce Risk • Gas emissions • Foreshocks (minor tremors) – seismic graphs • Ground changing (tiltmeters) • Change in water levels (seen in wells) • Periodicity – gaps between earthquakes

  4. Sometimes, animals act strangely before an Earthquake

  5. Explosive Volcanic Eruptions Volcanic Hazards Effects • Ash fall – collapsing building roofs • Blast – explosion itself can be destructive • Pyroclastic Flow (nuee ardente) – cloud of very hot dust and gas flowing very fast down side of mountain • Mud flow (lahar) – water mixes with ash producing a runny mud, moves less fast than pyroclastic flows • Volcanic gas – poisonous produced during the eruption • Lava flows – slower moving than effusive due to visocity

  6. Effusive Volcanic Eruptions Volcanic Hazards Effects • Volcanic gas – poisonous produced during the eruption • Lava flows – slow moving but can destroy property

  7. Volcanic Prediction to Reduce Risk Before the eruption, the magma rises: • Gases lost, minor earthquakes, heat flow increases, side of mountain changes slope (tiltmeter) Historic records – showing frequency Controlling • Diverting lava flows with barriers • Planning evacuation of hazardous areas • Spraying lava to make it solidify

  8. Landslides Effects Mass movement of rock and soil under gravity Triggered by earthquake, slope instability or meteorite Water is a major factor – lubricates the sliding plane Controlling Monitor with measurements of fixed points – have they moved Reduce by: Planting trees to bind sediment, drain water from soil, build walls to contain any landslide

  9. India Smashing into Tibet to Create the Himalayas Darjeeling

  10. Tsunami – Caused by Earthquakes or Landslides

  11. Landslides – Gravity, Earthquake, Monsoon and Volcanic Activity Triggers Bangladesh Colorado USA

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