OA: Volcanoes, Earthquakes, & Tsunamis

hotspot

upwelling through Earth’s mantle, causing mantle to melt and magma to be produced

What percentage of the world’s volcanoes form at subduction zones?

80%

high viscous magma

at subduction zones

erupt explosively

classical shape

low viscous magma

at hotspots

effusive eruptions

shield volcanoes

Direct volcanic hazards

• explosive blasts

• lava

• pyroclastic flow

indirect volcanic hazards

• dust - sulphuric acid

• acid rain

• lahars

• landslides

What was the eruption at Mt St. Helen caused by?

1980

landslide release pressure inside the magma chamber suddenly creating a lateral blast

lava flows

moving bodies of molten rock

What does the speed of lava flows depend on?

1. type of lava and viscosity

2. steepness of ground

3. whether lava confined to a channel

4. rate of lava production at vent

low viscosity

• Travels tens of kms

• 10km/hr on steep slopes

High viscosity

• slower

• reach few kms

main hazards of lava flows

property and infrastructure damage

Pyroclastic flows

volcanic ash columns collapse due to explosion of volcanic vent wh

What are pyroclastic flows made of?

rock, ash, hot gases

basal layer

large blocks of rocks moving along ground

Example of deadly pyroclastic flow

Vesuvius AD79

lahars

extremely hazardous event that involves a mixture of water and rock fragments travelling rapidly down slope of volcanow

hat triggers lahars

• eruptions

• heavy rainfall

• earthquake

• breaking of crater lake

where do lahars typically form?

stratovolcanoes

how do lahars flow

• through low topographical areas

• hundreds of m wide

• tens of m deep

• moves at ten of m per second

Lahar hazard mitigation

• rapid evacuation by prior plans

  • upstream monitors and alarm systems

example of deadly lahar

Mt. Ruapehu, New Zealand

18th March 2007

Mt Rainer Lahar Hazard

• highest volcano in Cascade Mountain Range - 4392m

• large amount of glacial ice

• dangerous due to large population situated within lahar hazard zone in valley - Tacoma and Seattle

Volcanic Eruptions caused by climate change

ice melting cause decompression melting → water increase rate of weathering → weathering weakens rocks and makes landslide more likely → landslides release pressure causing eruption

How do earthquakes occur?

energy stored in elastically strained rocks is suddenly released, causing ground shaking and sending seismic waves

fault

rock fracture where 2 sides have been displaced relative to each other

tensional/extension

pulling apart

shear force

strike-slip fault

seismograph

detects and records earthquakes and other ground motion

Body waves

through interior of Earth

ray that leaves earthquake and travels to recording station

Primary waves (P)

Compressional waves that move rock particles apart and back together in the direction the wave is traveling.

• travel through solid and liquid

• fastest seismic waves

Secondary Waves (S)

Shear waves cause vibrations that are perpendicular to the direction the waves are traveling through the rock.

• don’t travel through liquids

• slower than P waves

Surface waves

travel over Earth’s surface

slower, arriving after both P and S waves

Cause most damage

Earthquakes caused by climate change

Major glaciation

sea levels rise causing increased pore pressure of fluids and cause ruptures creating earthquakes