GEOG exam 3

Tsunamis are

Large wave produced by the sudden vertical displacement of ocean water.

Meaning of Tsunami

Japanese for harbor wave

What is the most common trigger for tsunamis

Large earthquakes causing seafloor uplift or subsidence

What are other triggers for tsunamis

• underwater landslides

• volcano collapse

• submarine volcanic explosion

• asteroids

What is the Tsunami velocity formula

Depends on water depth (deeper water = faster wave)

Tsunami speed in open ocean

about 400-600mph

Tsunami amplitude in open ocean

very small; often unnoticed by ships

What happens as tsunami approaches shore?

Speed decreases, wave height increases.

Runup

vertical height tsunami reaches on land

Local tsunami

hits nearby coast after formation

Distant Tsunami

travels far across ocean before hitting land

plate setting producing most tsunamis

subduction zones

why transform faults rarely cause tsunamis

no vertical displacement of seafloor

2005 Indonesian tsunami cause

M9 mega-thrust earthquake in subduction zone

Why many died in 2004 tsunami

lack of warning system and education

1958 Lituya Bay tsunami cause

landslide triggered by earthquake

Lowest tsunami risk region

gulf of mexico

Why sailors don’t notice tsunamis

Low amplitude and long wavelength in open ocean

What happens as a tsunami nears land?

The height of the waves increases due to a decrease in
both water depth and tsunami velocity.

Which of the following describes the tsunami in
Indonesia in 2004?

M 9 earthquake triggered a 10 m tsunami, which was the
deadliest tsunami ever, killing more than 200,000 people in several
countries.

Why do sailors rarely notice a tsunami passing in
the open ocean?

Tsunamis are too small in amplitude in the open ocean, and the distance between crests is too large to notice its passing.

What is the difference between a distant tsunami and local tsunami?

Distant tsunamis move farther from their source before they hit land

Where volcanoes occur

Convergent boundaries, divergent boundaries, host-spots

Where volcanoes usually don’t occur

Transform boundaries and continent- continent collisions

Ring of fire

region around Pacific Ocean with many volcanoes

Magma

molten rock beneath Earth’s surface

Lava

Magma that reaches the surface

Three types of magma

• Basaltic

• Andesitic

• Rhyolitic

Basaltic magma

low silica, low viscosity, effusive eruptions

Andesitic magma

Intermediate silica and viscosity

Rhyolitic magma

high silica, high viscosity, explosive eruptions.

Viscosity

resistance to flow.

Effect of silica on viscosity

more silica = higher viscosity (more rock in it, the more resistant it is to flow)

Effect of temperature on viscosity

cooler magma = higher viscosity

Volatiles

dissolved gases in magma

High volatile content

more explosive volcanic erruptions

Low volatile content

effusive eruption

Effusive Eruption

lava flows, low viscosity magma

Explosive eruption

Ash, pyroclastic debris, high gas pressure

Pyroclastic debris

volcanic ash and rock fragments ejected explosively

Stratovolcano

High viscosity magma, explosive eruptions

Shield volcano

Low viscosity basaltic lava, broad shape

Cinder cone

Built from volcanic fragments (scoria)

Lava dome

very viscous magma forming dome shape

Continental caldera

large collapse after massive explosive eruption

Most dangerous volcano type

stratovolcano

Mauna Loa

shield volcano

Mt st Helens

Stratovolcano

Why stratovolcano are dangerous

Because of the high viscosity magma, explosive eruptions debris

Landslide

Downward movement of rock or soil due to gravity

Factors increasing landslide risk

steep slopes,

water saturation,

earthquakes,

weak materials

Rockfall

Free falling rock from steep slopes

Debris flow

fast-moving mixture of water and sediment

mudflow

water-rich flow of fine sediment

Creep

very slow slope movement

Slump

rotational movement along curved surface

Most common landslide trigger

heavy rainfall

other triggers for landslides

• earthquakes

• volcanic activity

• human activity

ways to reduce landslides

drainage control, vegetation, retaining walls