lecture 15: geohazards ii

earthquake scaling

used to estimate earthquake probabilities with relationship

What can hazards maps be used for?

to build safely around earthquake areas

prioritise aid to areas in red

tsunami

earthquake in oceans

measure of tsunami

speed of wave is proportional to square root of water depth

distribution of earthquakes

mainly at plate boundaries

• mid-ocean ridges

• subduction zones

80% activity happens under ocean

Mid-ocean ridges

volcanoes grow in shallow water → water turns to superheated stream and explosive eruptions

• eruptions under glaciers => flash floods

Volcanoes at subduction zones

small amount of melting of oceanic plate in mantle → reaches surface = volcano

often explosive due to higher volatiles + high silica content

forms volcanic arc islands

Hazards of volcanoes

• eruption cloud - acid rain

• pyroclastic flow

• lahar

• landslides

• lava flow

• flash flood

• melting of glaciers

risk management for volcanoes

• to know where it will happen

• building that won’t prevent damage

• predicitability f volcanoes

How to monitor volcanoes?

• tilt

• seismic signals

• gravity changes

• deformation

• fluid chemistry

• gas output