natural hazards (mods 1-6)

earthsci 105 mid sem test 2026 s2

seismic wave type that can travel through fluids

p-waves

seismic wave type that can only travel through solids

s-waves

earth's layers in order from outermost to innermost

lithosphere, asthenosphere, mantle, liquid core, solid core

mechanical layers of the earth

lithosphere and asthenosphere

compositional layers of the earth

mantle, liquid core, and solid core

the thin, ductile layer that allows tectonic plates to move

the asthenosphere

hazards that characterise convergent boundaries between oceanic and oceanic crust

extreme earthquake, tsunami, and volcanic hazards

a currently active example of continent-continent collision, and the hazards it produces

the himalayas: associated hazards are earthquakes and landslides

type of fault is associated with compressive forces

a reverse (thrust) fault

explains the spatial distribution of earthquake and volcano hazards

lithospheric plate boundaries

earthquakes occur when…

when elastic strain in rocks adjacent to a fault zone exceeds frictional strength along the fault

what happens to a tsunami's wavelength, wave height, and wave speed as it approaches land?

wavelength decreases, wave height increases, and wave speed decreases

a tsunami’s wave speed … as it approaches land

wave speed decreases

a tsunami’s wave height … as it approaches land

wave height increases

a tsunami’s wavelength … as it approaches land

wavelength decreases

how fast do tsunami waves travel in the deep ocean?

approximately 700 km/hr

tectonic settings most at risk of generating high-magnitude earthquakes and tsunamis

convergent collision settings at ocean-ocean and ocean-continent plate boundaries

can you recognise an arriving tsunami just because it has a large bore or breaking waves?

no, you cannot rely on this to recognise a tsunami

why would a magnitude 7.0 earthquake in california cause less structural damage than one in the middle east?

due to differences in building codes (california has stronger building codes than the middle east)

after a large magnitude earthquake, how did simeulue and banda aceh move relative to their original elevations?

due to subduction, simeulue moved up and banda aceh moved down

what made the chile 1960 event historically significant?

it was the largest magnitude earthquake ever recorded (mw 9.5) and generated a tsunami that killed people across an entire ocean basin

characteristics of shield volcanoes

effusive lava flows created by low viscosity magma

characteristics of composite/stratovolcanoes

layers of explosive and effusive eruptions forming shallow, broad flanks with a steeper cone-shaped vent

characteristics of scoria cone volcanoes

small, formed by short-lived volcanic activity, made up of unconsolidated pyroclastic material standing at the angle of repose

decompression melting

rock is kept at a high temperature while the pressure is reduced

flux melting

volatiles are added to a solid rock to decrease the melting temperature

heat-transfer melting

heat moves from a source into rocks that melt at a lower temperature

what dominantly controls volcanic eruption style?

the viscosity of the erupted magma: low viscosity fluids flow more easily than high viscosity fluids

what increases viscosity?

cooling

what lowers viscosity?

heating

pillow lavas indicate that a volcanic eruption …

… that a volcanic eruption happened underwater

why is rhyolitic magma more viscous than basaltic magma?

it has more silica tetrahedra by weight percent (they link together, making them very strong)

weight percent of silica tetrahedra in rhyolitic magma

65% to 75%

weight percent of silica tetrahedra in basaltic magma

45% to 55%

what magma properties lead to the most explosive type of eruption?

high viscosity combined with high gas content

a fluid with low viscosity …

… flows easily

magma generation processes

decompression melting, fluid-induced (flux) melting, and increasing temperature (heat-transfer melting)

the most common cause of volcano fatalities since 1500AD are …

… pyroclastic flows and surges

the three parts of an eruption column, from bottom to top

gas thrust region (bottom), convective thrust region (middle), umbrella cloud (top).

bottom of an eruption column

gas thrust region

middle of an eruption column

convective thrust region

top of an eruption column

umbrella cloud

what is a lahar?

a volcanic debris flow that may occur with or without volcanic activity

does a sophisticated volcano monitoring system guarantee no disaster will occur?

no, it can still occur; monitoring simply lowers the risk

possible precursors to a volcanic eruption

surface heat flow increase, seismic activity, gas composition changes, surface inflation, magnetic or electrical field changes

carbon dioxide is …

… denser than air