Natural Disasters and Plate Tectonics (L33) Flashcards
What is an important thing to keep in mind about natural disasters associated with geological processes?
they are natural
What is an earthquake?
A sudden release of stored energy caused by slip along a fault or fracture in the earth
What are major earthquakes caused by?
Slow deformation and buildup of energy between tectonic plates
What is the Focus?
the point of energy release or rupture underground
How is energy built up and then released?
we start with rocks on both sides of an existing fault that are deformed by tectonic forces
once frictional forces along the fault are overcome, slippage occurs at the weakest point (the focus)
an earthquake occurs due to this release of energy as seismic waves when the deformed rocks springs back to its original shape (elastic rebound)
What 2 categories do Seismic waves belong to?
Body waves that travel through the material
Surface waves that travel on Earth’s surface and produce most of the shaking
What are the 2 types of body waves?
Primary (P) waves have a push-pull
Secondary (S) waves are characterized by shear motion at right angles to their direction of travel
What difference do P waves and S waves have in traveling?
P waves travel through all states of matter
S waves travel only through solids
What are the 2 surface waves that travel on the surface?
Rayleigh waves - move in a rolling motion
Love waves - move side-to-side
What instrument is used to record seismic waves?
Seismometer
What is the graphic representation of the detedction of seismic waves by a seismometer?
Seismograph
How do you determine the distance between the recording station ad the earthquake’s epicentre?
Differences in the arrival times of these waves at different recording stations
longer the time diff betewen the arrival of hte first P waves and the arrival of the first S waves, the greater the distance between the recording station and the earthquake epicentre
about 95% of the energy released by earthquakes is focused along _____
Plate boundaries
What is magnitude?
basically is a quantitative measure of the amount of energy released during an earthquake
What is Richter magnitude?
A concept where units of magnitude are based on the amplitude (wave height) of the largest seismic waves recorded, and also accounts for the decrease in wave amplitude with increased distance from the epicentre
Where does the word tsunami come from?
Japanese “tsu”, meaning harbour and “nami” meaning wave
How do Tsunamis result?
result from a signficant vertical displacement of water due to the slip of a fault located on the ocean floor, a large undersea landslide triggered by an earthquake, or other disturbances
How is a tsunami caused in detail?
the plate is bulging upward due to being deformed from being stuck to the subducting plate
when the plate becomes unstuck, it snaps back into an unstressed state and displaces a large amount of water at once, producing a large wave
When do tsunamis become destructive?
when they travel into shallow water, due to there being friction between the moving water and the sea floor
Why is the Japanese Tsunami termed a triple disaster?
because it included an earthquake, a tsunami and a nuclear meltdonw
What is an imprtant step to reduce damage from tsunami?
the installation of warning systems as it can take hours for tsunami to reach distant shores
Where do most volcanoes occur along?
plate tectonic boundaries
why do volcanoes associated with mafic magmas erupt relatively gently?
they have a low viscosity (runny) due to low silica content and low gas content
Why do volcanoes with intermediate to felsic magma tend to erupt explosively?
b/c they have high viscosity (stiff and gooey) due to high silica content and hvae high gas content
What is a caldera?
the crater produced by a collapse of the top of the volcano as it is so violent and explosive
How do explosive eruptions lower the amount of solar radiation reaching Earth’s surface?
explosive eruptions emit huge quantities of gases and fine-grained ash into the atmosphere which filter out and reflect a portion of the incoming solar radiation back into space
What does sulphur doxide do during a volcanic eruption?
changes into sulphate aerosols, which are liquid particles that reflect sunlight and keep some of the warmth from reaching Earth’s surface
How is volcanism tied to the art piece The Scream?
Munch the artist of the piece was inspired by the blood red sky he saw and drew it on the painting
this red sky was due to the volcano Krakatau exploding and Munch witnesse the fiery sunsets created from it
