hazards resulting from tectonic processes Flashcards
causes of tsunamis
displacement of water triggered by tectonic activity (earthquake or volcanic eruption) or a submarine landslide
how do tsunamis rapidly increase in height?
when shallow water is reached, the water is pushed upwards and can reach heights of 25m
What changes the impacts of tsunamis?
Height of the waves
distance travelled
Length of source event
warning or no warning
physical geography of the coastline
Coastal land use & population density
Distribution of tsunamis?
90% are generated in the Pacific Ocean
factors affecting
landslides
moisture content of the land
topography of the land
geology of the land
climate
cause of earthquakes
friction along plate boundaries builds up in the lithosphere and when this strength is overcome, they fracture along faults sending a series of seismic shockwaves to the surface
types of seismic shockwaves
P-waves
S-waves
L-waves
R-waves
Which seismic waves always occur
P-waves
S-waves
how do L-waves cause the most damage?
with a side to side movement across the surface
why do R-waves need loose material?
for rolling motions to occur from the low frequency
measuring the magnitude of earthquakes
Richter scale
Moment magnitude
Mercalli
impacts of seismic activity, shaking, can depend upon
population density
magnitude
depth of earthquake
distance from epicentre
design and strength of buildings
education/preparation
secondary impacts of earthquakes
flooding
fires
landslides
tsunamis
is predicting earthquakes possible?
no, but monitoring is
what do you monitor for an earthquake?
Foreshocks - series of minor shocks
Radon gas - decrease sharply before
Groundwater levels - rises before
spatial distribution of volcanic hazards
75% on the pacific ring of fire
5% on hotspots
hazards and their tectonic boundaries
earthquakes at all
no volcanoes at transform
volcanoes are linear to the boundary, earthquakes have a larger spatial distribution
classification of volcanic eruptions
Icelandic
Hawaiian
strombolian
vulcanian
vesuvian
Plinian
pelean
features of an Icelandic eruption -
fluid basalt magma
eruption from fissures and mid-ocean ridges
features of a Hawaiian eruption -
fluid basalt magma
from single vents in volcanoes
features of Strombolian eruption -
less fluid magma and gasses 1km
moderate explosion
frequent activity
features of vulcanian eruption -
viscous magma which solidifies fast turning into ash and cinders
violent
ash cloud 5km high and shaped like a cauliflower
features of a vesuvian eruption -
viscous magma with a high gas content
violent eruptions sends a wide, 25km tall ash cloud into the stratosphere
features of a Pelean eruption -
highly viscous magma
erupts out of weaknesses in the geology
15km ash cloud
pyroclastic flows down the side
features of a Plinian eruption -
gas ash and pumice ‘magma’
violent gas explosion
narrow cloud 30km into the stratosphere
types of magma flow
Pahoehoe
A’a
Blocky
Pillow
how are volcanic eruptions classified
VEI
Volcanic
Explosivity
Index
products of eruptions
Nuees ardentes
lava flows
mudflows
pyroclastic flows
ash fallout
gasses/acid rain
tephra
what are Nuees ardentes
a dense rapidly moving cloud of hot gasses ashes and lava fragments. a type of pyroclastic flow
what is tephra
rock fragments ejected during the eruption
how to manage volcanic risk
evacuation
hazard mapping
trenches and walls
observation of gas, temp, deformations, melting of snow % ice, magnetism
type of monitoring on the white island volcano
careful as it is capable of erupting violently and frequently
is a tourist destination - day trips
digital cameras are pointing into the crater, which are connected to satellites
how is predicting volcanic eruptions not always successful
insufficient action from authorities
lack of compliance with evacuation
unexpected/early
wind direction change
Hotspots occur…
due to the radioactive decay in the Earth’s core generating hot spots, which heat the lower mantle and create localised thermal currents where mantle plumes of magma rise vertically
how are super volcanoes formed?
when hotspots occur under continents, as the magma gets stuck and pools, melting the rock around for thousands of years. Over thousands of years the pressure builds up and when the eruption eventually happens it drains the magma lake and the land above collapse down over, creating a caldera
