HAZARDS - volcanoes Flashcards
pyroclastic flow
mixture of hot rock, lava, ash and gasses which erupt from a volcano and move rapidly along the ground
tephra
rock fragments ejected during the volcanic eruption
nuée ardente
dense rapid moving cloud of ash, hot gasses and lava fragments - type of pyroclastic flow
primary hazards of a volcano
pyroclastic flow, lava flow, tephra, nuée ardente
secondary hazards of a volcano
acid rain, lahars, tsunamis
lahars
destructive mudflow - ash and other volcanic materials mixed with water.
spatial distribution of earthquakes
95% of plate boundaries are associated with constructive and destructive plate boundaries. 5% are intraplate.
what are the three factors that increase the viscosity of magma?
low temperature
high silica content
low volume of dissolved gas
what are the characteristics of high viscosity magma?
thick, cooler magma = violent eruptions as it blocks vents
what are the characterisitics of low wiscosity magma
hot, runny magma
less pressure so gasses can escape and vents are not blocked.
less violent eruptions
basaltic magma
-high temperature, low silica content = LOW viscosity =
-non-violent eruptions
-found at constructive plate boundaries
(balsamic vinagar is runny)
rhyolitic
-low temperature, high silica content =thick HIGH viscosity magma
-violent eruptions
-found at destructive margins
(Ryan is chilled out and slow)
andesitic
low temp, high silica = HIGH viscosity - VERY explosive - affects large areas - basaltic and continental crust at subduction zone - destructive margin (Andrea is even slower than Ryan)
how is the magnitude of volcanoes measured?
VEI volcano explosivity index 0-8 = based on the amount of material ejected and how high it is blasted.
frequency
depends on the volcano
- constructive - basaltic lava = frequent with smaller mag.
- destructive - rhyolitic lava = every 100,000 yrs with larger mag
predictability
volcanologists look at eruption history and current data
BUT impossible to predict magnitude, nature and timing.
seismometer and seismograph
measure seismic activity due to rising magma causing fracturing and cracking of overlying rock
tiltmeter, laser based electronic distance measurements
show ground deformation
magnetometer
measures upward movement of iron rich magma.
changing magnetism =rising magma
hydrolic instruments
measure increased water temp/ gas content
rising magma heats ground water and contaminates with gasses
remote sensing equipment
measures warning signs such as landslides, gas emission, small eruptions.
uses solar powered digital camera surveillance and thermal imaging in and around the main crater.
primary impact
occurs directly following the eruption
examples of primary impacts
lava and pyroclastic flow - destroy crops, infrastructure
ash fallout- damages crops, contaminates water
increased co2 and sulphur
deaths, injuries
secondary impacts
occur as a result of primary impacts - occur in days and weeks following the eruption
examples of secondary impacts
fertile soil economic loss from crop failure unemployment due to business failure shortages of resources - no transport lahars flooding acid rain phycological issues due to trauma and loss
short term response eg’s
evacuation, emergency services, try to block lava flow, shelters and evacuation camps
long term responses 4 categories
preparedness, mitigation, prevention and adaption
examples of long term responses
- investment in prediction and warning systems
- hazard map evacuation strategies
- stores of emergency food and water supplies.
