Hazards Flashcards
(26 cards)
State the three main secondary hazards of a volcanic eruption
Lahars, volcanic landslide, tsunami
State the three main primary hazards of a volcanic eruption
Lava flows, pyroclastic flows, tephra
Are lava flows life threatening?
Rarely
T/F
Rebuilding after destruction of lava flows is not possible
True
Rebuilding isn’t possible
What are the characteristics of basalt?
Runny and fast flowing
What are the characteristics of rhyolite?
Viscous and slow moving
What are pyroclastic flows? Are they a threat to humans?
Avalanches of hot ash, pumice, rock fragments and gas
Destroy everything and greatest threat to people - poisonous gases and fast flowing
Speeds of pyroclastic flows
100km h
What is tephra?
Fragments of volcanic rock that are blasted into the atmosphere by explosive eruptions
What are the impacts of tephra
Blankets landscape with many disruptions to economic activity
- roads impassable
- roof collapse
- crops smothered
- engine damage
What are lahars? Are they a threat to people?
Mudflows of volcanic material, second greatest threat to people after pyroclastic flows
Ash and debris can mix with water and then move rapidly
What can cause lahars?
Localised rainfall/electric storms caused by eruption events can trigger lahars.
May also be influenced by the collapse of a crater lake or rapid snow or ice melting
Where are Lahars most common?
River valleys and low lying areas
What can cause volcanic landslides?
Ground deformation of volcanic slopes by rising magma before an eruption or during
What does VEI stand for?
Volcanic explosivity index
How many levels are there to the VEI? With 0 being the highest or lowest?
0-8. Zero being the least explosive
How many hours would an eruption with a VEI of 3 have and would it be considered as non explosive, small, moderate, large or very large?
1-12 hours
Moderate/large
Stat human reasons why some volcanoes are more hazardous than others
- proximity to population
- major cities is more hazardous than remote area
- high pop density out large numbers of people at risk - trickier to control and evacuate - predictions forecasts and reactions
- monitoring
How can monitoring a volcano reduce the size of a hazard?
Creating warning and evacuation plans for people at risk
It can be beneficial to have evidence of past eruptions to suggest likely eruptive scenarios
How can the viscosity of magma have a direct impact on how hazardous a volcanic eruption is?
The more viscous the greater the potential for explosive eruptions
How can the material ejected vary the danger posed on a population from a volcanic eruption?
Non-explosive - lava flows = no serious hazard
Explosive = tephra or pyroclastic flows - ash can be carried further and have impact on further afield e.g. Aircraft etc
What are jökulhlaups and how do they form?
Large fast moving glacier-outburst floods
The form when a volcano erupts beneath a glacier
Name 4 impacts jökukhlaups can have
- difficulty of getting aid and emergency workers around
- debris can destroy infrastructure
- wash away crops and farmland - land left unusable
- threatens lives of people and animals
Other than bringing massive floods, why else can jökulhlaups be dangerous?
They also carry enormous boulders,huge blocks of ice and icebergs.
