Test 1 Flashcards
(29 cards)
What is a hazard?
potential threat to humans and their welfare
What is a risk?
probability of loss (deaths, injuries, damage, etc.) as a result of the natural event
What is vulnerability?
Potential loss or degree of loss from the event
0 = no damage/no risk, 1 = total loss
What is a disaster?
a hazardous event affecting a community in an adverse way such that essential social structures and functions are disrupted
What is prediction and forecasting?
A statement that a particular natural hazard will occur:
- With a given probability
- During a specific timeframe
- In a specified geographic area
What is mitigation?
efforts to reduce or minimize the effects of a hazard in the future
What is the recurrence interval?
Average time interval between the occurrence of two events of given magnitude
- Ex: an earthquake of magnitude 5 happens once every 10 years, on average - corresponds to a 10% probability of occurrence
What is the difference between lava and pyroclasts?
Lava erupts quietly and pyroclasts are violent
What is a super volcano?
- When it erupts, it puts out a huge volume of magma
- Erupt very infrequently
- Forms a large crater (caldera)
What are the two controls of explosivity?
- Silica (SiO2) content of the magma
- Gas content of the magma
What’s the difference between basalt, andesite, and rhyolite?
- Basalt: 50% silica, gas-poor (not very violent)
- Andesite: 60% SiO2, gas-rich
- Rhyolite: 70% SiO2, gas-rich
What is a divergent boundary?
Spreading apart (mid-Atlantic ridge)
- The mantle rises and melts, producing magma
- Magma erupts mainly as basaltic lava flows
What is a subduction boundary?
One plate moves under the other (Pacific Ocean)
- The subducted oceanic plate heats as it plunges
- Volcanoes parallel the subduction zone
What are hot spots?
Located in the middle of a plate
- Magmas from deep within the mantle move up vertically
- Mantle plumes stationary relative to the drifting tectonic plates
What are cinder cones?
- Erupt only once during lifetime
- Explosive, but small in size
- A pile of pyroclastic debris at the angle of repose
- Basaltic gets fragmented, producing a cinder cone
- They can show explosive and lava activity at the same time
What are shield volcanoes?
- Broad, gently sloping volcanoes
- Mainly basaltic lava flows
What are stratovolcanoes?
- Alternating layers of lava and pyroclastics
- Mainly andesitic in composition
- Typical of subduction zones
- Can be extremely explosive and violent
What is a caldera?
A large depression generally caused by the removal of large quantities of magma from beneath a volcano, causing the ground to “collapse” into the emptied space
What are lava domes?
- They grow vertically because they’re made of very high contents of silica
- The magma is highly viscous- it can’t easily flow so it builds up vertically
What are lava flows?
- Basaltic lava flow
- Its low silica content and high temperature means it is quite fluid (but stickier than maple syrup)
What is pahoehoe lava?
- Hawaiian term for smooth, ropy lava
- Generally exhibits fluid-like textures
What is Aa lava?
- Blocky on the surface, and comparatively cool
- Below, lava is fairly massive and much hotter
What is fire fountaining?
- Sometimes, basaltic lava can contain lots of gas
- Small explosive eruptions form fire fountains, which coalesce to form a lava flow
What are flood basalts?
- The previous examples represent small-scale activity
- But basaltic eruptions can be huge, forming lava plateaus
- These huge outpourings may occur over several million years and contribute to mass extinctions
