types of volcanoes and hazards II Flashcards
the order basaltic, andesitic and rhyolitic shows increases is?
silica, viscosity, explosivity
what makes a volcano volatile?
water, various gasses
what are the properties of mafic lava (basalt)?
- low silica = low viscosity (runny)
- gases in magma can easily escape
- less explosive, lava flow dominates (add water, all bets off)
- mafic eruptions most common where magma has the most direct route to surface
- does not produce as much tephra or ash into the air
- lava is spouting !
what are the largest mountains on earth?
shield volcanoes
how are shield volcanoes made?
- basalt flows are fluid and build up one layer upon another layer over time
- may come out from flank eruptions
what are some properties of shield volcanoes?
- low topography
- predominantly build from mafic flows, but can have higher silica eruptions
what are the properties of cinder cone volcanoes?
- smaller than shield volcanoes
- formed by basaltic mafic lava that is very gas charged and rises very quickly
what are fissure eruptions?
- mafic lava not erupted through a central vent / hole
- cracks that open in the earth and lava fountains out of the cracks
- mid-ocean ridges is where the new crust is formed
- largest eruptions in earth’s history (flood basalts)
- can be extremely large and very intense
what are kimberlite eruptions?
- ultramafic
- large gas filled eruption that travels from mantle to surface in a very short period of time (rips a hole in the earth called mars)
what are the properties of felsic or intermediate lava?
- high silica = high viscosity (very thick)
- magma gasses cannot easily escape
- can produce very large eruptions
- large amounts of tephra and gas
where do stratovolcanoes / composite volcanoes form?
along subduction zones
what are some properties of stratovolcanoes?
- white vapor: water
- rock fragments and tephra is grey
- often snow on top of these mountains, meaning lava is immediately interacting with water, which generates large explosions
- produced by alternating layers of lava, tephra, and pyroclastic flow deposits
- classic cone volcanoes !!
- usually eruptions intermediate magma
- major eruptions can destroy
how do lava domes form?
- erupting lava is too thick to flow, causing it to pile up and rebuild stratovolcanoes
- lava reaches surface, very viscous, does not flow easily, pushes up, outside breaks and gets pushed around until whole crater is filled with lava domes, and then could potentially go back to forming a beautiful cone
how can lava domes collapse?
pyroclastic flows
what are calderas?
very large craters or gigantic depressions in the ground; can be very large
how are calderas formed?
- by a collapse
- earlier eruptions, big event, drain upper part of magma chamber, ground collapsed, steam explosions, filled by a lake
- formed by very large eruptions
what are the seven volcanic hazards?
- lava flows
- tephra (ash) fall
- pyroclastic flows
- mudflows
- tsunamis / landslides
- gas emissions
- climate change
what are lava flows?
large flows limited to fluid magma (ex. basalt), but there can be exceptions
what are some characteristics of lava flows?
- slower moving
- virtually impossible to stop
what is tephra?
- ash
- significant ash fall is generally limited to explosive eruptions (ex. felsic)
what are some consequences of tephra?
- hazard to planes (can’t see)
- respiratory illness
- mass loading (too much weight from debris, rock is heavy)
- short-term climate effects
- tiny bits of glass ejected and lithic fragments
what are pyroclastic flows?
fluid masses of rock fragments and gases that move rapidly in response to gravity (“flowing fire”
what are some characteristics of pyroclastic flows?
- most common in explosive eruptions or lava dome collapses
- very fast, hot and dense ash flows
what is a mudflow / lahar?
- debris flow composed of a slurry of pyroclastic material, rock debris and water
what are some characteristics of mudflows?
- incredibly dangerous
- needs a water source (typically it is snow)
- far reaching
- concrete consistency
- hot!
- can get warm, melt glacier and snow, volcanic rock weak, can cause a flow
what is a tsunami / landslide?
after volcano erupts or magma makes it to the surface and heats up the rock, displaced water and shock waves can cause a tsunami, and the heat can cause landslides
what is an example of tsunami / landslide?
hunga tonga - hunga ha’apai
what gasses make up volcanic emissions?
chlorine / hydrochloric acid
carbon dioxide
water vapor
fluoride / hydrofluoric acid
sulfur
what are the three time scales that volcanoes can impact on the climate?
- short-term cooling (large explosive eruptions)
- long-term (effusive eruptions like flood basalts)
- CO2 levels in the atmosphere (snowball earth)
