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explosive eruptions of new volcanic material-extremely hazardous.
average lifetime: 900,00-1,000,000 years
Flank and Summit eruptions are common
form at subduction zones
concave upward
occur on landward side of subduction zones
they are stratified |
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More voluminous then strato
concave downward |
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Moderately explosive eruptions of new volcanic material
average lifetime= 1-100 years
frequently form on flanks & summits of larger stratovolcanoes
steep conical hills of volcanic fragments that accumulate around and downward of the vent |
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Tephra, ejected material of all sizes
solid by the time it hits the ground
most numerous type volcano
rarely reactivated |
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similar to cinder cones except that some of the material is still molten when it reaches the ground
relative to cinder cones, are smaller and have a shorter lifetime |
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Effusive eruption of new volcanic materials
average lifetime:1-100 years
Usually form after the explosive eruption of gas-rich magma at stratovolcanoes
Rounded steep sided mounds of lava formed near the volcanic vent by very viscous magma
one or more individual lava flow |
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Large, circular, steep walled depression at the summit of a volcano
up to 10 km in diameter
walls up to 100 m high |
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| smaller, circular depressions formed by the explosive evacuation of rock during eruptions |
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Explosive disintegration of the top of a volcano
collapse of the top of a volcano into empty underground magma chamber |
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Volcanoes of mixed origin, stratovolcano with lava domes
overlapping stratovolcanoes with multiple summits
Due to changes in eruption habit, location of principle vent area |
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A wide, low, relief crater formed by shallow explosive eruptions
Generally no new volcanic material erupted
Groundwater is heated and boils causing steam explosions
Often filled with water to form lakes |
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Explosive eruptions of new volcanic material and excavated country rock
Triggered by interaction of water and rising magma
Built of multiple pyroclastic surges that build ring of debris around explosion crater |
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| a large depression created by the collapse of a volcano |
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| A simple volcano built from blobs of lava ejected from a single vent |
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| Built from countless outpourings of fluid lava flows |
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| built of layers of lava, ash, and volcanic debris |
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| mound formed when viscous lava pulls up around vent |
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can be located anywhere at tectonic plate boundaries or in the center plates
in continental or oceanic crust |
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Mantle plumes rise from deep within the mantle, possibly the core-mantle boundary
rise via convection
when reaches base of lithosphere, plume head spreads out, potentially feeding multiple volcanoes simultaneously |
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plumes are stationary for millions of years, provide a continuous source of magma.
As the tectonic plate moves over stationary mantle plumes, a line of volcanoes is formed, only volcanoes immediately over plumes are active |
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| Formation of Hot Spot tracks |
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typically produce shield volcanoes
the largest volcanoes are immediately above the hot spot
once the supply of lava is turned off the island moves away from the hot spot, the volcano gets smaller |
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| Hot spot occurrences under oceanic crust |
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| a coral island that encloses a lagoon and is surrounded by open sea |
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| Volcano and reefs sink below sea level |
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Since formation completely isolated from mainland
plants and animals only reached island by chance
allowed many unique plants and animals to form
composed primarily of large shield volcanoes |
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| Islands composed primarily of stratovolcanoes |
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Combination of hot spots and divergent plate boundary
as tectonic plates move about surface of earth, oceanic spreading center coincidentally moves over a hot spot
double dose of volcanism created the topographic high |
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Best place to harness geothermal energy
Geothermal plants provide reliable power for 60 million people in the world
Iceland is almost run entirely on geothermal energy |
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thought to be a continental hot spot track
flat area lacking topography, resurfaced by erupted lava
oldest part of plain in vicinity of columbia river flood basalts |
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Combination of a hot spot and divergent plate boundary, progression from hot spot to oceanic spreading center
hot spots may play a critical role in military continental break up. |
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high efficiency and low cost
lower co2 emissions than fossil fuels |
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Definition
| Advantages of geothermal energy |
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scarcity of suitable sites
depleted if used to rapidly
moderate to high local air pollution
noise and odor
cost too high except at the most concentrated and accessible source |
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| Disadvantages of geothermal energy |
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covered with loose sediment and lava flows
deep cracks run parallel to the rift valley
normal faults parallel rift valley and create steep valley walls |
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Effusive submarine eruptions
20 eruptions/ year worldwide
none have been directly witnessed |
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| how the mid ocean ridge system works |
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Creservoirs of molten lava, exists 1-3 km below ridge axis
height and width: a few km's
segmented
only the uppermost portion of chamber fully melted |
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Magma rises from magma chambers to shallow depth
Rising Magma temporarily fills in cracks between spreading plates
additional lava erupts onto ocean floor to form pillow basalts |
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Lava squeezes out like toothpaste through the thin skin of the flow
The surface of the exposed lava quickly solidifies, forming a pillow like structure |
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| Hydrothermal circulation of ocean water |
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seawater drawn into oceanic crust along the sides of rift
As water approaches underlying magma chamber, it is heated
heated water dissolves various metals and other elements
hot water rises and is ejected at submarine hot springs |
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Dissolved metals come out of solution making water look black
Bacteria derive energy from chemosynthesis(energy from chemical reactions) as opposed photosynthesis
supports incredible and diverse ecosystem with well developed food web |
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Effusive Eruption: Lava Flows
Explosive Eruptions: Pyroclastic flows, lahars, ash fall, ash clouds, phreatic eruptions
All eruptions/volcanoes: volcanic gas, landslides, tsunami |
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rapidly flowing mixture of rock debris and water
can travel 10's of km typically down river valleys
hot or cold
especially common at stratovolcanoes |
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without eruption: landslides mixed with water
During eruptions: melting of snow and ice by pyroclastic flows, lava flows
After eruptions:heavy rainfall, erodes deposited ash, sudden release of water from crater lakes |
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Definition
| How lahars are generated? |
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destroy by direct impact, often contain larger boulders and trunks
bury buildings, communities and valuable land in cement like layers of rock debris
May trap people
block tributary streams creating lakes that may suddenly flood |
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