Volcanoes Flashcards
(41 cards)
Shield Volcanoes
Basalt lavas are relatively silica-poor (45-50% SiO2) and as a result, are less viscous. This flowing lava forms broad, shield-shaped volcanoes with large diameters and low heights.
Lava will often erupt from vents or flanks of volcanoes. Each layer of rock will represent many hundreds of thin flows of basic lava.
Volcanic Domes
Consists of silica rich (70%) lave (usually rhyolite and andesite). These flow less readily, these lava’s pile up close to the vent and build high peaks. They are associated with violent eruptions, as the dome will block the vent and trap gas. The vent may also be filled with volcanic debris.
Stratovolcano
Composite volcanoes comprise alternating pyroclastic layers and lava flows. They can grow both domes and cinder cones with alternating slopes. They will have intermittent eruptions over a long-time span.
The lava is mostly gas-laden and andesitic.
The magma can accumulate in significant reservoirs over subduction zones.
Example of Shield Volcanoes
Hawaii (Mauna Loa, Kilauea, Mauna Kea) and Olympus Mons Shield Volcano on Mars
Example of Volcanic Dome Volcanoes
Mount St.Helens
Example of a Cinder-cone volcano
Paricutin volcano in Mexico, Cerro Negro in Nicaragua.
Examples of Strata Volcanoes
Mount Fuji and Mount Vesuvius
Cinder-cone Volcanoes
Formed entirely out of pyroclastic materials that accumulate near the volcanic vent. Pyroclastic activity is more viscous, silicic magmas, and falls symmetrically to form a cone shape.
They have steep sides, with fragments falling from the summit and smaller fragments falling from the base.
They are small with a short activity.
Caldera
Result when a violent eruption empties a volcano’s magma chamber, which then cannot support the overlying rock. It collapses, leaving a large, steep-walled basin.
Can be up to 50 km in diameter.
Resurgent Calderas
Calderas with continuing volcanic activity
Example of a resurgent caldera
Yellowstone and Crater lake in Oregon
Formation of Crater Lake in Oregon
- Fresh magma filled the magma chamber of Mount Mazama and triggers a volcanic reaction.
- The eruption continues and the magma chamber becomes partially depleted.
- The mountain summit collapses into the empty chamber, forming a caldera. Large pyroclastic flows accompany the collapse, blanketing the caldera, and a surrounding area of hundreds of square kilometers.
- A lake forms in the caldera. As the residual magma in the chamber cools, minor eruptive activity continues in the form of hot springs and gas emissions. A small volcanic cone forms in the caldera.
Pyroclastic Flows
- Mixtures of hot gases, ash, and rocks form a superheated gas and dense current.
- generated during violent volcanic eruptions where molten material cools before falling to earth
- different from central eruptions
Example of Pyroclastic flow
Mount Vesuvius in 79 AD in Pompeii
Phreatic Explosion in the Pacific
The result of excessive subsurface pressure due to steam buildup (similar to an exploding boiler). Volcanic islands are susceptible to seawater seepage, and when magma meets water it turns into superheated steam.
Example of a Phreatic explosion
island of Krakatoa in Indonesia
Fissure Eruptions
Highly fluid basaltic lava may flow out of fissures, rather than a single vent. The highly fluid basalt erupting from fissures forms widespread layers rather than mountains.
Large igneous province
Large fissure eruptions on land
The most geographically important fissure eruption is ___
occurring at the spreading centers of mid-ocean ridges. The majority of volcanic rock is produced from fissure eruptions.
Flood Basalts
Successive eruptions on flat surfaces produce plateaus characterized by layered flood basins.
Example of a large igneous province/ flood basin
Laki eruption in Iceland killing 1/5 of the population
Siberian Traps
Flood basalts cover an area twice the size of Alaska. They erupted 250 million ya and are implicated in a global mass extinction event.
Diatremes
Eruptions originating from the asthenosphere. They form by:
- Gas-charged magma from deep in the mantle forcing its way upward from the lithosphere
- Magma breaks off and carries crust and mantle fragments as it explodes
- After the eruption, the feeder channel forms a diatreme of solidified magma and rock fragments called breccia
- Softer sediments of cone and surface erode, leaving the diatreme core
Kimberlites
A form of diatreme and a volcanic form of peridotite (a rock made of mostly olivine). They contain many fragments, such as diamonds, and form in mines in South Africa and Canada.
