Volcanism Flashcards
What is a volcano?
A vent or fissure in the earth’s crust (or in the surface of some other planet) through which molten lava and gases erupt
Where does volcanic activity occur?
In 3 main areas of plates:
- Spreading ridges undersea and on continents (Divergent boundaries, new crust produced)
- Subduction zones (Convergent boundaries, old crust destroyed)
- Hot Spots within plates
Give an example of spreading ridge volcanism?
East African Rift Valley—a 6000 mi. crack in the earth dividing Asia and African plates and where new crust (magma) comes to the surface
Does volcanism happen in happen in the oceans?
Yes, Beneath the oceans a global system of mid-ocean ridges produces an estimated 75% of the annual output of magma.
Where does ubduction zone svolcanism occur in subduction zones?
Subduction zone volcanism occurs at convergent plate boundaries….where old crust is subducted in TRENCHES
Where are the trenches in the world and what are their names?
Slide 10
What is an example of subduction volcanoes?
Japan is a major subduction zone where 3 plates converge, and has 2 active volcanoes and lots of earthquakes
What happens when oceanic plates converge?
Island Arc Volcanoes may form
Give two examples of Island Arc Volcanoes?
- The Aleutian Island Arc—2 oceanic plates (N. Am & Pacific/Juan de Fuca) colliding
- Lesser Antilles Island Arc—Caribbean vs. Atlantic plate; 2 oceanic plates
What are hot spot volcanoes?
the plate is moving over the top of a “more or less” stationary hot spot
What percent of the worlds geysers are in yellowstone?
75%
What is yellowstone considered to be?
It is considered to be one of the largest supervolcanoes in the world with a giant caldera (crater-like feature) about 53 x 28 miles
How many volcanic eruptions have been in yellowstone?
3 major eruptions in cycle of about every 600,000 yeras
What is pyroclastic flow?
Pyroclastic flow is a ground-hugging avalanche of hot ash, pumice, rocks, and volcanic gases that rushes downslope at speeds of 75 mph or more—one of the most dangerous hazards!A Pyroclastic flowburns, shatters, buries, carries away, and/or poisons (gases) everything in its path
What are the four prominent landforms associated with volcanism
- Lahars (also a hazard)
- Lava flows (also a hazard)
- Volcanic peaks and Calderas
- Volcanic necks
What is lahars and how is it formed?
Pyroclastic flows melt snow and ice to form Lahars: Fast-moving slurry of rock, mud, ash, water that looks and acts like wet concrete; rush downslope stripping vegetation and soil.
How can lahars cause lakes to form?
by damming rivers
What is a type of lava flow?
Extensive Flood Basalt Plains (within plate) are another type of lava flow
What is flood basalt?
Lava flows abundantly from long fissures
What are the four types of volcanic cones? What are their sizes and shapes?
Stratovolcano, Caldera, Cinder Cone, Shield Volcano. Look at slide 47
What is a composite cone (stratovolcano)? What are they associated with?
A steep cone built by lava flows layered with pyroclastic flows—dangerous and explosive! They are associated with subduction zones
What are some active compositive/stratovolcanoes?
Mt. Etna, Mt. Vesuvius
What is a caldera?
Caldera (bigger than a crater):a basin-shaped volcanic depression at least 1 mi in diameter, caused by huge explosion and ground collapse
Where can calderas be formed?
In all kinds of volcanoes (e.g. mount saint helens, crater lake)
What are cinder cones?
Cinder Coneis asteep conical hill of loose rock fragments (cinder) that accumulate around a vent (crater), NO lava flow
Where can cinder cones be formed?
Can develop on any volcano
What are shield volcanoes?
These are the largest cone type. It is formed by layers of quiet lava flows associated with HOT SPOTS and spreading ridges (divergent boundaries)
KEY POINT: More predictable and Less Dangerous than composite / stratovolcanos –usually no pyroclastic flow
Where are shield volcanoes found?
divergent boundaries, hot spots
Where are composite (stratovolcano) found?
convergent boundaries
What is a volcanic neck?
Cooled hardened magma in “throat”of an old volcano that has since eroded away; the neck is very resistant to weathering and erosion
What are the benefits of volcanism to people?
Volcanoes provide fertile soils for agriculture, especially in tropics where soils suck. Humans can also harness volcanism for energy
