volcanology: is the study of volcanoes. many good things come from volcanoes. fertile soil, new land, recycles minerals, gave us atmosphere, recreation

rocks relatively rich in iron and magnesium are sometimes referred to as mafic

relatively silica rich rocks tend to be rich in feld spar as well such rocks are therefore sometimes called felsic

basalt: "ultra mafic" material rich in iron and magnesium that tends to form at rifts on the sea floor. forms thin lava

rhyolite: silica rich material formed by the melting of the earth's crust as magma rises.

forms thick lava

andesite: material with silica in a relatively indeterminate from because of silica content between basalt and rhyolite: forms medium lava

fissure eruption (or lava curtain): the eruption of magma out of a crack in the lithosphere.

Fountain: a lava eruption from a small hole.

shield volcano: formed from quiet eruptions high in basalt content. flat wide shield like volcano with a large surface area typically formed be thin lava flows,

Pahoyhoy: smooth basalt (relatively low in silicate) lava formation that forms smooth rocks.

Aa lava: forms from rhyloite or andesite lave with high silica content rough jagged rocks that are painful to the feet after they harden.

lava rifting: lava that has crusted and then breaks

pillow lava: forms on the sea floor. the outer lava cools faster and forms a tube that is constantly cracking as the lava moves

obsidian: black volcanic glass

the circum pacific "the ring of fire" is the most active volcanic region and is caused by subduction zones.

lava is about 2400 deg F and is fairly well insulated

volcanic dome: compact steep sided structure resulting from thick lava flows, sometimes explodes.

pyroclastics: pieces of violently erupted volcanic matter, harden and shape in the air and are often called bombs

cinder cone: when pyroclastics are thrown close to the earth, they tend to land and form a symmetrical cone over time around the opening of the volcano.

stratovolcanoes: volcanoes that build up over time from both smooth lava flows and pyroclastic explosions.

composite volcanoes: another name for strato volcanoes

lahar: volcanic mud flow created by the combination of ash and water.

pyroclastic flow: a deadly, denser than air mixture of hot gases and fine ash, also called a nuee ardente or glowing cloud can reach temps of over 1000 C

phreatic eruption: caused when large quantities of sea water seep down to the magma and build up steam pressure like an exploding boiler.

active: rough term, a volcano is generally considered active if it has erupted in recent history. and is not too eroded by time

dormant: inactive for the present, but present the possibility of becoming active again.

extinct: a volcano with no eruptive history lots of time erosion and no signs of becoming active

caldera: the rim of the crater enlarged crater on the summit of a volcano formed either by the collapse of a magma chamber or the explosion of the summit.

volcanoes are easily eroded most visible today are very young. older ones are no longer visibly recognizable as volcanoes.. rather just mountains.

Volcanic Hazards:

lava flows

Pyrclastics---bombs, hardened lava

Lahars-- mud slides

Nuee' Ardente: clouds of burning ash, and gas

toxic gas

steam explosions

acid emissions: (H2 SO4 )acid rain

Tusunamis

ash falls

Volcainc Benefits:

new land

adds needed water and gases to the atmosphere

new mineral deposits

geothermal energy

refertalize soil

recreation