VOLCANOES-CH. 13

Vocabulary Magma- liquid rock produced under Earth’s surface Volcanism- any activity that involves movement of magma to Earth’s surface Lava- magma that flows onto Earth’s surface Volcano- VENT or FISSURE in Earth’s surface through which magma and gases are expelled (ejected;erupted) Vent- opening in the Earth in which lava erupts MELTING POINT- The temperature at which rock will melt.

How does Magma form? The mantle is solid because of the large amount of pressure. This causes rock in the lower mantle to stay BELOW its melting point. All rock is composed of minerals. These minerals have a specific melting point.

3 ways magma can form The temperature of the rock rises above the melting point of the minerals in the rock, they will begin to melt. When enough pressure is removed from rock, the melting point of the minerals in the rock lower and the rock will melt (has the ability to melt at a lower temperature). (DIVERGENT BOUNDARIES) When fluid (such as water) is added, it also lowers the melting point of the minerals in the rock and cause the rock to melt. (SUBDUCTION ZONES).

VOLCANISM Magma rises up through crust because it is LESS DENSE than surrounding rock Bodies of magma get LARGER because 1) they melt rock around it adding to the magma, and 2) as magma rises through cracks it breaks off surrounding rock, some melts and is added to body of magma

Where are zones of volcanism found? Plate boundaries (convergent and divergent) SUBDUCTION ZONES: OCEANIC- CONTINENTAL- As oceanic plate subducts, a deep trench forms. Fluids combine with the crust and mantle and decrease the melting point (this means the rock will melt at a lower temperature);magma rises because less dense than crust and erupts onto earth’s surface forming a line of volcanic mountains OCEANIC-OCEANIC Same as above, but deep ocean trench forms. Line of volcanic Islands form, instead of mountains.

Marianas Trench httpvideo.nationalgeographic.com/video/news/deep-sea-challenge/cameron- how-deep://

Mid-Ocean Ridges Form a major zone of volcanic activity Pillow lava is a volcanic rock that forms here https://www.youtube.com/watch?v=hmMlspNoZMs Most underwater volcanoes are unnoticed by humans Exception: Iceland- Part of the Mid-ocean ridge above sea level; one half of Iceland is on the North American Plate moving westward and the Eurasian plate moving eastward.

Hot Spots

Pluton

ERUPTIONS There are 2 types of magma MAFIC- contains magnesium and iron/ dark in color FELSIC- rich in silica/ light in color Quiet- mafic w/ low viscosity. Eruptions from ocean volcanoes. Explosive- felsic lava of continental volcanoes.

PYROCLASTIC MATERIAL Classified according to size Less than 0.25 mm = volcanic dust Less than 2 mm = volcanic ash Less than 64 mm = lapilli (luh PIL ie) Large clots of lava that cool as ejected = volcanic bombs Solid rock blasted from the vent = volcanic blocks

TYPES OF VOLCANOES Lava and pyroclastic material build up around a vent to form a volcanic cone CRATER- the funnel shaped pit at the top of the cone.

SHIELD- formed from quiet eruptions; lava flows out; hardens; and builds up to form the cone. Broad base; gentle sloping sides

CINDER CONE- steep slopes; only a few meters high; made from build up of pyroclastic material.

COMPOSITE made of alternating layers of hardened lava flows and pyroclastic material; largest volcanic mountains.

CALDERA