Volcanoesand Plate Tectonics

 Most rock in the earth (except in the outer core) is solid because temperature is offset by pressure. Where the pressure is less than normal, or where excess water is in the rock, the rock will melt. Why? The rock particles are allowed to move more quickly.

 Liquid rock formed deep inside the earth  Most magma forms at plate boundaries where one plate is subducted under another, or at mid-ocean ridges.

 Any activity that includes the movement of magma toward or onto the surface of the earth

 For volcanism to occur, the magma must collect into a pocket and the magma must move upward through the crust. The liquid magma is less dense than the surrounding solid rock, so it slowly rises.

 Magma which breaks through to the surface of the Earth

Kilauea Volcano

 The vent and the volcanic material that builds up on the earth’s surface around the vent

 The opening through which molten rock flows onto the surface

 Subduction Zones  Mid-Ocean Ridges  Hot Spots

 Region where one lithospheric plate moves under another. This is oceanic to continental, where a trench is formed off the coast and volcanoes are formed at the edge of the continent, like here in Washington.

 Forms a trench and an associated island arc, a string of volcanic islands that can grow into larger chains, like Japan

 System of undersea mountain ranges that wind around the earth. Magma rises to the surface along long, narrow cracks called rifts.

 The middle of Iceland is the surface of the Mid-Atlantic Ridge. Here large fissures, or cracks through which lava flows, are found.

 Heat build-up beneath large, old continental interiors— suggests long-term  Instability of super continents; however ultimate causes of rifting not well understood. Several possibilities  1. plume-related uplift, stretching and rifting tendency for rifts to start at a point  2. gravitational collapse of mountain belts  3. build-up of heat beneath a large continental interior (whereas heat is easier to distribute under ocean lithosphere owing to spreading centers  4. propagation of rifts from the edge of a continent into the interior “welding” onto a plate with different sense of motion this implies reactivation of old rifts or zones of weakness

 Rifts develop at 120° to each other  Partly as stretching and crustal thinning, partly as transform motion between adjacent parts of a continental block  One rift arm usually fails to develop fully; perhaps because motion is ‘stolen’ by other rifts— forms an “aulacogen”

 Area of volcanism within a lithospheric plate

 The hot spot remains stationary but the lithospheric plate moves slowly. Thus the volcano on the surface is eventually carried away.

 Volcanic activity ceases for that volcano and a new volcano forms over the hot spot. The islands are eroded away and sink beneath the waves to form a seamount chain.

High volcanic island Transitional island Low corral Atoll

 Also a hot spot.

Elevation 14,410 feet

 After May 18, 1980  Before

 Evidence gathered by human exploration and spacecraft indicate that many planets and moons show evidence of volcanism.

 Most are not currently active, but Io, a moon of Jupiter, has more volcanic activity than the earth.

No evidence of plate tectonics.

 The dark areas of the moon (the maria) are covered with basaltic lava flows.

 The heat needed to create the magma could have come from a long period of meteorite bombardmen t.

 Some have smooth, lava- flow interiors and gently sloping, channeled exteriors.

 Most of the craters on the moon are the result of meteorite bombardme nt

 Current thought is that the maria are volcanic in origin, while the craters are from meteorite impacts.

 No evidence of plate tectonics on Mars, but there are many volcanoes and volcanic features on the Martian surface.

 Largest volcano in the solar system. So tall (28 km) that the summit reaches the upper parts of the atmosphere.

 The base is 600 km across, and its caldera, 70 km across. Made up of basaltic lavas and has gently sloping sides. So what kind of volcano is it? Shield volcano

 Had to have been active for millions of years above a hot spot, continuously building up layers of lava.

 About the size of the earth’s moon, it is probably the most volcanically active body in the solar system.

 First photographe d in 1979.

 Several thousand tons of material erupted each second.

 The color of the surface is a bright yellow-red and black.

 Powerful volcanic plumes, as many as 9 eruptions seen at the same time.

 The lavas on Io are neither mafic or felsic, but of sulfur-bearing compounds.

 The yellowish and red colors of the surface indicate the volcanic material is primarily sulfur and sulfur dioxide.

 Jupiter has both intense magnetic and gravitational fields.

 This moves the surface of Io and heats the interior, which leads to volcanism.

Martian volcanoes – Tharsis Ridge