<ul><li>Magma – Molten rock beneath the surface. </li></ul><ul><li>( Mafic – dark ocean crust & Felsic – Light continental crust.) </li></ul><ul><li>Lava – Molten rock on the surface. </li></ul><ul><li>Volcanism – The movement of magma to the earth’s surface. </li></ul><ul><li>Volcano – The vent on the earth’s surface through which gases and magma are released. </li></ul>
<ul><li>Subduction Zones </li></ul><ul><li>When one tectonic plate moves under another. </li></ul><ul><li>Mid-Ocean Ridges </li></ul><ul><li>The largest amount of magma comes to the surface where plates come apart at mid-ocean ridges. </li></ul><ul><li>Hot Spots </li></ul><ul><li>Volcanically active area of Earth’s surface, commonly far from a plate boundary. </li></ul>Volcanic Zones
Most Volcanoes are found along Subduction Zones
At 8:32 Sunday morning, May 18, 1980, Mount St. Helens erupted. Shaken by an earthquake measuring 5.1 on the Richter scale, the north face of this tall symmetrical mountain collapsed in a massive rock debris avalanche. Nearly 230 square miles of forest was blown down or buried beneath volcanic deposits. At the same time a mushroom-shaped column of ash rose thousands of feet skyward and drifted downwind, turning day into night as dark, gray ash fell over eastern Washington and beyond. The eruption lasted 9 hours, but Mount St. Helens and the surrounding landscape were dramatically changed within moments. In 1982, the President and Congress created the 110,000-acre National Volcanic Monument for research, recreation, and education. Inside the Monument, the environment is left to respond naturally to the disturbance.
Mount St. Helens Blows Smoke on October 1st After Eighteen Years Rest For days the mountain rumbled. And then today, on Friday, October 1st, 2004 at approximately 12:04 Pacific Daylight Time (3 pm EDT) and at 15:14 (6 pm EDT), Washington's Mount St. Helens erupted steam and ash after an eighteen year slumber. The 8,364-foot volcano is located in Kelso, Washington about 30 miles south of Seattle. It is part of a volcanic "ring of fire" so vast that it encircles the Pacific Ocean.