ISDN essays

ISDN essays Gas bubbles form in magma. As magma rises higher and higher, the bubbles get bigger and bigger. When the magma reaches the surface and erupts, the bubbles expand very rapidly, and an explosive eruption happens. The easiest answer is that it erupts when the pressure of the magma inside becomes so great that the volcano splits and the magma gets out. The magma pressure can get high if the supply to the volcano from the Earth's mantle is high. The magma pressure can also get high if magma is just sitting around in the magma chamber within the volcano. This is because as the magma in the chamber starts to cool off, it releases gases. These gases can increase the pressure until the volcano fractures and you have an eruption. Mount St. Helens National Volcanic Monument 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. In a few moments this slab of rock and ice slammed into Spirit Lake, crossed a ridge 1,300 feet high, and roared 14 miles down the Toutle River. The avalanche rapidly released pressurized gases within the volcano. A tremendous lateral explosion ripped through the avalanche and developed into a turbulent, stone-filled wind that swept over ridges and toppled trees. Nearly 150 square miles of forest was blown over or left dead and standing. 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. Wet, cement-like slurries of rock and mud scoured all sides of the volcano. The eruption lasted 9 hours, but Mount St. Helens and the surrounding landscape were dramatically changed within moments. ...