Page 2 - 2009 DT 7 issues

Slumbering Giants The majority of the world’s volcanoes not always be explosive, but they can
are located at plate margins, whether produce prodigious amounts of lava.
n the morning of May 18, continental or oceanic. Mauna Loa is such a volcano, rising
1980 in the state of Washing- Although Mt. St. Helens’ eruptions 4 km above sea level. Composite or
Oton, Mt. St Helens awakened are more frequent than most other stratovolcanoes, such as Mt. Vesuvius
from a 20-year slumber. The volcano Cascade volcanoes, neighboring and Mt. Etna, combine explosions of
erupted with an explosion that tore out Mt. Rainier is categorized by the U. rock particles with alternating lava
the north face of the mountain, roaring S. Geological Service as the most flows. They form calderas, or funnel-
upward and outward, spewing tons of dangerous volcano in the Cascades shaped pits, at their summit.
ash into the sky. Massive rock and ice due to the risk of catastrophic debris Alaska fields many candidates
debris blasted into Spirit Lake, bar- flows of rock and ice on to the growing for potential eruption. Currently Mt.
reling over a ridge 1,300 ft high. The population surrounding it. Its latest Redoubt, along the Cook Inlet, is
millions of tons of mountain side cas- eruption in the 1840s, along with at “Yellow Alert” status and bears
caded 14 miles down the Toutle River, evidence of large eruptions 1,000 and watching. But the largest and most
propelled by pressurized gasses within 2,300 years ago, caused its glaciers to active volcanoes in the U.S. are on
the volcano that ultimately devastated melt, producing thick concrete-like the island of Hawaii. Kilauea, on
nearly 230 square miles of forest. Nine debris flows, or lahars, that swept down the Big Island, may be the Earth’s
hours later the mountain settled back all of its river valleys. most active and is currently the most
into a fitful sleep, but not before it had Eruptions are not all violent. dangerous. As of December 7, 2008, it
claimed the lives of 57 people. Occasionally lava (magma so called, was at category “Orange” on the Alert
It wasn’t over yet. The mountain once it breaks
continued to erupt violently, then forth from the
more quietly, until 1986. On October interior) may
1, 2004, it came to life once more. A flow through
spume of steam and ash rose 10,000 vents in the side
feet into the air. A few weeks later, hot of a mountain,
lava oozed out of the crater, building a never building
up a dome or
small mountain in a matter of days. p r o d u c i n g a
Mt. St. Helens is ranked number
two on the list of the 18 most dangerous blow out. There
are a number
U.S. volcanoes. It is only one of at of ways that
least 20 volcanoes rated as “active” volcanoes form
that stretch like a string of pearls and eventually
from British Columbia to California. erupt. For this
Numerous volcanoes populate the reason, terrestrial Mt. St. Helens, Washington State
continental margin, from Alaska volcanoes are broken into types:
through Baja California and Mexico. Cinder cones are formed by Scale, with an eruption “likely at any
As oceanic plates dive under the an explosion of rock particles and time.” Its sister volcano, Mauna Loa,
continents, they are heated to the generate little or no lava. Mt. Fuji in rising 56,000 feet from the sea floor
melting point, releasing magma (liquid Japan is an example. Shield volcanoes, is, the largest volcano on the planet
rock) which works its way up through such as Mt. St. Helens, are usually and one of the most active in the
fissures in the rock, melting more rock massive and are formed through world, having erupted 33 times since
as it goes. If a magma chamber forms, successive, quiet eruptions that build 1843 alone. The volcano’s earliest
continuing pressure may push the up over time into a gently sloping eruption is estimated to have occurred
molten rock to the point of an eruption. dome-shaped mountain. They may at least 700,000 to 1,000,000 years
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