| Bear Viewing Association To watch, to wonder, and to conserve [email protected] Ph/Fax (907) 260-9059 (Office) 39200 Alma Ave. Soldotna, AK 99669 |
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Alaska's Mt. Redoubt, like Washington's Mt. St. Helens, is now just fuming -- venting steam laced with various acids and other toxic chemicals.
St Helens
| The 1980 eruption of St. Helens and the 1990 eruption of Redoubt spewed out toxic chemicals and ash. Although the ash is glowing red hot when first ejected, it quickly cools enough to turning grey, but can still be over 1000 degrees F. The red color of the ash from Redoubt's eruption, shown on the previous page, comes from the setting sun |
Redoubt
St Helens
Most of the steam vented from Mt. Redoubt originates as snowmelt and rainfall on the surface, which percolates down through the porous volcanic
ash and cinders, which have been welded together by their own heat and weight, into a kind of rock that forms most of the cone. Even where sinking
water encounters a layer of solidified lava, it can often pass through cracks in the lava. Heat from magma turns the water into steam, causing it to
expand, further cracking the rock, allowing even more water to percolate downward and form even more steam. This process may begin slowly, but
once the country rock is cracked enough to release pressure on the deep magma, steam generation escalates exponentially, something like the
way carbon dixoide causes champagne to explode out of a bottle when the cork is removed (steam bubbles indicated by circles in the diagram
above right. The conversion to steam can occur so rapidly, in such great volume, that it explodes the rock into particles, some less that 0.1 inch
(0.2 cm) in diameter -- i.e., to the size of the ash left in a fireplace after burning wood.
ash and cinders, which have been welded together by their own heat and weight, into a kind of rock that forms most of the cone. Even where sinking
water encounters a layer of solidified lava, it can often pass through cracks in the lava. Heat from magma turns the water into steam, causing it to
expand, further cracking the rock, allowing even more water to percolate downward and form even more steam. This process may begin slowly, but
once the country rock is cracked enough to release pressure on the deep magma, steam generation escalates exponentially, something like the
way carbon dixoide causes champagne to explode out of a bottle when the cork is removed (steam bubbles indicated by circles in the diagram
above right. The conversion to steam can occur so rapidly, in such great volume, that it explodes the rock into particles, some less that 0.1 inch
(0.2 cm) in diameter -- i.e., to the size of the ash left in a fireplace after burning wood.
Magma is created, of course, because of plate tectonics, where the plate forming the bed of the Pacific Ocean is forced under the surrounding
continents. the deeper the plate margin is drive down toward the core of the Earth, the more it melts. The molten rock, known as magma, melts its
way upward through the overlying solid rock, eventually reaching the surface and erupting. The diagrams below show the various plates (left) and
the hundreds of volcanoes (red dots on map at right) that form the Pacific Ring of Fire.
continents. the deeper the plate margin is drive down toward the core of the Earth, the more it melts. The molten rock, known as magma, melts its
way upward through the overlying solid rock, eventually reaching the surface and erupting. The diagrams below show the various plates (left) and
the hundreds of volcanoes (red dots on map at right) that form the Pacific Ring of Fire.
Pacific Plate
| Pacific Ring of Fire (each red dot is a volcano) |
If a volcano's magma is low in silica, but high in water (e.g., in Hawaii), it doesn't explode into particles, but fountains out as liquid rock, then
flows down the slope of the volcano and beyond, even down slight slopes, incinerating and crushing everything in its bath. Mt. Redoubt instead
sent out an avalanche of rock fragments, ash and superheated steam avalanching downhill at over 200 mph-- a so called pyroclastic flow. As
glacial ice melted, this steam and water joined the rock fragments, avalanching downward at over 100 mph. The photos below are of lava.
flows down the slope of the volcano and beyond, even down slight slopes, incinerating and crushing everything in its bath. Mt. Redoubt instead
sent out an avalanche of rock fragments, ash and superheated steam avalanching downhill at over 200 mph-- a so called pyroclastic flow. As
glacial ice melted, this steam and water joined the rock fragments, avalanching downward at over 100 mph. The photos below are of lava.
Redoubt