Earth Science: Volcanic Eruptions
When the huge pressure that builds beneath a volcano prior to an eruption is finally released, the results can be spectacular. Ash and pyroclastic material may tower 12.5 miles (20 km) into the sky, while molten lava pours down the mountainside.
Volcanoes eject the products of their eruptions as gases, liquids, and solids. Effusive eruptions produce basic lava flows, which are less viscous and often flood large areas before solidifying. These eruptions can last for centuries and have historically had devastating effects on Earth’s climate, releasing large quantities of greenhouse gases, steam, and carbon dioxide into the atmosphere. Eruptions of viscous lava (which explodes during degasification) mingle lava with rocks.
These explosive eruptions, called pyroclastic emissions, bombard the regions that surround them, rapidly burying the nearby countryside under several feet of ash. The finest pyroclastic materials can collect and form a pyroclastic cloud with a temperature of about 1800°F (1000°C) and speed up to 620 miles per hour (1,000 km/h). Explosive eruptions are usually accompanied by heavy rainfall as airborne ash causes steam to condense from the air around the eruption site.
When rainwater combines with volcanic ash, large sheets of potentially destructive mud and debris, called lahars, begin to flow down the volcano’s slopes to the land below.
Lava
Volcanic lava may manifest itself in many forms, according to the conditions accompanying volcanic eruptions and subsequent patterns of lava cooling. Thin smooth-flowing magma forms “pahoehoe lava,” which has a smooth, billowy, undulating surface. Viscous “aa-lava,” however, solidifies in sharpe-dged blocks.
Acidic lava that froths during degasification forms pumice, but abrupt cooling creates noncrystalline or glassy vitreous rocks, including obsidian. When lava comes into contact with water, pillow lava is formed, in rock masses that can range up to three feet (0.9 m) in diameter.
BEGINNING ANEW
Thousands of square miles of land can be destroyed by a volcano’s eruption. and it can seem impossible that environments turned into such wastelands could ever recover
Yet only months alter the 1980 eruption only Mount St Helens In Washington state, the first plant growth reappeared on the nutrient rich ash fields surrounding the mountain Animals returned to the area soon afterward, however, the local ecosystem may need 200 years to return to its pre eruptive state