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Dust and Ash
On May 18, 1980, Mount St. Helens erupted after lying dormant for 123 years. The huge explosion was heard 200 miles away in Vancouver, Canada. The eruption destroyed the mountain's north side, shortened the mountain by 1,300 feet and sent an avalanche of rock tumbling down the mountainside. A cloud of dust was blasted 12 miles into the air as flows of hot gas and ash incinerated everything they touched. The eruption flattened every tree for 15 miles; blanketed the surrounding landscape with dust; and left rivers choked with mud, broken trees and ash.
Lava Flow
Beneath Earth's surface are pockets of molten rock called magma. Volcanic eruptions release this molten rock as lava. Lava slowly flows across the landscape, burying roads, burning forests and destroying buildings. However, the lava eventually cools, forming new rocks and building up Earth's crust and forming new landforms such as the Hawaiian Islands. After decades or centuries, life returns to the area. Nutrients in the ash promote the growth of lichens, moss, flowers and trees. The plants break down the rocks into rich soil. Some of the richest farmland in the world is near volcanoes.
Volcanic Gases
Volcanic eruptions send gases into the air such as carbon dioxide, hydrogen fluoride and sulfur dioxide. These gases can have mixed results. For example, sulfur dioxide causes cooling by forming aerosols that reflect sunlight. Fluorine gas condenses into rain or mixes with ash. Animals that eat grass tainted by fluorine can develop fluorisis, which destroys their bones and kills them. In August 1986, after an eruption at Lake Nyos in Cameroon, Central Africa, 1,700 people died from carbon dioxide poisoning. Carbon dioxide is also a greenhouse gas that traps heat and contributes to global warming. However, volcanoes only generate about 110 million tons of carbon dioxide a year.
Atmospheric Effects
In June 1991, Mt. Pinatubo in the Philippines erupted after sitting quietly for 600 years. It created huge clouds of ash that blocked the sun for days and torrential rains that drowned several areas in mud. Eruptions like Mt. Pinatubo can affect the atmosphere in many ways. Rain occurs as steam released during the eruption reaches the atmosphere and condenses into clouds. Dust in the air can scatter sunlight, creating eerily beautiful red sunrises and sunsets. This same dust can spread around the globe, blocking sunlight and lowering temperatures. Enough particles can potentially cause global cooling, ice ages and mass extinctions.