Volcanoes and Climate

Volcanoes can have a very dramatic effect on the climate. First, we'll talk about how volcanoes affect climate in the short-term, influencing the atmosphere, hydrosphere, and biosphere of the Earth. The immediate results can be devastating.

In the U.S. one of the most recent examples was the St. Helens eruption. The catastrophic eruption on May 18, 1980, was preceded by 2 months of intense activity that included more than 10,000 earthquakes, hundreds of small steam-blast explosions, and the outward growth of the volcano's entire north flank by more than 80 meters. A magnitude 5.1 earthquake struck beneath the volcano at 8:32am on May 18, setting in motion the devastating eruption.
Within seconds of the earthquake, the volcano's bulging north flank slid away in the largest landslide in recorded history, triggering a destructive, lethal blast of hot gas, steam, and rock debris that swept across the landscape as fast as 1,100 kilometers per hour. Temperatures within the blast reached as high as 300 degrees Celsius. Snow and ice on the volcano melted, forming torrents of water and rock debris that swept down river valleys leading from the volcano. Within minutes, a massive plume of ash thrust 19 kilometers into the sky, where the prevailing wind carried about 490 tons of ash across 57,000 square kilometers of the Western United States.

Even though temperatures within the blast reached such high temperatures, the haze produced by the dust, ash, and smoke from the eruption blocked the sunlight and caused global temperatures to drop by 0.1 OC. However, the pattern of warming or cooling from a volcano is not always simple. Climatologists with NASA have found that while volcanic eruptions can cause global cooling effects, they may also trigger seasonal climate warming. Computer models developed by climatologists have found that aerosols emitted during an eruption can absorb heat, and cause warming of the troposphere (lower atmosphere) in the winter. The pattern of cooling or warming also depends upon how much sulfur dioxide is emitted from the volcano. Major eruptions that produced large amounts of sulfur oxides (the eruption of Mt. Pinatubo in 1991, for example) contributed to significant global cooling, whereas eruptions that emitted only a small amount of sulfur dioxide to the atmosphere did not significantly lower global temperatures.




Volcanoes can also have long term effects on climate and Earth's spheres. Volcanic debris can break down fertile soil, making it difficult for plants and crops to grow. Endangered animals may be pushed to extinction, which causes disruption to the ecosystem and a loss of biodiversity.

One of the most well-known eruptions was the volcano Krakatoa in 1883. Krakatoa is located in the Pacific Ocean. The eruption was so powerful that its effects were felt across the world. Dust and particles caused copper-colored sunsets over much of the world for two years. Sulfur dioxide spewed out by the volcano caused the average temperature on Earth to drop by at least a degree. While one degree doesn't sound like much, that change is enough to disrupt sensitive ecosystems.

Global cooling related to major volcanic eruptions typically lasts for one to two years after an eruption occurs. Over an even longer period of time, volcanic activity slowly releases carbon dioxide from rocks in the Earth's mantle and crust. Despite the small contribution of such volcanic carbon emissions, it does affect the overall distribution of carbon dioxide and leads to global warming over long periods of time.



Sources
http://pubs.usgs.gov/gip/volcus/ustext.html (public domain)
http://eob.gsfc.nasa.gov/Features/Volcano/
http://pubs.usgs.gov/gip/volc/people.html (public domain)
http://cnx.org/content/m23176/latest/ (CC BY)
http://www.dailymail.co.uk/news/worldnews/article-1203028/Will-Krakatoa-rock-world-Last-time-killed-thousands-changed-weather-years-deadlier.html (fair use)