Picture, if you will, the dominant feature of a volcano looming over a vast forested landscape with mountains and streams. The raw power hidden just a few measly kilometers beneath the surface is shrouded by the majestic beauty of the snow-capped cone, evoking many deep emotions with just a simple geologic phenomenon. Then, with out warning, a small cloud erupts from the top, blasting rock fragments as far a ten miles away (Newson, 1998).
Having cleared the igneous-based cork out, the volcano unleashes its full load: a five-mile high cloud of superheated steam, gases and ash conglomerations bubbles up in just hours. The local area is devastated by the eruption. However, with a few repeated eruptions within days of this initial one, the volcano will have a more global effect that will reverberate across the human populous in a much more dramatic way; climate change.
Our world is dotted by various cones and calderas in and around the multiple plate boundaries that crack their way through our planet's outer shell like the ones in a dropped china plate. Along with earthquakes, these zones of tectonic activity produce most of the world's volcanoes. At many of these boundaries the plates move apart, allowing for magma to build upward to the surface from the mantle. Other boundaries, called subduction zones, force one plate to move under the other, carrying organic wastes and ocean water with them.
These produce the most non-rare, violent eruptions because the materials from the sub ducted plate mix with the magma to produce gasses and water vapor, which add pressure tot he underground magma fields and make them much more explosive when finally exposed to the colder surface air (Redfern, 1999). Mt. Saint Helens, Pinatubo, and Krakatau are all stewing over these boundary types, which have all been noted to produce dramatic damage to their respective regions and to produce climate shifts.
Still one other volcano type of great concern to many scientists are the super-calderas, as they are called, because of their volatile nature and unpredictability. Ironically, these super-volcanoes are thought to be produced in the same manner that Hawaii's volcanoes are, which are some of the most unobtrusive volcanoes on our globe. Within the mantle, giant plumes of magma, sometimes as large as cities such as New York or Tokyo, build up underneath the crust, trying to push through. There they remain, push with ever-increasing pressure, until they burst through the crust out into the atmosphere. They are referred to as super-volcanoes because their sheer eruption size dwarfs even our most volatile contemporary eruptions.
Yellowstone is a noted example of a young caldera in the Untied States, as is Mt. Toba in Indonesia. Both have erupted many times in the past, and have caused dramatic climate changes when their excrements held high aloft by the winds blotted out sunlight around the world and lessened temperatures to the point of an ice age. Mt. Toba erupted about 75000 years ago, and shattered that part of the Southeast Pacific (Newson 1998). It may be the cause of a glaciation (a period of lessened global temperatures and intense cold in the high latitudes that favors the formation of continental ice sheets) that inundated the world around that time. Yellowstone has also caused massive temperature drops, but is now overdue for an eruption, leading some to fear the worst is yet to come.
So what causes the volcanoes to produce climate changes? In order to understand that, it is necessary to understand the basics of our atmosphere and its structure. There are four main layers based on the change in temperature from the bottom to the top of each; the troposphere, stratosphere, mesosphere and thermosphere. Our concern lies in the first two because rarely, if ever, does ash and debris ever make it beyond the ozone layer in the stratosphere. When a volcano explodes, it sends its ash deep into the atmosphere. By the force of pressure, it makes its first leap into the air.
Then the strong convection of heat upward carries it further and further (Aguado, 2004). Most explosive eruptions result in many cubic miles of debris being blown into the air, which means a lot of displaced matter in the air. Most of that matter, in the form of ash and pulverized rock fragments, gets scavenged by the frequent weather phenomenon that whip through the troposphere on a constant basis. Some, however, gets blown high into the stratosphere, which reaches beyond the grasp of the clouds and precipitation that would normally use it for condensation nuclei. There, it is kept aloft by the vigorous winds that whip like ropes across the planet, which means it gets distributed like a blanket over our heads.
The ash and debris will then start to react chemically with the air to form sulfuric acid and other compounds (Aguado, 2004). These reflect sunlight very well, especially the shortwave radiation. Incoming sunlight is mostly shortwave radiation to begin with, so in the presence of these compounds, it tends to bounce back into space. With less sunlight reaching the Earth's surface, lower temperatures result. What makes this a climatologically phenomenon instead of a meteorological one is that the acid compounds stay in the atmosphere for months on end, resulting in long-term temperature drops over a wide area.
If these drops become pronounced enough, as in the eruption of a super-volcano, then a glacial epoch could result. More frequent occurrences of explosive volcanic activity along the subduction faults can result in less dramatic drops, however they are not to be taken lightly, as even minor drops could and often do result in wacky weather conditions around the world for years to come. Mt. Pinatubo, when it erupted, released two cubic miles of debris into the atmosphere and caused a one degree Celsius drop for a whole year, resulting in some rather extraordinary weather events (Newson, 1998). Another example is 1816, deemed the "year without a summer" because of the 1815 eruption of Mt. Tambora in the East Indies (Redfern, 1999).
Bibliography
Newson, Lesley. Devastation: The World's Worst Natural Disasters. London: Dorling Kindersley, 1998.
Redfern, Martin. Planet Earth. New York: Larousse Kingfisher Chambers Inc., 1999.
Aguado, Edward., and James E. Burt. Understanding Weather and Climate. ed. 3, Upper Saddle River: Pearson Education, Inc., 2004
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