Philippines Volcano - Global Impacts?
Posted by JAC on 12/23/2009, 10:01 am
Dr. Greg Forbes, Severe Weather Expert


As I write this on Tuesday December 22, a volcano in the Philippines -- Mount Mayon -- is
threatening to erupt. It has triggered more than 2000 small earthquakes as the lava works its way through cracks in the rocks to the Earth's surface, and sulfur dioxide emissions are running about 12 times normal. Both of these are signs of an imminent eruption. It has had some small lava flows and puffs of smoke in recent days, another sign of an imminent large eruption.

The map below shows a white dot at the location of the Mayon volcano. It is within a corridor of active earthquakes and volcanoes known as the "ring of fire." This ring is along the western and northern edges of the Pacific Plate, a slab of the Earth's surface that is slowly (a couple of inches per year) sliding northwest relative to the adjacent plates. There are some smaller plates in the Phillipines between the Pacific Plate and Eurasian Plate, getting the "squeeze play" between the two, and extending the ring of fire into this region as well.






Earthquakes develop in the ring of fire (and elsewhere) where different plates rub together in different directions or speeds. The rock along the interface gets put under stress or stretched until it snaps. The rock on either side of the snap -- or "fault line" -- then sharply moves in what we call an earthquake.

Volcanoes also occur along the ring of fire at these plate collision zones when the plates are also moving toward each other. Some of the horizontal convergence is used to form mountains as rock is pushed upward, but some of the near-surface crust of the Earth (lithosphere) is also forced downward over millions of years in what is called a "subduction zone." The figure below shows what happens in the subduction zone, with some of the rock material being driven 50-100 miles below sea-level.







That slab of sinking rock gets put under such intense pressure from the weight of the rock above that it reaches a temperature of around 2000F and liquefies. This is much like iron, steel, and other metals can be poured as a high-temperature liquid into moulds. Some of the materials in the lithosphere layer (such as water and fossils) can be heated into gases like water vapor, carbon dioxide, and sulfur dioxide.

The volcano forms as some of that liquefied material and gases begin to work their way upward through cracks in the rock above, as shown below in the red bubbles or plumes. This liquid material beneath the surface is called "magma", then called lava as it comes out at the surface








Mount Mayon is a nearly perfect cone-shaped mountain, formed from previous volcanic activity (depicted in figure below). Geologists consider it the most perfectly cone-shaped of the world's volcanoes. It's the most active of the volcanoes in the Philippines. It has erupted 49 times since the first documented eruption in 1616. It's most violent eruption was in 1814, when more than 1200 people were killed. Its last major eruption was in 1993.







The Mayon volcano poses tremendous hazards in its immediate vicinity, of several potential types. Past eruptions have been in various forms, some with flowing lava. Some eruptions have been explosive and shot rocks into the air and down at distances away from the volcano. Some have resulted in destructive mudflows (lahars). And there has even been a nuee ardente - a destructively fast flow of deadly superheated air filled with a dense concentration of choking dust. Evacuation orders are in effect.

Volcanoes in the Hawaiian Islands, by contrast, are predominantly of the flowing lava type due to a different chemical composition of the magma. Mount St. Helens in Washington was of the explosive type.

Which form, and how intense, the imminent Mayon eruption takes is not known. But at its extreme it could have global environmental ramifications. If the explosion is upward and intense enough to send dust and sulfur dioxide particles (aerosols) into the stratosphere (roughly above 50,000 feet), it could have effects that last for several years.

An explosive eruption of Mount Pinatubo in the Philippines in 1991 was of that type. It resulted in a warming in the stratosphere, and a near-surface cooling of about a half degree Fahrenheit globally (a fraction more in the Northern Hemisphere) for about two years. The near-surface cooling results from reflection of sunlight off the dust and sulfate aerosols, so less sunshine to warm the ground and air nearby. Thus, explosive volcanoes are one way that the Earth can offset global warming.

Those aerosol and dust particles result in some spectacular red sunsets around the globe. But the sulfates in the stratosphere are one of the agents that can result in accelerated destruction of the ozone layer. A bit more ultraviolet radiation gets through, with its risks of sunburn and skin cancer.

So we all have a reason to be interested in the nature of the eruption of a volcano half way around the world! And let's hope for the best for the Philippines. They have suffered terribly this year from flooding from several typhoons. They don't need another disaster!


Posted at 4:45 pm ET
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Mayon activities intensify - JAC, 12/18/2009, 1:18 pm
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