Wednesday, 6 November 2013

Volcanoes: Flatulence of the Earth

If I had to take a guess at what really got the whole idea of “science” going, and if that motivator was some singular event, I think the safe money would be on a volcanic eruption. I imagine some early human scratching his head and looking on with an expression of dumbfounded awe as a pyroclastic flow swept past at 100 km/hour, simultaneously burying him in a heap of ash and debris and cooking him at a temperature up to 700 degrees C.

Whether they are entombing cavemen, spewing lava into the air, or simply dominating the horizon volcanoes are one of the few things that both the average person and the most devoted nerd can agree are just plain awesome.

Volcanoes come in three main varieties: spreading centre volcanoes, subduction zone volcanoes, and intraplate volcanoes. Each is the result of intense pressure deep within the Earth and the mechanics of tectonic plates.

To really understand volcanoes you need to understand plate tectonics. Since this article is meant to focus on the former, I will sum up the latter in a single sentence: The Earth’s surface is made up of enormous plates that fit together like a badly made jigsaw puzzle, moving around and smashing into each other to produce all the features of the planet’s landscapes.

When plates pull apart from one another, hot rock from beneath bubbles to the surface and you get a spreading zone volcano. 

When two plates smash into each other, one is forced beneath the other (AKA subduction) where the pressure and friction cause the rock to melt. Eventually that rock finds its way up through cracks in the surrounding material to the surface and you get a subduction zone volcano. 

When you have a plate with a weak spot and some particularly hot and motivated magma beneath it, you get an intraplate volcano.

Beyond that, volcanoes don’t like it when you try to come up with general rules about them. Spreading zone volcanoes tend to be the least explosive, but Iceland is really just a combination of these sorts of volcanoes and explosive eruptions there have halted global air traffic and cost the world economy billions of dollars. Intraplate volcanoes tend to be the most destructive, but the Hawaiian hotspot has been quietly erupting more or less constantly for at least the past thousand years.

Clearly, volcanoes are full of surprises. Unfortunately they are rarely the kind of surprises that you look forward to. In 1980, volcanologists in Washington state watched and waited while Mount Saint Helens swelled and rumbled, expecting either an impressive vertical eruption or for the volcano to slowly go back to sleep. No one predicted the lateral (sideways) explosion of ash and debris that killed 57 people and flattened 200 square miles of forest.

The most recent surprise that volcanologists have unearthed is one that they seemingly should have discovered quite a while ago. On September 6, 2013, scientists announced that they had discovered the largest volcano on Earth (so far). Tamu Massif as the peak is known rises 3.5 km from the sea floor about 1,600 kilometers east of Japan and occupies an area of 310,000 square kilometers, making it about the size of the British Isles. The volcano formed over millions of years as eruptions piled up one on top of another and collapsed outwards and upwards, although the summit still lies about 2,000 meters (6500 feet) beneath the waves.

Tamu Massif is being compared to another massive volcano called Olympus Mons which is found on Mars and still holds the title of “biggest volcano in the solar system.” Until now, mountains as big as Olympus Mons were not thought to exist on Earth. The reason is took so long to find the behemoth volcano is that the world’s oceans are one of the few things that are less well understood than volcanoes themselves. Also, scientists originally thought the formation was the result of multiple volcanoes joining together. The recent breakthrough was in establishing the existence of a single vent responsible for forming Tamu.

It’s pretty incredible to think that something like the world’s biggest volcano could exist beneath the ocean, unknown to people, until the 21st century. It really makes you wonder what other incredible things lay hidden by water and question whether or not it’s a good idea to keep dumping radioactive waste and movie directors into the depths.

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