Where Grey Matter meets Dark Matter

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Episode 24 - 21 February 2010

How do you predict the future? Look into the past! At least, that's what Bob reckons.

Bob Spicer

Robert Spicer is Professor of Earth Sciences at the Centre for Earth, Planetary, Space and Astronomical Research at the Open University, in the United Kingdom. His research interests are in climate change on a geological timescale; in other words, how the climate of the earth has changed over the last couple of hundreds of millions of years.

Climate change is a big talking point at the moment, but there was a time when most of the earth was a tropical paradise. So one of the ways to find out how the earth might change as the globe warms is to dig into the fossil record and get an idea of how it was back when it was warm, ie, before the ice age(s).

Bob tells us about how and why the world was warmer and colder in the past - and also why this is no excuse for not doing anything about it now.



So... hot... The lava, that is. Source: MovieGoods

Dante's Peak. We all know it's a movie, but how many people have actually seen it? (It turns out that it gets better on subsequent viewings.) Another point that is not in contention is that Dante's Peak is about volcanoes. Big, fiery volcanoes. Dante's Peak (the town and the peak) are fictionally located in the Cascade mountains, co-incidentally near the real-life volcano Mt. St. Helens, which asploded in 1980.

Other real life volcanoes are found in Hawaii, which sits over a 'hot spot'. A hot spot is a point on the earth's crust that sits above a convection cell in the mantle (which is the stuff underneath the crust). The magma that is convecting upwards leaks out onto the surface and forms hot, runny lava. This runny lava forms shield volcanoes (which are relatively flat). They are pretty tame and don't tend to explode.

A hotspot sitting above a convection cell, with a nice shield volcano on the surface. Source: National Geographic.

Another type of volcano is found along sea floor ridges, where new crust is being made. The continental plates are ripped apart at this point which allows magma to boil up and then cool, forming new sea-floor. All in all, not much to worry about.

But Dante's Peak and Mt. St. Helens (along with Krakatoa and all the volcanoes through Indonesia and the Philippines and down the west coast of the Americas) are totally different beasts. They are part of the Pacific Ring of Fire, the edge of the Pacific plate which is being subducted under the surrounding plates. These subduction (or strato-) volcanoes are the big boys on the volcano scale. During subduction the lighter material on the surface is dragged down into the depths where it heats up. This contributes to the violence of the explosion, literally ripping the top off mountains and spewing hot rocks, ash and gas into the air and down the side of the volcano in the 'pyroclastic flow'. This stuff will not melt the flesh off your bones, it will disintegrate your entire body. It's a hot, noxious avalanche of death.

Stratovolcano picture showing the strata of lava and ash and crap that give it its name. Source: USGS.

But these modern day earth volcanoes are weak. On Mars, Olympus Mons is the biggest volcano in the solar system, 27 kms high and 550kms wide, but it hasn't worked for a while. And then there's the ultimate, badass, liquid-fire doom that giant rents in the earth's crust (called the Deccan Traps, located across most of north-western India) were spewing onto the surface in the good old days, around 65 million years ago. The people of Dante's Peak are just cry-babies.

This is from a modern (ie. weak) volcano in Iceland. To picture the Deccan Traps volcanic trauma, imagine this covering hundreds of thousands of square kilometers. Source: USGS

Oh yes: Molten rock underground is called magma. Molten rock on the surface is called lava. Don't get these two confused on pain of death.

Volcanoes - like pimples on the earth. But the pus is hotter, and more like acid.
Sources: First and Second


  • About hotspots and mantle plumes.
  • S. Rajan, Anju Tiwary & Dhananjai Pandey, The Deccan Volcanic Province: Thoughts about its genesis.
  • Bernard Chouet (28 March 1996) "Long-period volcano seismicity: its sources and use in eruption forecasting," Nature , vol. 380, no. 6572, pages 309-316.
  • Hotspots: Mantle thermal plumes". United States Geological Survey (05-05- 1999) http://pubs.usgs.gov/gip/dynamic/hotspots.html


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