Friday, August 17, 2007

An Unstable Earth?

I came across an interesting article, referenced below, which suggests that we may expect trouble from within the Earth itself, in addition to the surface effects of climate change involving mainly the atmosphere and the seas. According to the geologic record, the interglacial periods are separated by around 100,000 years, and are inter-spaced by the ice-ages. The exact causes of ice-ages remain a matter of considerable speculation but are generally thought to relate to changes in the Earth's orbit around the Sun, and hence to variances in the amount of solar radiation falling onto the Earth.

As an ice-age progresses, glaciers advance in varying degrees from the polar regions in the direction of the equator, resulting in substantial proportions of the continents becoming covered in sheets of ice with a thickness of more than one kilometer. Now that is an amazing thought! To achieve this phenomenon, water is drawn from the oceans and frozen into ice. Correspondingly, the sea levels globally were anywhere up to 130 metres lower than they are today. Given the relatively shallow basin of the English channel and that between Alaska and Russia, it was once possible to walk between the various continents.

At the end of an ice-age, the ice-sheets retreated and so the melt-water drained back into the ocean basins, causing the sea levels to rise at a rate of several metres per century. Significantly, research by Bill McGuire, who is director of the Benfield UCL Hazard Research Centre, shows that in the Mediterranean area, there exists a good correlation between the rate of rise and fall of sea levels during the last ice-age and the number of volcanic eruptions in Italy and Greece. The connection was clearest following the retreat of glaciers which occurred around 18,000 years ago, resulting in extensive flooding of the globe, and an increase in sea levels to where they are now, with a corresponding 300% increase in the number of volcanic explosions in the Mediterranean region.

Now correlation does not necessarily reveal cause, but the following explanation has been offered to account for these findings. The huge mass of melt-water pouring onto the continental margins and marine island chains (where over 60% of the world's active volcanoes are) squeezes and distorts the Earth's crust, forcing-out underlying magma into an actual eruption. There is considerable variation in results from mathematical models as to the extent of sea level rise that might occur in the future, but it seems quite possible that hair-trigger volcanoes (those close to blowing their top) might be set-off by relatively modest increases. Sea-level rise is in itself a dangerous thing, since a one metre rise would threaten to inundate about a third of all agricultural land in the world, two metres would overwhelm the Thames flood-barrier under surge-conditions, while four metres would swamp Miami, placing it 60 kilometres off the US coast.

The higher that sea levels increase, the greater is the chance that the world's volcanoes may be triggered, and in extreme cases, the activation of geological faults could occur, resulting in more earthquakes and undersea landslides. Hence there is a tsunami risk too, for example the Storegga Slide off Norway 8,000 years ago, which sent a 20 metre high wave across the Shetland Islands and onto the east coast of Scotland. The whole notion brings to mind that the Earth is not a collection of unrelated parts but an holistic entity (the "Earth system"), wherein change in one feature may have ramifications through the whole planet.

Related Reading.
"The Earth Fights Back," by Bill McGuire, Guardian Unlimited August 7, 2007.


Anonymous said...


Anonymous said...

I see destruction nearby,God help us