Human-induced global warming is unmistakably having an effect on the Earth’s ice and oceans: the melting of Greenland’s glaciers and the alarming sea level rise is well documented by the IPCC. However, what goes on beneath our feet is far harder to testify to. This has not prevented Bill McGuire of our Hazard Research Department here at UCL, from presenting evidence that has had many convinced that geological activity is increasing in response to global climate change. He along with six other authors complied a Theme Issue on 'Climate forcing of geological and geomorphological hazards' for the Royal Society. The aim of this blog entry is to introduce the arguments that support the notion that anthropogenic climate change could bring about a greater frequency of natural hazards.
Firstly, it is important to consider the role of glaciers and ice sheets on the Earth’s crust. Roughly 10.4% of the Earth’s surface is glaciated (approx 6,000,000 square miles), which exerts a significant weight upon the crust beneath. Consequently, the burden is lifted when ice melts allowing the crust to rebound (at a relatively rapid rate by geological standards). In tectonically active zones, rebounding crust could significantly alter stresses impacting earthquake faults and volcanoes. The Icelandic ice sheet Eyjafjallajökull sits atop a swarm of volcanoes of which would be triggered to erupt as a repercussion to any ice melt causing the unloading effect (Wadsworth, 2010).
The destabilisation of faults does not just trigger volcanic eruptions. The alteration of geological dynamics by loading and unloading of active faults elicits a ground-rumbling retort from the crust. Supporting evidence from history points to the melting of the Scandinavian ice sheets during the last Ice Age that prompted a succession of huge submarine landslides and tsunamis (McGuire, 2010). Whilst this seems to support the aforementioned theory, the concept is lacking in sufficient understanding about the actual nature and scale of the threat.
The distribution of meltwater adds another dimension to the problem, which is worsened by the rise in ocean temperatures, which causes water to expand through a process known as thermal expansion. The amalgamation of water acts as an added load on coastal fault lines. Its weight bends the crust which induces tension in the upper crust and compression lower down – a process McGuire likens to bending a plank of wood. The power of these forces can become strong enough to ignite catastrophic backlash. The winterly eruptions of Pavlof volcano in Alaska have been attributed to seasonal sea level rise causing compressional forces to release magma accumulated below the volcano. A study by Guillas et al. (2010) has revealed a correlation that links contemporary variations in El Nino Southern Oscillation (ENSO) to the occurrence of earthquakes in the East Pacific Rise (EPR). The observed 95% confidence interval is attributed to reduced sea levels in the eastern Pacific prior to an El Nino event that induced increased seismicity. This example illuminates how slight imbalances in the atmosphere and hydrosphere can shift environmental conditions enough to illicit a response from the Earth's crust.
Bill McGuire’s work has been influential to this field of science; his findings are soon to be published in his upcoming book ‘Waking the Giant: How a changing climate triggers earthquakes, tsunamis and volcanoes’. I anticipate this publication will be a benchmark in this emerging domain that links earth science to twenty-first century climate change. The link to the book’s Amazon page is provided below for enthusiasts who wish to delve further into the academic work surrounding the subject.
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