The Tsunami Situation

Tsunamis are highly destructive waves triggered by underwater disturbances such as earthquakes, volcanic eruptions and landslides and so far have been unfairly overlooked in my blog. The mechanism that triggers these events is simple – increasing or decreasing the load atop the Earth’s crust initiates stresses and strains. As previously explained, shifting volumes of water can act as a heavy enough mass to generate crustal rebound.

At the end of the last ice age, a monstrous underwater landslide named the Storegga slide erupted off the coast of Norway (Ataken and Ojeda, 2003).  As a result, parts of Norway, Scotland and Iceland were inundated by the giant tsunami wave of 25 meters in height that hit after approximately 3200 cubic km of seabed was displaced at the continental shelf. Ice melt in Northern Europe is held responsible for causing a sequence of earthquakes that culminated in the immense landslide. Contemporary studies have uncovered that Storegga was one of many strong megaslides caused by glacio-isostatic rebound in the aftermath of ice ages (Bryn et al., 2002).  Over the last 1.3 million years, the Storegga area has been a hotspot for sliding due to the dominance of glacial/inter-glacial cyclicity.

A more recent consequence of underwater sliding occurred in 1998 when a tsunami killed 2000 in Papua New Guinea. At the time, Papua New Guinea was experiencing an extreme drop in sea level due to the prevailing El Nino conditions (Hasegawa, 2010). This leads one to believe that if rising and falling sea level triggers more earthquakes in coastal areas, the frequency of underwater slides and tsunamis is sure to increase.  

What Are The Long Term Trends?

Supporters of the theory that anthropogenic climate change could trigger a greater number of earthquakes are likely to refer the long term record of earthquake events. I came across the graph below from a USGS ‘Earthquake Project’ which aims to analyse earthquake trends. The figure clearly shows that in recent years the number of all earthquakes has shot up.

However, a graph like this can be misleading. For one thing the scale merely spans a 30 year time frame dating back to the mid-1970s therefore is unsuitable for assessing long term trends. More importantly, this ascending pattern can be suitably associated with the launch of a global network of seismograph stations capable of discerning low intensity earthquakes. Such ground movement was undetectable up until 25 years ago. A solution is to include only the earthquakes reported to be magnitude 7 or above – all these events would have been detectable with fewer stations using less advanced technology.  Nonetheless, it is difficult to ascertain how accurate the earthquake record is during the 19^th century. There is likely to be some incomplete data, therefore data sets may underestimate the occurrence of earthquakes before 1901. I have found that it is important to consider that this field of science is riddled with uncertainties and that a long term hazard record must be scrutinised. 

The data below comes from the USGS. The relatively long time ranges (38 years) summarise how earthquake activity since 1901 has been continuously increasing. Having excluded all low intensity events, the figures suggest that more major earthquakes are occurring now.

1901 to 1938 - 53 earthquakes

1939 to 1976 - 71 earthquakes

1977 to 2014 (2011) – 164 earthquakes

Is this upward trend enough to make us believe that nature has finally risen up to combat human domination? Too many scientists surmise that the data above is tangible evidence to prove that the trend will continue to climb. The effects that anthropogenic climate change has on the inner workings of the Earth are far from certain and past events must be interpreted with consideration. Unquestionably the statistics allude to the fact that we are in a period of increased tectonic activity, but without establishing the cause it is unclear whether this trend will be sustained.  

A Brief Adjunct

In addition to the ways in which humans indirectly steer crustal dynamics through their adverse effect on climate, certain other anthropogenic activities must be considered. Namely mining, oil extraction and the building of dams, which are figureheads of anthropogenic mastery over the Earth’s natural resources. Previously my account had been exclusive to hydrospheric processes affecting predominantly oceanic fault lines. It is important to add that sizeable constructions can also alter the strain on tectonic plates and lubricate fractures enough to shake the ground.

Crustal Vengeance: evidence to support human influence on geological hazards

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.

http://www.amazon.co.uk/Waking-Giant-changing-earthquakes-volcanoes/dp/0199592268

Climate Change: a Groundbreaking Topic?

As little as 30 years ago scientists were still puzzling over the effect humans had on the earth and what was in store for future generations. It was then not until 1990 that the first Intergovernmental Panel on Climate Change assessment was completed and certainty was expressed concerning the warming effect of CO₂, methane, CFCs and nitrous oxide emissions. Needless to say, climate change science is rife with disputes and confusion. At first, populations struggled with accepting that their daily energy consumption could be dominating the climate system of our own planet Earth, causing global temperatures and sea level to gradually eclipse natural fluctuations.

But is it too much to ask the public to accept that now their actions are causing major changes in the Earth’s crustal properties that could result in an increased frequency of geological hazards? It seems like nothing in today’s environment is immune to climate change, but can this atmospheric force wield enough power to influence tectonics and seismicity beneath our carbon footprints? The reading I have done prior to starting this blog has illuminated that this field of climate science is considerably split by a large divergent boundary.

On one side are those who see the concept to be a mere fabrication by the so-called global warming alarmists who seek to plaster climate change propaganda over every global disaster. The recent suggestions that the Japanese tsunami and the Haiti quake could be linked to climate change have been met with laughter amongst climate sceptics. Up until now, climate change cannot be accused of causing any direct casualties; perhaps a reason why its threat is scorned by so many. Studies have shown that whilst public acceptance of climate change is high, many still lack concern over a problem that is ‘too distant’ to affect them. It is much harder however to come to terms with the fact that your actions have indirectly taken the lives of millions of victims on the other side of the globe.

In an online article Paul Joseph Watson mocks:

“Earthquakes are called natural disasters for a reason – they are not caused by emissions of that deadly, poisonous, toxic, hateful gas known as carbon dioxide, the life-giving substance that humans exhale and plants breathe.”

Stereotypically, advocates of climate change have an inflating archive of exaggerated claims as Watson sarcastically alludes to. Whilst it is easy to disregard this theory as yet another apocalyptical manifestation, I implore you to examine the mounting scientific evidence that indicates that human induced geological hazards are not imaginary. Is it time to accept that hazards aren’t as natural as they used to be?

Currently my position within the debate is firmly central. Despite beginning initially unconvinced, my first plunge into the literature has unearthed several convincing studies, which I will address in my next post. Conclusively, this blogumentary will follow my exploration into this emerging environmental topic which I hope will be enjoyably pursued by budding climate scientists to those of you who are keen to know if the survival techniques learnt in the film 2012 will ever be put to use.