Tectonic Hazards

Discusses the dynamic and complex nature of Tectonic Hazards in terms of their relationship to the concept of risk. In specific:
Why is it difficult to assess risk in terms of tectonic hazards?
What is the concept of resilience?
What are the social and economic impacts of tectonic hazards?
Shifting to the consideration of mass movement hazards which often accompany tectonic hazards, discuss:
Slope stability;
The role of gravity and the role of water in mass movement events;
Whether or not one (gravity or water) can mitigate the effects or either (Gravity or water); How so?
Finally, explore triggering events related to potential mass movement events.
Can mass movement hazard predictions be made on the basis of understanding of slope stability and triggering events?

ANSWER

Tectonic hazards refer to a situation where the earth’s crust moves. The earth’s crust comprising both the continental and oceanic plate and the upper mantle combine to form a shell that is rigid and found at the surface called the lithosphere. The lithosphere separates into fragments referred to as tectonic plates where the meeting points is known as the plate margins. Movements of these plates are what becomes the tectonic hazard which scientists are still trying to find the cause. Evidence from geological sources indicates that these tectonic plates have been in the movement for at least 225 million years since the Pangaea split apart. The resultant effect was the formation of volcanoes and earthquakes and other related phenomena such as landslides and tsunamis. The first scientist to come across these events was Alfred Wegener in 1912 (Cloos 2009). Further development on the topic in the 1960s indicated that, “heat from the Earth’s core must cause the mantle material to move through the process of convection, and that it is these convection cells that drag the crust in different directions a few centimetres each year” (Cloos 2009). The entire premises of the movement is yet to be understood and contributions are made each day. This essay examines tectonic hazards in terms of their relationship to the concept of risk.

The risk that results from tectonic events become hazardous when they affect life. Statistics indicate that the population of the world has been growing exponentially and is further expected to rise to 9.7 billion by the year 2050. As population increases, more and more people are living in dangerous regions prone to a disaster resulting from tectonic movements. For instance, in the year 2015, an earthquake in Nepal missed the capital city Kathmandu by 80 kilometres. Should have the earthquake hit the city, the death rate would have been in millions rather than the ten thousand people that lost their lives. However, even with such huge risks, it is nearly impossible to predict tectonic events. So far, scientists use existing data to predict tectonic events on the hypothesis that the planet is bound to behave the same way in the next few ten thousand years. This is not always the case and sometimes the events are random and unpredictable making it fairly impossible to take precautionary measures.

The concept of resilience comes in to explain the nature of human societies. If people have to be able to live with the risk of tectonic hazards, resilience is their ability to withstand these events so that it does not become a hazard. A tectonic event only becomes a hazard when it affects or influences human activity. Using an arithmetic formula, risk reduction is the resultant figure when the product of mitigation of hazard and reduction of vulnerability is divided by the increase in capacity (Panza 2012). Mitigations are the means and methods design to prepare for possible tectonic hazards to reduce their effects. A community with proper mitigation strategies has stronger resilience to withstand the tectonic hazards.

Tectonic hazards have various social and economic impacts. On developed countries such as the United States, Europe and parts of Asia, tectonic events take a toll on the human development index (Alcántara-Ayala 2002). In less developed countries with high tectonic hazard rates, financial costs of damage increase dependency on international aid. The effects are more devastating on poorer populations with an income of less than $2 a day, where a tectonic event means that they no longer have access to necessities such as food, clothing and mostly, shelter. Tectonic events such as earthquakes have been known to cause absolute devastation and increase poverty levels in risky areas.

Slope stability, gravity and water mass movement all play a key role in determining the hazard level of a tectonic event. Gravity is the sole force that causes mass movement. It refers to the force that acts on the earth’s surface pushing objects towards it’s the centre of a planet (Lu 2008). On a flat surface, objects remain immobile under the force of gravity. However, on the occasion where the material forming the surface becomes weak, the mass that is unsupported moves downwards with respect to the force of gravity. On the other hand, in a slope, gravity is either resolved by an object moving perpendicular to the slope or tangential to the slope (Lu 2008). Whichever the movement, the effect is a tectonic caused landslide. Water is not always directly involved but contributes in either one of the following ways; firstly, water from rain adds weight on a slope. Weight is a force that causes stress and therefore slope instability (Lu 2008). Secondly, water is capable of changing a slope angle from a stable angle to an unstable one. Thirdly, masses of water can either be absorbed or adsorbed by soil minerals (Lu 2008). Whichever the process, the weight of the newly introduces molecules reduces stability or the surface frictional contact becomes reduced, also resulting in instability. Lastly, water contributes through the process of liquefaction where water oversaturated the sediment rocks resulting in loose sediment grain to grain contact as a result of water getting between them.

There are several known triggering events, some of them already discussed, for instance, mass increase in water, increased steepness of slope and gravity. Other events, mostly artificial are such as the removal of vegetation on the surface of the earth. Vegetation holds soil together and trees prevent direct action of the wind on the surface. Elimination of vegetation increases the hazard level of a tectonic event. Others are activities such as mining for fossil fuels buried in the earth’s crust, excavation, weaponry, nuclear energy among many others. However mass movement hazard predictions can be made based on an understanding of slope stability and triggering events but not to complete accuracy.

References

Alcántara-Ayala, I. (2002). Geomorphology, natural hazards, vulnerability and prevention of natural disasters in developing countries. Geomorphology, 47(2-4), 107-124.

Cloos, M. (2009). The nature of tectonic hazards. Volcanic and Tectonic Hazard Assessment for Nuclear Facilities (Connor, CB, Chapman, NA, Connor, LJ, Eds), Cambridge University Press, Cambridge, 24-73.

Lu, N., & Godt, J. (2008). Infinite slope stability under steady unsaturated seepage conditions. Water Resources Research, 44(11).

Panza, G. F., La Mura, C., Peresan, A., Romanelli, F., & Vaccari, F. (2012). Seismic hazard scenarios as preventive tools for a disaster-resilient society. In Advances in geophysics (Vol. 53, pp. 93-165). Elsevier.