The collision of the Indian and Eurasian plates measured with GPS. GPS data from Gan et al 2004.
It’s not an exaggeration to say that the theory of Plate Tectonics completely and utterly revolutionised the way we think about the sphere of slowly churning rock that we call home. Earth’s surface is in constant motion – continents repeatedly colliding and then splitting apart. Today, the motion of tectonic plates can measured extremely precisely with satellites; these measurements can be used to predict the distribution of earthquake and volcanic hazards. My research is focused on understanding what happens when continental plates collide or are ripped apart.
The Indian plate has been colliding with Eurasia for the past 50 Million years or so. As India has ploughed northward, it has created the Himalayas and the vast Tibetan plateau ahead of the collision front. GPS measurements show that the impact of India can be felt more than 2000 km from the Himalayas – this causes devastating earthquakes over a wide zone. Short-term earthquake prediction seems impossible, but all earthquakes are preceded by a slow build-up of tectonic strain around faults in the crust. I have been developing methods for mapping this strain using the latest radar satellites. The aim is to use this new technology to identify areas that might be prone to future earthquakes.
The African plate is being ripped apart along the Great Rift Valley. In Ethiopia’s remote Afar desert in 2005, a 60-km-long portion of the rift opened by as much as 10 metres, as molten rock was intruded into the crust. In the 8 years since this “rifting episode” began, we have seen 14 separate intrusions, and three volcanic eruptions. The geological fireworks in Ethiopia are the birthing pangs of a new ocean, as the Horn of Africa separates from the mainland over the next few million years – a blink of the eye to a geologist. Understanding the processes in Ethiopia is also helping us learn about volcanic hazards in Iceland. A repeat of the massive 1783-4 Laki eruption today could kill more than 100,000 in Europe.
The discovery of plate tectonics
The consequences of movements within the Earth’s crust – earthquakes – have long been of interest to science because their destructive effects could be so profound. Lisbon, a major European city, was completely destroyed by an earthquake in 1765 and a subsequent tsunami and fires. The event was widely reported and studied in the Royal Society’s Philosophical Transactions in what would become the first stirrings of modern seismological science. Later earthquakes would be studied using the most up-to-date tools available to science. The Society financed the 19th century engineer Robert Mallet in an expedition to record the Great Neapolitan Earthquake of 1857 in which Mallet recorded its aftermath in photographs.
But the mechanisms behind these events were not understood. Some of the earliest speculations about the Earth’s interior were made by Edmund Halley in 1692, based upon evidence provided by the ‘wandering’ northern magnetic pole. It was not until the early 20th century that ideas of continental drift were discussed. A symposium on continental drift was held at the Royal Society in 1965 and this marks the beginning of plate tectonics as a mainstream topic within the scientific community and an explanation for earthquakes, volcanoes and many other phenomena.
Dr Tim Wright is a University Research Fellow at the School of Earth and Environment, University of Leeds. His work is on the physics of continental deformation and the earthquake cycle.
The 'discovery of plate tectonics' section of this article was written by staff at the Royal Society.