Read all seven of the biggest mysteries about Earth
Explore an interactive map of our Unknown Earth
Volcanic eruptions and earthquakes are tangible proof that we live on a planet made up of fidgeting tectonic plates. Since most faults and volcanoes occur along plate boundaries, it is fairly easy to predict where in the world they will happen. Unfortunately for the people who live near to them, working out when is more complicated.
Advertisement
Long-term probabilistic predictions of earthquakes based on what has happened in the recent past are not too much of a problem. People living in the San Francisco Bay area, for example, know that there is a 62 per cent chance of a major earthquake there in the next 30 years. Short-term warnings 鈥� on the scale of seconds 鈥� are also now becoming possible. Japan recently launched just such a system, which aims to give people enough time to run for cover or dive under a table.
While these kinds of measures can undoubtedly save lives, it would be more useful to have warnings on timescales of weeks or days, to evacuate the areas most at risk. If the Earth gives out warning signs on these timescales, however, no one has yet worked out how to read them.
Mainstream attempts to forecast quakes usually involve models of the stresses and strains on a given fault, estimates based on when the fault last moved, and satellite measurements of ground motion. More controversially, some researchers believe that electrical disturbances on the edge of the Earth鈥檚 atmosphere 鈥� which some say have preceded a number of major earthquakes 鈥� could also be used as a predictor. The idea is that changes in stress leading up to an earthquake could increase pressure on rocks in such a way as to induce electric currents. These could trigger a release of radon gas or alter surface temperatures and ultimately affect the Earth鈥檚 electromagnetic field in such a way as to be detectable by satellites. Strange cloud formations above faults immediately before earthquakes have also been suggested as a possible warning sign.
While accurate earthquake forecasts are still a way off, it is becoming possible to predict when volcanoes will erupt. Recent advances in our ability to decipher the warning signs has led to a number of successful evacuations. Three months before the dramatic eruption of Mount Pinatubo in the Philippines in June 1991, for example, scientists detected tremors on its flanks. Soon after, the volcano started steaming and puffing out clouds of ash. As activity increased the government ordered an evacuation of 60,000 people, saving thousands of lives.
鈥淚t is becoming possible to predict when volcanoes will erupt鈥�
While not all volcanoes give such clear signals, even the smallest of signs can be now be used to predict eruptions. Subtle changes in the sound of the ocean were successfully used to forecast the eruption of Piton de la Fournaise, on the island of R茅union in the Indian Ocean in July 2006 and April 2007. Scientists monitoring the low-frequency seismic waves generated by the ocean hitting the sea floor had noticed that when an eruption was imminent, sound waves passing through magma chambers slowed down. Based on this observation, local people were evacuated with several days鈥� warning.
Keeping an eye on the weather could also aid predictions. Pavlof, an active volcano on the Alaskan peninsula, is most active during the autumn and winter. One explanation is that the storms at this time cause water levels to rise around the volcano, squeezing the magma up like toothpaste out of a tube. It is possible that climate change could have a similar effect. Melting ice sheets and rising sea levels will change the loads on earthquake faults and the flanks of coastal volcanoes, and could make quakes and eruptions more likely.
Worse still is the prospect of another supervolcano eruption. The last, 75,000 years ago, plunged Earth into a volcanic winter for hundreds of years 鈥� and wiped out 60 per cent of the global human population.
Eruptions occur every few hundred thousand years so we know another is on the way. The two main candidates are being monitored 鈥� Yellowstone in Wyoming, and Campi Flegrei in southern Italy 鈥� but no one knows when they will blow. Perhaps that鈥檚 a good thing, as there is nothing we can do to stop them.
