As a response to the eruption of the Mount Nyamulagira in Congo and the following fears of an imminent eruption of the Nyiragongo volcano, scientists and local authorities were using a long series of space images from ESA's Envisat to monitor the situation and take the appropriate decisions. Using the Advanced Synthetic Aperture Radar (ASAR) on Envisat, the lava flows were mapped by comparing images acquired over the area before and after the eruption, while the ground deformation was mapped by the 'SAR interferometry', or InSAR technique. The satellite observation proves undoubtedly its utility in cases of volcano eruption.
On 2 January 2010 Mount Nyamulagira in Congo erupted, threatening the population living in the town of Sake. After this event, there were fears that the Nyiragongo volcano, which devastated the city of Goma in 2002, would also erupt. Moreover, lava from the Nyamulagira eruption was flowing in a direction south and southwest of the volcano, raising thus concerns that lava could cover the Goma and Sake roads within weeks, causing problems to the local economy.
Following these events, scientists and local authorities used a long series of space images from ESA's Envisat, together with seismic and helicopter data, to monitor the situation and calm fears of the local population. In the case of volcano eruption, optical and radar instruments can image the various associated phenomena such as lava flows, mud slides, ground fissures and earthquakes, while atmospheric sensors can identify the gases and aerosols released by the eruption, and quantify their wider environmental impact.
As regards lava flows, it can be mapped by comparing satellite radar images acquired before and after the eruption by the Advanced Synthetic Aperture Radar (ASAR) on Envisat. The information about the size, direction and speed of the flow of the lava from the Nyamulagira volcano was crucial for enabling the authorities to make timely decisions.
Regarding the ground deformation caused by the volcanic eruption, the scientists used a technique called "SAR interferometry", or InSAR, to construct an "interferogram" image by analysing the differences between two radar signals taken over the same area on Earth at different times. The InSAR technique was also applied to data over Mount Nyiragongo to determine whether there were any signs of abnormal activity at the volcano.
In order to evaluate the level of risk and increase their knowledge of volcanoes, volcanologists need continuous data over long periods and, in some cases, only a satellite is capable of providing this because of the inaccessibility of the areas.
More information at:
http://www.esa.int/esaEO/SEM3UUKOP4G_index_0.html