EU researchers discover that magna build-up may put Salvadoran capital at risk

The team, comprised of VUELCO researchers from the University of Bristol, UK, and El Salvador’s Ministry of the Environment and Natural Resources, studied the density distribution beneath the Ilopango caldera and how tectonic stresses – caused by movement of tectonic plates along fault lines – have on the build-up of magma at depth. The findings have been published in the most recent issue of the journal ‘Nature Communications’.

A caldera is a large cauldron-like volcanic depression or crater, formed by the collapse of an emptied magma chamber. The depression often originates from very big explosive eruptions. In Guatemala and El Salvador, caldera volcanoes straddle tectonic fault zones along the Central American Volcanic Arc (CAVA). The CAVA is 1 500km long, stretching from Guatemala to Panama.

Specifically the Ilopango caldera is an eight kilometre by 11km volcanic collapse structure of the El Salvador Fault Zone. The collapsed caldera was the result of at least five large eruptions over the past 80 000 years. The last of these eruptions occurred around 1 500 years ago and produced enough volcanic ash to form a 15cm thick layer across an areas the size of the UK. The eruption was so powerful that it would have destroyed almost everything within a 100km radius, including a well-developed Mayan population. It also significantly disturbed Mayan populations as far as 200km away. The most recent eruptions were in 1879-1880 but were on a much smaller scale.

‘Most earthquakes take place along the edges of tectonic plates, where many volcanoes are also located,’ commented VUELCO project coordinator and co-author of the study, Dr. Joachim Gottsmann. There is therefore a link between the breaking of rocks, which causes faults and earthquakes, and the movement of magma from depth to the surface, to feed a volcanic eruption. The link between large tectonic fault zones and volcanism is, however, not very well understood.’

Previous studies have shown that magma accumulation before a large caldera-forming eruption, as well as the caldera collapse itself, may be controlled by fault structures. However, the research team states that it’s unclear to what extent regional tectonic stresses influence magma accumulation between large caldera-forming eruptions.

The team discovered that the current tectonic stress field promotes the accumulation of magma and hydrothermal fluids at shallow (less than 6km) depth beneath Ilopango. The magma contains a considerable amount of gas, which indicates the system is charged to possibly feed the next eruption.

‘Our results indicate that localised extension along the fault zone controls the accumulation, ascent and eruption of magma at Ilopango,’ said Dr. Gottsmann. ‘This fault-controlled magma accumulation and movement limits potential vent locations for future eruptions at the caldera in its central, western and northern part – an area that now forms part of the metropolitan area of San Salvador, which is home to two million people. As a consequence, there is a significant level of risk to San Salvador from future eruptions of Ilopango.’

Although these findings have only just been published, the VUELCO project officially ended in September 2015 and received just under EUR 3, 500 000 in EU funding. The project, a collaborative effort between European and Latin American researchers, devised global strategies for enhancing volcanic monitoring capacity, better data interpretation and the identification of reliable eruption precursors.

For more information please see:
project website