David has studied the "DNA of rocks"

2016-01-27

David Budd ontop of Mount Merapi, Indonesia. Photo: Börje Dahrén

David Budd has studied what he refers to as "rock-DNA". He says lava and ash created during past volcanic eruptions can tell us a lot about the hidden processes that operate within the Earth’s crust, and that eventually lead to an explosive eruption. Importantly, this information can also tell us how the magma plumbing system looks, thousands of meters below the surface of the Earth. With this knowledge, David hopes we can be better prepared to forecast future eruptions, and in the long run, maybe even save lives.

Active volcanoes pose a major and direct threat to people living close by, but an eruption may also cause massive damage at a greater distance. One example was the cataclysmic event at Toba, one of this planet’s largest supervolcanoes, located on the Indonesian island of Sumatra, which erupted about 75 000 years ago. The volcano released about 2,800 cubic kilometers of volcanic material, and the ash was spread over Southeast Asia, India and the Arabian Peninsula, dropping the global mean temperature by several degrees.

Even today, Indonesia is one of the world's most volcanically active areas, and also one of the most densely populated. The fertile soil attracts communities to live on the volcanic slopes to grow their crops. However, sometimes this decision costs them the ultimate price.

In 2014, the Indonesian volcano Kelud had a large explosive eruption, and over 85 000 people had to be rapidly evacuated. David Budd has examined minerals from lava and ash from this eruption, and also from the supervolcano Toba, and from Katla in southern Iceland.

To understand why some volcanic eruptions occur suddenly, and without much notice is a very important part of volcano monitoring and disaster risk reduction. David Budd has been able to draw several important conclusions about these dangerous volcanoes by studying eruptive material from previous eruptions using advanced petrological analytical tools. 

- Before an eruption occurs, magma is often stored in the upper crust beneath the volcano. Here, at high pressure and temperature, dynamic interaction processes that affect the magma composition take place, which act to influence the eruption style and behaviour, David explains.

- For example, if the bedrock surrounding the magma chamber is hydrated (water-rich) and thus easily melted, it can substantially increase the water content of the magma if it becomes assimilated, likely increasing the explosive potential of the volcano, he says.

To better understand the processes that cause explosive events at the Indonesian and Icelandic volcanoes that David visited, he has analyzed the rock samples using several different methods, and importantly, at the crystal level.

Using thermobarometic modeling, a method based upon the fact that minerals vary in composition as a function of temperature and pressure, David and his collegues found that the magma plumbing system below Katla is very shallow. This has of course serious consequences, because the shallow magma storage can lead to eruptions with only a short onset time, and few pre-eruptive warning signals.

In addition to the mineral composition, David also studied oxygen isotopes within the mineral samples. This isotope system reveals important information about evolutionary processes that occurred within the magma plumbing system, right up to eruption. For example, David’s analysis revealed signs of shallow-level assimilation of hydrothermally-altered caldera material just before the explosive eruption of Toba supervolcano. This late-stage process, he says, may explain the extreme explosiveness of the eruption.

David Budd defended his thesis "Characterising volcanic magma plumbing systems: a tool to improve eruption forecasting at hazardous volcanoes" on January the 22:nd. 

Download the thesis

/Katarina Sundberg

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