Volcanic eruptions: Volcanologists working at the University of Bristol have come a step closer to discovering why some eruptions pop like a champagne cork and others ooze like toothpaste. Their work could provide better warnings of potentially explosive events like the eruption of Mount St Helens in the US.
Scientists have become very good at monitoring what goes on at the top of a volcano, but have always found it difficult to monitor the more important issue of what goes on deep underground, explained Bristol's Dr Jonathan Blundy. "It is much harder to track moving molten liquid at 900 degrees and several kilometres under the surface," he told a session at the BA Festival of Science at Norwich.
However, Dr Blundy, Dr Madeline Humphreys and colleagues developed a method to study events taking place under the volcano by studying hardened lava spat out by these fiery mountains. Details of their work were released yesterday and are published this morning in Nature.
They carried out their experiments on solidified lava from Mount St Helens, which erupted violently on May 18th, 1980, and from the Shiveluch volcano in Kamchatka, Russia.
When underground, the molten rock or magma contains 5 to 6 per cent water. While most of this bubbles up and boils off during an eruption, tiny droplets of water or "melt inclusions" are trapped inside the lava. Studies of these inclusions showed that they could reveal essential information about the magma just before an eruption.
It gives information about the chemical composition of the magma and about its consistency - how runny or sticky it is. The inclusions also provided details of the depths from which the magma emerged.
These details are hugely important because they give potential insights into the kind of eruption an active volcano might deliver, Dr Blundy said. "The more sticky the magma is, the slower the eruption. The more runny it is, the more likelihood there is for a violent eruption."
Magma consistency is related to how quickly it begins to form crystals once released from the volcano. It remains fluid while under high pressures, but when released during an eruption it quickly begins to crystallise, he explained.
Unexpectedly, the two Bristol scientists established that the magma gives off significant heat as these crystals form, pushing up temperatures by as much as 100 degrees, in a process known as the "latent heat of crystallisation". This can help keep magma more fluid and support self-sustaining violent eruptions, he said.
These are also helped by a rapid loss of the water trapped in the magma which percolates upwards to escape, like the fizz from a shaken bottle of champagne.
Their work provides insights about what takes place underneath the volcano, information that now needs to be matched up with the extensive monitoring data being collected around Mount St Helens and Shiveluch.
"Developing links between what goes on underground and what happens on the surface is like the holy grail of volcanology," Dr Blundy said.
He is now shifting his attention to the Colima volcano in Jalisco state, Mexico. It is similar to Mount St Helens and could be the next major volcano to blow its top.
