This month’s picturing science image, from University Research Fellow Dr Hugh Tuffen, is just four millimeters across. It shows the remarkable microscopic textures within obsidian, or volcanic glass, formed in an Icelandic eruption twenty-five thousand years ago. Obsidian forms from cooling of magma with a high silica content, which makes it very viscous.

This high viscosity also means that crystal growth is sluggish and the few crystals that do form include rounded masses called spherulites that are rich in the mineral cristobalite, a mineral hazardous to human health. Some of these enigmatic crystals are captured in the image, along with dark bands picked out by micron-scale crystals. These bands record how the magma flowed and folded around a perfectly circular bubble of trapped gas.

Dr Tuffen is a volcanologist who investigates the processes that control hazardous eruptions. He is currently using a combination of field studies on active volcanoes and experimental approaches in the lab to address how gases escape from magma and how crystals such as spherulites grow. He was one of the lucky few to witness an obsidian lava flow when he visited Puyehue-Cordon Caulle volcano in Chile and the second image here shows the setting sun lighting up the plume as Puyehue-Cordon Caulle erupts.

During his 10 day trip in January 2012 he collected samples, videos and images, providing a rich resource for future research. If being there to witness the eruption wasn’t exciting enough, he also shot a film of the expedition that was featured in the BBC Volcano Live series. The clip can be found here and is definitely worth a watch.

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