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Earth's hottest place

How to build a 3D volcano: Dougal Jerram and Steve Smith take laser scanning to the very edge, and build the ultimate 3D volcano…

Geoscientist 20.02 February 2010

The East African rift and the Danakil desert in the Afar region of Ethiopia <fig 1> conjure up images of grand scenery, melting sunsets and the mysteries of the Afar tribal warriors. This is a truly special place where the mountains meet the sea, and rifting of two tectonic plates drives the birth of a new ocean. It is home to countless volcanoes, faults and fissures as well as a striking variety of animals and humans who have adapted over time to the notoriously harsh environment. Our aim during a three-week trip at the end of 2007 was to visit active fissures and volcanoes as part of a popular TV programme, and to capture these remarkable features using the latest 3D laser scanning technology - a virtual volcano hunt.

Scanning an outcrop involves the scanner measuring millions of xyz points and colouring them with their true RGB colour from a digital photo. A computer is used to stitch several scans together and further process data. A 3D laser scanner provides the opportunity to create true 'virtual' outcrops. By firing millions of laser-points towards the real outcrop, the scanner is able to record the position of the objects in front of it. In essence, it captures a 3D photograph, from which we can build high resolution geological models at a variety of scales. The scanner creates a 'point cloud' - a collection of millions of points defining the 3D environment <fig 2>, and then uses digital images taken using a conventional camera, specifically calibrated for the scanner, to colour the point cloud, ultimately generating a virtual 3D picture at millimetre resolution.

Journey to Afar

Arriving in the hottest place on Earth is no mean feat. A three-day camel ride from the mountains of the Ethiopian Plateau to a barren desert some 100m below sea level marks just the first leg of the journey. There, in the Danakil Depression, lie some of the most extensive salt flats on Earth, a precious commodity that has been mined and traded for thousands of years. With camels loaded with over 80kg of scanning equipment, we then headed off in search of the main geological highlights of this expedition.

Our first target was the Dabbahu fissure, a steaming gap in the Earth’s crust. We would then set our sights on the final goal, the ascent and then descent into Erta Ale, one the oldest and most active lava lakes in the world.

The Dabbahu fissure is a gaping wound in the Earth created virtually overnight in September 2005 by rifting and a volcanic eruption. As we approached the edge of the fissure we were presented with a sight straight from a Hollywood movie. The scale was unimaginable, and you really felt that the Earth could just tear itself apart. We managed three scans around the fissure’s edge before being beaten back by noxious gases.

Our hero descends into the abyss

Erta Ale – hell’s gate or geological heaven?

Erta Ale is one of the oldest and most active known lava lakes, and gazing down into its fiery cauldron one can imagine why in Afar legend it is known as the 'Gateway to Hell'. After another long trek we found ourselves camping at the edge of the summit caldera, which hosts the north and south pit craters. The south crater contains the active, bubbling lava lake, glowing red at night and constantly turning over like boiling porridge. Our objective was to capture the first 3D laser scan from within an active volcano. We began to position scans around the caldera and along the rim of the crater <fig. 4>. The final scan was the key to unlocking Erta Ale's secrets and bringing the 3D model to life, but it would be a daring one - involving an abseil into the crater itself.

After three weeks of dust and camel spit, as well as wonder and amazement at the Danakil desert and the humour and resilience of the Afar people, we were at last dangling over the edge of a live volcano. It is almost impossible to convey the effect of that mix of adrenaline (during the abseil) and the eerie calm that prevailed as we touched down on the crater floor. It was the culmination of a journey that had tested the limits of our capabilities, united strangers who would leave as friends, and provided so many wonderful experiences.

View into Erta Ale - final model

The final scan

To get the full 3D crater of Erta Ale we needed to scan around the crater from the very rim (roped up for safety), and finally we would need to get both ourselves and 80kg of kit down into the lower ledge of the volcano fort that vital all-important final scan required for the complete 3D model.

The final 3D models represent the first ever laser scans of Dabahu fissure and of live active lava lake, Erta Ale. These 3D models provide snapshots of exactly what these features were like at the time, and form the basis from which our future understanding of how these structures develop in years to come.