Between a Rock and a Hard Place


Alumnus profile #6 – Dr Sam Engwell

DSC_0500Dr Sam Engwell

Marie Curie Early Stage Researcher, INGV

PhD title “Dynamics and Deposits of Large Explosive Eruptions”



1) The Twitter Challenge: Describe your PhD in 140 characters

Investigation of eruption processes during supereruptions by analysis of deposits in deep-sea sediments.

Deep sea core

Deposits from the Campanian Ignimbrite eruption can be found over 1000km away from the eruption source in deep sea cores. Photo credit: Sam Engwell

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Science snap (#31): Mammatus clouds

After all the thunderous weather this weekend and being British, I thought I’d do a weather themed science snap. Don’t bolt yet; it’s a volcanic-weather themed!

Volcanic mammatus clouds forming after the eruption at Mount St. Helens. Copyright: Douglass Miller

Volcanic mammatus clouds forming after the eruption at Mount St. Helens. Copyright: Douglass Miller

This is a picture of mammatus clouds following the eruption of Mount St. Helens in 1980. These clouds are pretty rare, unusual and distinctive. Formally, the Glossary of Meteorology defines mammatus clouds as “hanging protuberances, like pouches, on the undersurface of a cloud”. The definition is aptly descriptive, but in essence mammatus are a series of bulges at the base of clouds, often under large thunderous cumulonimbus clouds. There are many different types of mammatus clouds, each with distinct properties and occurring under various cloud types, and mammatus in volcanic clouds is just one subcategory. There are relatively few documented occurrences of Mammatus under volcanic clouds. Apart from Mount St. Helen’s, they’ve been observed at during the eruption of Mount St. Augustine on 27–31 March 1986 and Mount Redoubt on 21 April 1990. No generally accepted formation for these mechanism exists, however it is clear that a sharp temperature gradient and a wind shear across the cloud-air boundary is needed to create these clouds. Did anyone spot Mammatus clouds in the UK this weekend?

Life and death, and money

Mel Auker is an Earth Sciences PhD student in the School of Earth Sciences at the University of Bristol. A mathematician by trade, Mel’s PhD uses numerical approaches to better understand past, present, and future global volcanic hazard and risk.

The recent tragedy at Sinabung volcano, Indonesia, bought some interesting thoughts to light amongst some members of the volcanology group at Bristol. There were comments regarding the decision by the authorities to allow people to return to their homes (you can see James Hickey’s perspective here). In an ideal world, I’m sure we are all agreed that the risks of volcanoes and their eruptions would be fully mitigated, and fatalities and financial losses would be zero.

Sadly, there is no such ideal. The reality is one of limited resources and a need to balance the benefits and costs of risk reduction to society. Personally, I find the concept of attaching a value to a life a difficult one. But policy makers calculate the Value of a Statistical Life (VSL) in order to make rational risk-reduction decisions at the societal level. The VSL is defined as the value an individual places on a marginal change in their likelihood of death, i.e. the price an individual is willing to pay for a small decrease in the likelihood of their death. In theory, the VSL could be calculated as follows:

“Suppose each person in a sample of 100,000 people were asked how much he or she would be willing to pay for a reduction in their individual risk of dying of 1 in 100,000, or 0.001%, over the next year. Since this reduction in risk would mean that we would expect one fewer death among the sample of 100,000 people over the next year on average, this is sometimes described as “one statistical life saved.” Now suppose that the average response to this hypothetical question was $100. Then the total dollar amount that the group would be willing to pay to save one statistical life in a year would be $100 per person × 100,000 people, or $10 million. This is what is meant by the value of a statistical life.” US Environmental Protection Agency

The price of a life

What price on a life? Image credit: Mel Auker

In practice, VSL calculations are often based on the payments people receive for risks they voluntarily take in their day-to-day life, by examining the wages paid in different jobs. After controlling for all the other factors that may affect wages (such as location and skill level), the remaining wage variation can be attributed to compensation for the risk of death. This value can be used in the same way as in the example above to calculate the VSL. Another similar method involves comparing the price people are willing to pay for goods of differing safety standards, such as cars.

The outcomes of VSL calculations are varied, but Miller (2000)1 presents a review of 39 US and 7 UK studies and produces data-based estimates of $3.472m and $2.281m in 1995 US dollars for these countries, respectively. There are insufficient data for Indonesia, but using a series of assumptions and proxy values, Miller estimates a Indonesian VSL in 1995 US dollars of only $0.16m.

These values are obviously approximate and somewhat outdated, but nevertheless provide rather haunting food for thought when considering how much should be invested in risk reduction at the societal level across the world.

Whilst the VSL concept can seem alien and cold, the events at Sinabung and the circumstances of the deaths – people had returned to check on their homes and possessions – perhaps suggest that those facing such risky situations may subconsciously perform a VSL-type calculation. For those who stand to lose everything in an eruption, it seems the line between life or livelihood is incredibly blurred.

[1] Miller, TR (2000) Variation between Countries in VSL. Journal of Transport Economics and Policy, Vol 34 No.2

Science Snap (10): The impact of eruptions

Mel Auker brings us our Science Snap this week…

Many people are aware of the May 1980 eruption of Mount St. Helens in Washington State, USA. Common photographs of the huge VEI 5 eruption show the large, billowing eruptive column rising into the stratosphere.

Less iconic are images of the destruction left behind, demonstrating the after-effects of the eruption. The US president at the time, Jimmy Carter, flew over St. Helens soon after and said the area looked “more desolate than a moonscape.” Now, more than 30 years on, the landscape still displays reminders of the awesome power of nature. Below are a selection of photographs taken in August 2011.

From top left, clockwise: 1. “Miner’s Car”, the remains of a car situated approximately 15 km from the volcano at the time of the eruption; 2. Trees flattened by the debris flow; 3. Tree trunks in Spirit Lake, approximately 8 km north of the volcano; 4. Hummocky avalance deposits. Credit: Melanie Auker

The top left photograph is of “Miner’s Car“, which has been left in place as a monument approximately 15 km NE of St. Helens. The heat of the eruption burnt all the exposed paint off the car, though the bumper (at the right of the image) is still largely undamaged. The top right photograph shows large trees flattened by the eruption, mantling the topography and identifying the direction of flow.

The bottom left photograph shows the huge number of tree trunks present in Spirit Lake, approximately 8 km north of St. Helens. As well as flattening trees, the eruption tore thousands from the ground which were deposited in the lake. The volume of material emplaced in the lake has reduced its surface elevation by over 60 m. The bottom right photograph depicts the rounded mounds (hummocks) that form part of the debris avalanche deposit to the north of the volcano. They are formed of relatively intact rocks that once formed the volcano’s summit.