Scientists & Instruments

Have you ever wondered what a lava dome looks like? 

In October 1971 La Soufriére St Vincent entered a period of unrest. Over the coming weeks, the volcano entered an eruptive phase with a lava dome growing in the crater - visible above the level of the crater lake.

Take a look at the photos below, does the dome look like you would have imagined? 

The images you see from 1971 are mostly black and white because colour film was expensive, but in the colour photos taken in 1977 you can see that the lava dome is black. When people imagine lava, they often think of glowing reds and oranges, but when lava erupts the outside cools more quickly than the interior, so even when it was first erupted, much of the lava dome would've appeared black.

Sometimes though, when a lava dome is growing, cracks in the surface expose some of the red hot interior and the heat from the lava can give off a red-orange glow. 

Is the dome dangerous? 

The emergence of a lava dome caused concern amongst the local population and the government called in scientists from the Caribbean, UK and US to help assess the risk to the public. They had many questions...

How big would the lava dome get? Was this a sign of a more explosive eruption to come? Should people evacuate?

Scientists hoped to help answer some of these questions by making careful observations and measurements using a variety of instruments. 

More sophisticated instruments can be more sensitive to minute changes that give us new insights into sub-surface processes. However, we must also be careful to ensure these instruments are being applied in a way that is useful and that the data can be reliably interpreted.

A volcanic system is like a jigsaw puzzle, we use different instruments to see separate pieces of that puzzle, then find a way to put them together. 

Shaking - Seismometers:

Seismometers detect the tiny (and sometimes not so tiny) movements of the earth. When magma moves closer to the surface at volcanoes it fractures the rock causing small earthquakes. These can be detected by seismometers and provide an early warning of potential increases in activity. 

Back in 1971, the initial scarcity of seismometers meant any signals that may have shown magma migration prior to the dome breaching the lake surface (late October - November) were not captured and scientists had to rely on visual observations.

Once a wider network was installed, scientists gave regular reports of changes in seismic activity beneath the volcano. As volcanic tremor is often associated with the movement of magma, Dr John Tomblin was confident that any seismic activity would warn of any imminent explosive event at least 24 hours in advance. 

Heat - Infra-red Camera:

Influx of hot new magma into a volcanic system typically raises the temperature of the local environment. Before the dome breached the surface of the crater lake, scientists were unsure whether the elevated temperatures recorded were associated with fresh lava at the surface, or just the migration of hot magma in the shallow sub-surface. 

When the USGS arrived with their infra-red camera, decision-makers hoped this would provide significant insights into the volcanic system and provide clarity on what to expect in terms of future activity. 

"American seismologists...have infra red aerial photography...enables them to predict with astonishing accuracy the likelihood, likely time and the likely extent of an eruption"

Data from the infra-red camera at first appeared to indicate an imminent threat to populations in and around the Larakai and Rabacca valleys due to apparent "hot water leakage" from the crater. When hot magma comes into contact with water under pressurised conditions (e.g., in the subsurface) it can rapidly vaporise and expand, violently blasting magma and rocks apart in sudden, powerful explosions. Fears that this type of activity could be indicated by the infra-red data are thought to have influenced the decision to evacuate northern parts of the island. 

However, this interpretation was later deemed to be false causing some consternation among decision-makers in St Vincent and the UK. 

Scientists have to take care to effectively explain the uses and limitations of the data they can provide and the instruments they use to get it. Over-reliance (by scientists and/or decision makers) on a single dataset can lead us to focus on a single puzzle-piece rather than the whole picture.