Decades of poorly researched Hollywood movies have conditioned us to think of molten lava flowing like water, pouring from a volcano in red-hot torrents to overwhelm people and property alike.
Fortunately for the half-a-billion people living around the world’s 1 500 active volcanoes, this perception is seriously flawed. Most are simply too sticky to move in this way.
The lava pumping out of Sicily’s Mount Etna, for example, has a viscous consistency that makes its movement sluggish.
The viscosity of a lava flow increases further as it cools, until eventually it becomes solid rock. This means that building barriers to protect property or divert flows is far more problematical than constructing dykes or walls to hold back flood waters.
But this has not stopped people attempting to fight back and no more so than at Mount Etna, where there is a long history of battling lava flows.
The earliest attempts are recorded from the 1669 eruption.
Now lava is once again posing a problem, threatening the hamlet of Nicolosi-nord high on the southern flanks of the volcano, and scientists and engineers are struggling to protect the famous Rifugio Sapienza, home from home to countless generations of enthusiastic volcanologists.
This part of the volcano is one of the most active, with magma stored below the summit craters pushing outward to burst through the flanks just a few kilometres above the tourist centre. In 1983 lava fed in this way threatened to inundate a number of towns and villages on the southern flank, leading to the first serious attempt for more than 300 years to modify the flow.
Earth barriers were rapidly bulldozed into position above the Sapienza. But lava cools and solidifies against a barrier, allowing further lava to pile up, eventually overtopping the obstruction. Lava soon surrounded the refuge and crashed through the back wall into the kitchen. Amazingly, the flow then stopped, saving the rest of the building.
Lower down, however, flows crept closer to some of the major towns.
Scientists and engineers sanctioned an unprecedented attempt to use explosives to alter the course of the eruption. By blasting through the solidified margin of the flow high up on the volcano, they generated a secondary stream of lava that short-circuited the supply to the threatening active flow lower down. Shortly afterwards, it ground to a halt, but it seems that this reflected a drop in the rate of lava production rather than the attempts of the explosive experts.
Nevertheless, the episode defined a sea change in the way volcanologists and civil protection officials viewed eruptions of Etna.
Etna is one of the most active volcanoes and only rarely will a year pass without new magma breaching the surface. In 1991 another opportunity arose for scientists and engineers to hone their diversion skills. Lava began to pour from fissures high on the eastern flank, draining into the giant, cliff-bounded amphitheatre known as the Valle del Bove.
Having spread out across the amphitheatre floor, the lava threatened to dribble out of its open eastern end and close rapidly on the village of Zafferana. A huge holding barrier of earth and rock, tens of metres high and more than 400m long, was built across the open end of the Valle del Bove, which held back the lava for several months.
In early 1992, however, the flows eventually overtopped the artificial dam and sped down a narrow valley towards Zafferana. A series of earth barriers was constructed across the valley to try to slow down the flow, but to no avail.
At the eruption site, volcanologists decided on another tack, attempting to divert lava from the main channel, thus cutting off the supply of fresh magma to the flow nearest Zafferana.
By blasting through the wall of the primary feeder channel the lava was encouraged to follow a new path, on top of the existing flow rather than feeding it. Movement of the front close to the town ceased, and the eruption ended early the following year.
It was probably the most successful attempt at changing the course of a volcanic eruption, but there remain doubts about whether the flow would have reached Zafferana anyway. Some feel the front had probably reached its furthest extent when it ground to a halt on the outskirts.
Nevertheless, enormous experience has been gained. As I write this, two earth barriers continue to keep lava from the door of the Rifugio Sapienza. Of greater concern is the fact that it is now more than 70 years since a major town was destroyed by lava from Etna — Mascali was obliterated in 1928. It is only a matter of time before another community faces similar extinction.
The big worry is that an eruption much lower down, with a much higher rate of effusion, will not provide enough time for diversionary measures. Only when such a scenario arises will we discover if we can truly tame one of nature’s most potent destroyers, or if Vulcan is still the boss. — Â