Lava from the Kilauea volcano in Hawaii threatened to reach communities on the Big Island and authorities declared a state of emergency. But is there an effective way to stop the lava and save the houses in its path?
Sicilians have always been threatened by Mount Etna, the volcano located in the northeast of the Italian island.
In 1669, the residents of the town of Catania faced the destructive advance of the lava «armed with picks and shovels and protecting themselves from the heat with wet sheepskins», according to the historical account, and opened a breach to cut off its path.
But the inhabitants of the neighboring town of Paterno did not like the idea, because they believed that the diversion of the burning lava was aimed directly at their own community.
So he decided to seal the ditch and the volcanic fluid continued its course towards Catania and destroyed a large part of the town.
That was the modern start of what Shannon Nawotniak, a geologist at Idaho State University, calls a «spectacularly poor success rate» in curbing volcanic impetuousness.
At temperatures around 1,000ºC, molten volcanic material destroys everything it touches and its path is difficult to predict.
The ability to impede or redirect the flow of lava depends on location, resources, and luck.
Here are four strategies that didn’t fare too badly:
1 – Bomb
Before he became a general in World War II, George S. Patton framed a very different military campaign: the bombing of Hawaii’s Mauna Loa volcano, the largest on Earth, when it erupted in 1935.
When lava began flowing at a rate of 1 mile per day toward the city of Hilo, then-director of the Hawaiian Volcano Observatory, Thomas Jaggar, suggested bombarding the volcanic tubes.
Lava tubes are formed when the outer layer cools and holds, insulating and facilitating the flow of molten rock within. These tubes make the lava move faster.
In theory, the bombs were going to destroy the volcanic tubes and make more lava cool on contact with the air and therefore its flow would be slower.
But in practice, although the bombs created craters in parts of the tubes, they soon filled with lava again.
The town of Hilo was only saved because the volcano quenched its eruption.
Subsequent tests by the US Air Force suggested that larger, more modern bombs might be more effective if targeted at the most vulnerable sections of lava channels.
2 – Cool with water
One of the most successful attempts occurred in the 1970s on the island of Haimey, in Iceland.
Lava from the Eldfell volcano threatened the village of Vestmannaeyjar and the port.
For almost five months in 1973, the inhabitants threw icy sea water with fire trucks at the advancing burning material.
When the water reached the hot rock, it turned to steam and allowed the heat of the lava to dissipate.
A fifth of the town was destroyed before larger hydrants were brought in, but much of the lava flow was slowed and diverted and the harbor was saved.
As Nawotniak explains, in this case the conditions were right: Eldfell’s lava was particularly slow and there was an inexhaustible source of water nearby.
3 – Build a barrier
Back on Mount Etna, an eruption in March 1983 threatened to level three villages.
Rock and ash barriers were then built to try to divert the lava.
«They were trying to slow it down and steer it down the mountain,» Nawotniak says in conversation with the BBC.
One of the first barriers, 18m high and 10m wide, was exceeded by the volcanic flow, but a second barrier prevented the lava from advancing west.
Two other large walls kept the molten rock from reaching the main tourist area of Etna, on the eastern side of the valley.
The lava passed a few meters from buildings, and one of the barriers, known as Sapienza, grew two meters from the addition of lava.
4 – Add concrete
Almost 10 years later, Etna erupted again and the Italian authorities used the lesson from the last time to save the town of Zafferana.
In addition to the barriers, workers created an artificial trench to trap lava coming from a breach made with explosives.
That only moved part of the flow away, so concrete blocks were added to the rest of the lava and thus diverted its path.
However, according to the United States Geological Survey (USGS), the diversions of Iceland and Etna «were unsuccessful if eruptions continued.»
«You have to live in a rich country with a lot to lose to consider lava diversion,» says Nawtniak, noting the volume of volcanic eruptions and their potential costs.
«You can buy some time until the volcano stops on its own,» he adds.
According to the expert, geologists see the diversion of lava as a losing battle.
It would be better, he says, to focus on improving the prediction of eruptions.