How Can Communities Redirect Dangerous Lava?

TL;DR

Communities can sometimes redirect or halt lava by cooling it with huge volumes of water or constructing large earthen barriers, while bombing lava has not proved effective. Because lava generally moves slower than 1 kilometer per hour and becomes solid after cooling to roughly 600° Celsius, people may have time to evacuate and deploy defenses.

Transcript

Late at night on December 18th, 2023, the Icelandic citizens of Grindavik experienced their worst nightmare. After weeks of earthquake-filled suspense, a volcanic fissure opened four kilometers northeast of town and began spewing lava fountains 100 meters tall. Luckily, the molten rock flowed elsewhere, narrowly avoiding the small fishing town. But... Read More

Key Insights

• Lava is molten rock that is called magma underground and lava after it reaches Earth’s surface. It can reach roughly 1,200° Celsius, causing it to ignite or melt most things in its path while radiating intense heat across potentially large areas.
• Lava flows are difficult to stop because molten rock is as heavy and dense as the solid rocks from which it comes. Its immense heat and mass make an advancing flow almost unstoppable, especially when an ongoing eruption continues supplying fresh lava.
• Lava generally advances slower than 1 kilometer per hour, giving threatened communities time to evacuate and organize defensive measures. It can take decades to cool completely, but it becomes solid and stationary after reaching roughly 600° Celsius, often within a few hours without continued fueling.
• Bombing lava is not considered a dependable control strategy. Although 20 bombs were dropped on a Mauna Loa flow threatening Hilo in 1935, most volcanologists believe the flow stopping six days later was coincidental because displaced liquid lava could refill bomb craters.
• Cooling lava with water can stop an advancing section, but lava’s low heat conductivity requires enormous volumes. During the 1973 Eldfell eruption, Iceland pumped 6 million cubic meters of seawater onto the flow, enough to fill 2,400 Olympic-sized swimming pools.
• The Heimaey cooling operation protected the harbor through sustained coordination. At the campaign’s peak during the six-month eruption, 75 people worked around the clock in shifts and sprayed each actively advancing area for roughly a full day to halt its movement.
• Earthen barriers can divert lava away from populated areas and are commonly built from sand, dirt, or volcanic gravel. During Mount Etna’s 1983 eruption, workers used 750,000 cubic meters of material, equivalent to 25,000 truckloads, to construct four large barriers.
• Grindavik’s 25-meter-high barriers successfully diverted lava from multiple eruptions after the 2023 event. Because diverted lava raised the surrounding ground level, workers had to elevate the barriers between eruptions, demonstrating that defenses may require repeated adaptation as conditions change.

Questions & Answers

Q: How can communities redirect a dangerous lava flow?

Communities can construct large barriers from sand, dirt, or volcanic gravel to steer lava away from populated areas. Mount Etna workers used 750,000 cubic meters of material to create four barriers in 1983. Grindavik later built barriers 25 meters high that redirected flows from multiple eruptions, although workers had to raise them as accumulated lava elevated the ground.

Q: Can water cool lava enough to stop it flowing?

Water can stop advancing lava when it is applied in enormous quantities for sustained periods. During the 1973 Eldfell eruption, Iceland pumped 6 million cubic meters of seawater onto the flow. At the operation’s peak, 75 people worked around the clock and sprayed each actively advancing section for roughly a full day, ultimately helping save Heimaey Harbor.

Q: Why does cooling lava require so much water?

Cooling lava requires enormous quantities of water because lava has low heat conductivity and can reach roughly 1,200° Celsius. The scale was demonstrated at Eldfell, where 6 million cubic meters of seawater, enough for 2,400 Olympic-sized swimming pools, were pumped onto the flow. The method succeeded but depends on access to an exceptionally large water supply.

Q: Does bombing a lava flow stop an eruption?

Bombing has not been shown to stop lava reliably. In 1935, the US Army Air Corps dropped 20 bombs on lava from Mauna Loa that threatened Hilo. The flow stopped six days afterward, but most volcanologists consider the timing coincidental. Because lava behaves like a liquid, bombs may only displace it briefly before it refills the resulting craters.

Q: How quickly does lava move toward populated areas?

Lava generally flows at less than 1 kilometer per hour. That relatively slow pace can provide time for people to evacuate and for authorities to organize defensive responses. Speed alone does not make lava easy to control, however, because the molten rock is extremely hot, heavy, and dense, and an ongoing eruption may continually replenish the advancing flow.

Q: At what temperature does lava become solid and stop?

Lava becomes solid and stationary after cooling to roughly 600° Celsius, even though complete cooling can take decades. This initial solidification often occurs naturally within a few hours when an eruption is not continuing to feed the flow. Fresh lava from an active eruption can prolong movement and make defensive operations more difficult to complete.

Q: What materials are used to build lava barriers?

Lava barriers are typically constructed from readily available earthen materials such as sand, dirt, or volcanic gravel. Their purpose is to redirect a flow rather than cool it. The required scale can be immense: workers confronting Mount Etna in 1983 used 750,000 cubic meters of material, equal to approximately 25,000 truckloads, to erect four barriers.

Q: Why must lava barriers sometimes be raised repeatedly?

Barriers may need to be raised because redirected lava accumulates and increases the surrounding ground level. Grindavik’s 25-meter-high barriers successfully diverted flows from multiple eruptions, but workers elevated them between events as the terrain changed. The approach allows defenses to be strengthened between flows, provided authorities can anticipate likely routes and continue adapting the structures.

Summary & Key Takeaways

• Lava can reach roughly 1,200° Celsius, ignite or melt most materials, and resist intervention because it is as dense as its source rock. However, flows generally travel slower than 1 kilometer per hour and become stationary after cooling to roughly 600° Celsius, creating time for evacuation and carefully organized responses.

• Bombing lava is considered unreliable. During Mauna Loa’s 1935 eruption, 20 bombs were dropped to protect Hilo, and the flow stopped six days later. Most volcanologists regard that timing as coincidental because liquid lava would probably be displaced temporarily, refill the resulting craters, and continue moving rather than remain contained.

• Water cooling and earthen barriers have produced stronger results under suitable conditions. Seawater pumping helped protect Heimaey Harbor in 1973, while barriers redirected flows at Mount Etna and Grindavik. Both approaches demand extensive resources, planning, labor, and repeated adjustments based on the eruption’s location, duration, and continuing lava supply.