Lava flows, streams of molten rock erupting from volcanoes, represent a powerful natural hazard. These flows can inundate vast areas, destroying homes, infrastructure, and agricultural land. Their extreme heat, ranging from approximately 700°C to 1,200°C, can ignite and bury everything it encounters. Communities near active volcanic regions often face this threat, prompting efforts to alter or stop the progression of lava flows.
Understanding Lava Flow Behavior
The characteristics of lava significantly influence its movement and potential for redirection. Two common types of basaltic lava are pahoehoe and ‘a’ā, distinguished by their surface textures and flow properties. Pahoehoe lava is smooth, ropy, and flows more fluidly due to lower viscosity. It can travel quickly, covering large areas rapidly.
In contrast, ‘a’ā lava has a rough, rubbly, and jagged surface, making it thicker and more viscous. This type of lava moves slower but can be more destructive as its blocky nature crushes or buries structures. The speed and distance a lava flow travels are also affected by its temperature, the steepness of the ground, and whether it flows as a broad sheet, through a confined channel, or within a lava tube. Hotter lava flows are less viscous and more fluid, allowing them to advance more easily.
Techniques for Lava Diversion
Methods to divert lava flows include constructing physical barriers, such as berms, dikes, or walls, to redirect the flow away from populated areas or infrastructure. These structures aim to create artificial channels or impoundments, forcing the lava to accumulate or change direction. The effectiveness of these barriers depends on their height, strength, and the volume and pressure of the advancing lava.
Another technique involves cooling the lava with water, by hosing large volumes of water onto the flow front or using aerial drops. Rapid cooling increases the lava’s viscosity, causing it to slow down and solidify, potentially forming a barrier against further advancement. It accelerates the natural cooling process, transforming the molten rock into a solid mass.
A more aggressive strategy uses explosives, such as bombing or blasting, to alter the flow path. This involves creating new channels or collapsing existing ones to divert the lava into less hazardous areas. The underlying principle is to modify the topography in front of the flow, guiding it along a different route or breaking up the flow front to reduce its momentum.
Complications of Diversion Efforts
Diversion techniques face significant difficulties in implementation. The scale and speed of many lava flows present logistical challenges, requiring immense resources and rapid deployment. Lava’s unpredictable nature, including sudden changes in flow direction or breakout points, further complicates efforts. This unpredictability makes it difficult to ascertain where to build defenses or apply cooling measures with certainty.
The costs associated with large-scale diversion projects are high, encompassing equipment, personnel, and materials. Environmental impacts also pose significant concerns, as diverting lava from one area often means redirecting it to another, potentially impacting new communities or pristine ecosystems. The interaction of lava with water can also lead to steam explosions, which can be dangerous and spread molten spatter.
Ethical dilemmas emerge, particularly when diversion efforts might shift the threat from one community to another. Decisions must weigh the protection of certain areas against the potential destruction of others, leading to complex societal and political considerations. The high heat and pressure of lava can also render many conventional construction materials ineffective, posing a challenge for creating durable and resistant barriers.
Notable Diversion Cases
Historical attempts to divert lava flows highlight challenges and outcomes. During the 1973 Eldfell eruption on Heimaey, Iceland, an effort involved continuously spraying seawater onto advancing lava flows. This cooling operation helped solidify the lava, slowing its progress and preventing the closure of the harbor, which was important for the island’s economy.
In Hawaii, attempts have been made to manage Mauna Loa lava flows, including the construction of earthen barriers or the use of explosives. For instance, in 1935 and 1942, military bombing was used to divert flows, with mixed and debated success. The goal was to break up the lava tubes or create new paths, though the efficacy of these actions remains a subject of scientific discussion.
Mount Etna in Italy has also seen diversion efforts, including the construction of earth barriers and the use of explosives to create new channels. In 1983, an operation involved building an earth barrier and then blasting a channel to redirect a flow threatening a populated area. While the lava did eventually flow into the constructed channel, success was attributed to a combination of human intervention and the natural slowing of the flow.