The fourth eruption since December has been underway in the Reykjanes peninsula near the town of Grindavík, Iceland. Prior to this event defensive walls were built north of the town, with planned dimensions of two kilometres long and four metres high. For now, they have worked. As long as the fissures open on that side of that wall, this is a preliminary success. So why don’t we always do this?
Janine Krippner
Lava is incredibly heavy and dense. You can’t just throw things in front of lava and expect them to hold the enormous pressures and energies involved. Some lava flows are also metres to several tens of metres thick. A four metre high wall would not do much against a 10 metre thick lava flow. So, there is the practical considerations of would it even work? The La Palma lava flow field reached around 70 metre thick. These scales are much larger than what we can construct, especially during a crisis. The physical properties of the lava itself must be taken into consideration. The current Icelandic lava flows are relatively thin and fluid, thankfully.
Lava flows are driven by how much is coming out of the vent and the physical properties of the lava itself, and this changes with time. This incredibly dense fluid can also form lava tubes or travel down into cracks, making it difficult to see where it is flowing. Often simply building a wall is not going to do much at all, but sometimes it really does help. The location is also important. If a populated area is close to a vent or the lava is flowing at high speeds, little can be done with a short timeframe.
There was an enormous effort during Heimaey eruption at Vestmannaeyjar, Iceland, in 1973 to cool lava flows with water to save the important seaport on the island. Five months of effort, 43 water pumps, access to sea water, and the harbour was saved. Over 400 homes were still destroyed, and more were damaged.
Attempts to bomb lava flows to change their course have been made in Hawaii and Etna with mixed results. There was success at Etna in 1983 when bombs were strategically combined with digging large trenches and building barriers, but it is noted that a lava flow has to be confined inside a well-developed channel for such an attempt to possibly work. Lava flows are often not confined, instead they spread out like sheets, especially early on, or several flows may be active and change throughout the eruption.
If you have an eruption in a populated area there a critical ethical question – where will the lava go? Are you going to save your building but direct it towards other homes that otherwise would have been untouched? If you have a densely populated area this is going to be a major issue. There are also cultural considerations. In Hawaii there is a respect for the Goddess Pele and the local relationship with the volcanic landscape, where it is inappropriate to interfere.
This is a great example of where volcanology (understanding the lava flow and how the eruption might change), other specialties (engineering) and societal aspects (population, economic, and cultural) must come together to focus on how to respond to volcanic events. Unfortunately, evacuate, wait, and hope is the only course of action much of the time.
