Wednesday, November 6, 2013

Pouring Lava on Ice: for Science!

Eruption plume above Eyjafjallajokull volcano, Iceland, April 17, 2010.
 In the foreground is the meltwater floodpath from eruption-induced ice melting.
Photo credit: Eyjoful Magnusson, University of Iceland. Source


In 1973, a new volcano erupted on the island of Heimaey, part of the Westman Islands off the southern coast of Iceland, and threatened the very existence of the inhabitants and their way of life as they knew it. The main town of the island, Vestmannaeyjar, became partially inundated with lava but the inhabitants knew they would be able to rebuild their town. However, the lava was also advancing toward the only harbor on the island, threatening to seal off the harbor and destroy this fishing community’s livelihood as well as one of Iceland’s main fishing port. The Icelanders came up with a novel plan to desperately attempt to save the town. The idea? Throw enough cold water on the lava in hopes of creating a solidified lava wall to divert the rest of the lava away from the harbor. It took two months of water pumping and the entire arsenal of pumping ships from the area (high-capacity pumps were even brought in from the US) but the harbor was eventually saved. This event is one rare case of a “successful” fight against an advancing lava flow; however, half of the town was still destroyed and a similar event could occur at any time.
Lava flows are not the only volcanic threat to life and infrastructure. Lava flowing over ice or snow can induce rapid melting, leading to an unexpected debris filled flood event. Volcanic eruptions are dangerous and need to be quantitatively measured in order to better understand the hazards associated with them. Specifically, understanding the interactions between lava and ice is critical in developing hazard assessments. We care about the interactions between lava and ice because of the rapid melting involved and the increased risk for flash flooding and debris flow events, such as lahars and jokulhlaups. However, because volcanoes are often in difficult to reach places and an eruption involving lava and ice is inherently dangerous, it is difficult to observe the lava/ice interactions closely. Moreover, a lava flow traveling over ice may melt sufficiently through it and begin flowing underneath and/or through the ice, where it is no longer observable from the surface.
In an attempt to address these observational and measurement difficulties, a group of scientists out of Dickinson College, Pennsylvania, in collaboration with Syracuse University, New York, have created a way to observe and measure the interactions of lava with ice and snow (figure 1). In short, their experiment is to pour basaltic lava onto layers of ice or snow in a controlled setting to observe and measure the interaction. Multiple experiments were performed using blocks of ice, shaved ice, and sand (to simulate an ash covered ice surface).


Images of the experimental lava flows advancing over ice and snow. The top image is lava flowing over an ice bed 12 cm thick (the width of the flow is 15 cm). The second image is lava flowing over snow 12 cm thick (the width of the flow is 20 cm). Images are from the original article. 

Experiments reproduced two end-member melting behaviors consistent with field observations: (1) flows that melted quickly through ice and (2) flows with slow initial melting. In experiments without a sand layer, lava advance was inhibited due to it quickly melting through and sinking into the ice. Eventually the lava melted through the ice to the container bottom and again flowed downslope along the container-ice boundary. These experiments show the ability of lava to exploit these crevasses to flow downward and through ice. By controlling the starting geometries for ice-lava boundaries we can test different hypotheses for ice confinement of lava flows.
One of the more interesting observations is that during some experiments the lava would appear to skate across the ice; this is thought to occur from the trapping of a vapor phase between the ice and lava (the ice transitions to steam, is trapped, and acts as a lubricant between the ice and lava). The existence of this trapped gas may also act as a buffer for heat flow between the lava and ice, which would melt the ice slower and allow the lava to advance further before sinking into the ice.


Formation of bubbly Limu o Pele surface in experimental lava flow. Liquid water and stream from the melting of the ice blocks below the lava is incorporated into the lava. The steam expands within the lava and forms large bubbles that then solidify, known as Limu o Pele. Image is from the main article.

Rapid and extensive formation of large bubbles (Limu o Pele, see figure 2) occurred within the lava during the no-sand experiments. This may be the first published demonstration of large-scale Limu production with water originating underneath lava. The abundance of bubbles that formed as lava flowed across the ice indicates that there may be a strong relationship between external water incorporation and the formation of Limu.

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