Ice-marginal lava flow
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Introduction to Glaciovolcanism
An ice marginal lava flow is a phenomenon associated with glaciovolcanism. Glaciovolcanism is the study of volcano and ice interaction, so essentially any and all volcanic activity that interacts with any sort of ice formation The science of glaciovolcanism relatively young in age because, to study it, people must overcome hostile environments. While young, the science of glaciovolcanism can give us clues to in order to reconstruct volcanoes from the past and answer questions regarding whether or not ice was present in a certain area, the thickness of the ice, the surface elevation of the ice sheet and finally the structure of the ice sheet. Glaciovolcanism is increasingly important for volcanic hazard awareness and preparedness, studying the Pleistocene climate record, possible relationships between deglaciation and volcanism, and finally possible Martian geoscience research.
There are three subdivisions of glaciovolcanism: supraglacial volcanism, subglacial volcanism, and ice-marginal volcanism. Supraglacial volcanism is the direct eruption of lava onto a glacier. Subglacial volcanism is the eruption of a volcano beneath of a glacier. Finally, ice-marginal volcanism is a volcanic eruption that does not erupt above or below a glacier, but the lava flow comes into direct contact with a glacier or large ice sheet's margins. Initially, the lava flow is like any other but when the lava reaches the margins of an ice sheet, the front of the lava flow cools very quickly and thus, forms a barrier (Figure 1). Behind this barrier, the lava begins to pool, ceasing the contact between the hot lava and cold ice. The barrier is left behind as the ice retreats, leaving a thick lava front, which is just a large, steep, and unstable cliff face.
A fantastic example of a natural lava dam formed from an ice-marginal lava flow is a phenomenon aptly named “The Barrier” in the Garibaldi Volcanic Belt. The Garibaldi Volcanic Belt is located in the northern part of the Cascade Ranges. The Barrier was formed when about 13,000 years ago Mount Price, one of the 13 volcanoes that make up the Garibaldi volcanic belt, erupted and sent a lava flow down Rubble Creek Valley and met the Cordilleran Ice Sheet
. The Cordilleran Ice sheet was a major sheet that covered a large part of North America including western Montana, northern Washington and just about all of British Columbia. In Figure 2, you can really see the steepness of the cliff face, which is where the lava flow met the ice sheet. The two lakes behind the dam are Garibaldi Lake and Lesser Garabaldi Lake, which formed after melt water pooled behind the lava flow wall. The Barrier, while 2 km away from the lake, is helping to hold in Lesser Garibaldi Lake. The problem here is that vertical slabs of lava that make up the Barrier Cliff occasionally collapse and form massive rock avalanches that move down the valley toward local residences.The biggest threat is the complete collapse of the damn, which is entirely possible due to volcanic activity and erosion. In the late 1800s, a debris flow from the Barrier created a large boulder field which gave Rubble Creek its name. Conditions are so bad that the area directly below the lava damn is considered uninhabitable and dangerous to human life.
A second example of ice-marginal lava flows can again be found in British Columbia, this time near the border of Alaska. The Hoodoo Mountain Volcano is located in Northwestern British Columbia The volcano formed underneath a glacier, making it a subglacial formation. The Hoodoo Mountain Volcano is a flat-topped stratovolcano as a result of its subglacial beginnings. Currently the volcano is surrounded on all sides, except the south, by glaciers. What does Hoodoo mountain have to do with ice-marginal lava flows? Well, the entirety of the mountain is also surrounded by enormous lava cliffs, ranging from 50m-200m in height, as seen in Figure 3. The clearest example of these lava cliffs is seen on the southwestern side of the mountain whereas the northern formation of these cliffs has been overridden by recent lava flows and glacial erosion. Scientists are able to diagnose these lava cliff formations as a result of ice-marginal lava flows because of specific features such as the "glassy" chemical composition of the lava and columnar jointing, which are evidence of fairly quick cooling of an erupted lava flow. Scientists are able to determine that about 80 thousand years ago Hoodoo Mountain was completely surrounded by ice. Also 80 thousand years ago, there was an eruption from Hoodoo Mountain and as the lava poured down the slope, the lava came into contact with the ice that completely surrounded the volcano and cooled very quickly, forming a barrier around the entire volcano. The lava cooled, pooled and as the glacial ice receded, it left behind massive lava cliffs.
Mount Raupehu is the tallest mountain on the Northern island of New Zealand. The massive stratovolcano is an excellent example of how scientists put historic glacial periods and volcanism together. Ice-marginal lava flows are a keystone in Raupehu’s history and are well displayed in the Wahainoa Lava Formation (Figure 4). The characteristic columnar jointing and massively thick lava barriers are evidence of major ice-marginal lava flows. Scientists have determined through geochronology that the volcano erupted about 15-51 thousand years ago and the lava flow came into contact with the surrounding valley floor glaciers and built up the enormous lava formations we see today. Using the eruption age and the ice-marginal lava flow data, scientists can gather when glaciers dominated Raupehu, how high an elevation the glaciers reached, which was about 1300m above sea level, and can use glaciovolcanism as a proxy reconstruct the paleoclimate of about 41-51 thousand and 15-27 thousand years ago.
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