Ice-marginal lava flow- Building Iceland’s Lava Barriers

An ice-marginal lava flow is a lava flow that comes into direct contact with a glacier or the margins of a large ice sheet. As the lava reaches the margins of an ice sheet, the front of the lava flow cools very quickly to form a barrier. 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 in the form of a large, steep and unstable cliff face.

The Barrier

The Barrier in British Columbia, Canada is a natural lava dam that formed when Mount Price produced a lava flow that travelled down the Rubble Creek valley and met the Cordilleran Ice Sheet about 13,000 years ago. Two lakes behind the lava dam, Garibaldi Lake and Lesser Garibaldi Lake, formed after meltwater pooled behind the lava flow wall. The vertical slabs of lava that make up The Barrier occasionally collapse to form massive rock avalanches that travel down the valley toward local residences. The biggest threat posed by The Barrier is a complete collapse of the lava dam due to volcanic activity or 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 unstable that the area directly below The Barrier is considered uninhabitable and dangerous to human life.