Volcanic Mud Slides Causes
Country: New Zealand
Date: Summer 2009
What causes a lahar on new Zealands Mt Ruapehu?
Lahars are not unique to New Zealand. Lahars are mud flows that originate on
volcanoes. These viscous flows are produced when heat from a volcano melts
snow near the vent, thus producing water. The water mixes with the pyroclastics
(rock fragments previously ejected from a volcano) on the flanks of a volcano to
form a mud flow (otherwise known as a lahar).
Ruapehu is a stratovolcano which means that the flanks of the volcano are
represented by numerous, repeating layers of lava and pyroclastics. The summit
elevation is 2707 meters, so the vents are commonly surrounded by snow.
Common eruptive materials from volcanoes include lava, pyroclastics, gases, and
water. Water eruptions are known as phreatic eruptions and Ruapehu has a lake at
its summit, known as Crater Lake. The lahars of Ruapehu have an abundant source of
water (Crater Lake and snow) to mix with ample pyroclastic materials and produce a
Have you ever considered why snow is more common on the top of a volcano neat the
Leslie Kanat, Ph.D.
Professor of Geology
Department of Environmental Sciences
Johnson State College
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Update: June 2012