Underwater and coastal landslides can also trigger tsunamis. Large landslides caused by eruptions can create dams that block rivers and bury roads, bridges, and homes. Landslides can be caused by earthquakes or high rainfall, but volcanic activities such as magma intrusions and volcanic gas explosions can also be triggers. In contrast with a lahar, a landslide involves failure of the slope of the volcano itself. Landslides are masses of rock and soil that slide rapidly due to gravity. Helens, Washington, have travelled up to 60 miles away from the volcano. Lahars can travel along river valleys for much greater distances than lava and pyroclastic flows, presenting unique risks for communities in these areas. Lahars can do serious damage to river valleys and flood plains, and can bury entire villages, as occurred during the 1985 eruption of Nevado del Ruiz, Colombia. The size of the lahar usually increases as it travels down the slope and picks up more debris. ![]() Lahars are mainly associated with steep-sided volcanoes and they can vary in their size and speed. Lahars are a type of fast-moving volcanic debris flow consisting mostly of water, ash, and rock fragments with the speed of a fast-moving river but the consistency of cement. They can occur either during an eruption or at other times in response to high rainfall events. Some notable examples of recent pyroclastic flows are the eruptions at El Chicón, Mexico (1982) and Mount Pinatubo, Philippines (1991).ĭebris flows on volcanoes are a mixture of rock, ash, soil, vegetation, and water that flow down the slope of a volcano, sometimes funneling into river valleys. ![]() Serious injuries and deaths are often associated with pyroclastic flows due to their high speeds and destructive effects. A pyroclastic flow will destroy almost everything in its path, cause fires and floods, and bury everything under a mixture of rock, ash, and accumulated debris. The flows generally travel three to ten miles (five to fifteen kilometers) from the volcano. These flows are mainly associated with volcanoes that have explosive eruptions, and they move down the volcanic slope at speeds greater than 50 miles per hour (80 kilometers per hour). Pyroclastic flows are a mixture of ash, volcanic gas, rocks, and lava that generally reaches temperatures of 390-1300☏ (200-700 ☌). The ongoing eruptions at Kilauea, Hawaii are a well-known example of a lava flow. However, the high temperatures of lava flows may cause fires, and anything in the path of the lava flow will become encased in a thick layer of rock. Deaths and injuries from lava flows are not common because flows are typically quite slow (walking-running pace or slower). Others are faster-moving and may look almost like rivers of flowing honey. Many lava flows are slow and rugged, looking like a moving pile of rocks. Lava flows are what they sound like: lava (molten rock) flowing directly from a volcanic vent or fissure. Geological Survey and state geological surveys. volcanoes are monitored closely by the U.S. There are 169 active volcanoes in the U.S., chiefly in Alaska, California, Hawaii, Oregon, and Washington. ![]() Therefore, hazards detailed below are not necessarily relevant to every volcano. Some volcanoes typically produce highly explosive eruptions, such as in the subduction zones of Alaska and the Pacific northwest, and others produce less energetic eruptions, such as in Hawaii. ![]() There are many different kinds of hazards associated with volcanic eruptions, depending on the type of volcano and eruption.
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