Volcanic Eruptions

Hawaii – many myths about Pele, the fire goddess of volcanoes Pele lives in the depths of Hawaii’s erupting volcanoes When Pele is angry, she causes a volcanic eruption Pele’s hair type of volcanic rock As lava stretches and hardens into thin strands

Magma Reaches Earth’s Surface Inside a volcano Magma chamber – beneath a volcano, magma collects in a pocket Magma moves upward through a pipe Molten rock and gas leave the volcano through an opening called vent, at the top of the volcano Vents can form on the side of the volcano

Lava flow an area covered by lava as it pours out of a vent Crater is a bowl-shaped area that may form at the top of the volcano around the central vent

A Volcanic Eruption The carbon dioxide in the magma expands and forms bubbles, which rush to the surface, these dissolved gases are under pressure When a volcano erupts, the force of the expanding gases pushes magma from the magma chamber through the pipe until it flows or explodes out the vent.

Kinds of Volcanic Eruptions Quiet Eruptions – low in silica Low silica – magma has low viscosity and flows easily Lava flows easily from the vent, and flows for many kilometers, can produce both pahoehoe and aa

Explosive Eruptions – magma high in silica, high viscosity magma is thick and sticky High viscosity magma builds up in the volcano’s pipe, gases build up pressure until they explode. Pebble-size particles are called cinders Large pieces are called bombs (baseball to car size) Pyroclastic flow occurs when an explosive eruption hurls out a mixture of hot gasses, ash, cinders, and bombs

Obsidian forms when lava cools very quickly, giving it a smooth, glossy surface like glass Pumice forms when gas bubbles are trapped in fast cooling lava, leaving spaces in the rock

Volcano Hazards Quiet Eruption, lava flows setting fire and burying anything in its path, can cover large areas with thick layers of lava

Explosive Eruptions puts out hot clouds of deadly gases, ash, cinder, and bombs. Ash can bury entire towns If ash becomes wet, becomes heavy and collapse roofs Planes can suck in ash and make the engines stall Cause landslides, avalanches of mud, melt snow and rock

Stages of Volcanic Activity Volcanoes can last from less than a decade to more than 10 million years Active, (alive) volcano is one that is erupting or has shown signs that it may erupt in the near future Dormant volcano may awaken in the future and become active Extinct (dead) unlikely to erupt again