VOLCANOES YEAR 7

3. VOLCANIC ACTIVITY Lava begins as magma, formed in the asthenosphere. It rises toward the surface, into any cracks in the rock above. The gases form bubbles. When an opening develops in weak rock on the surface, a volcano erupts. When a volcano erupts, the force of expanding gases pushes magma from the chamber through the pipe until it flows or explodes out of the vent.

Inside a volcano: Magma chamber: magma is collected there Pipe: long tube in the ground that connects the magma chamber to Earth's surface. Vent: opening where molten rock and gas leave the volcano. Lava flow: area covered by lava as it pours out of a vent Crater: bowl-shaped area that may form at the top a volcano around the volcano's central vent.

Pipe Magma Chamber

The force a volcanic eruption depends on different things related to the magma: Amount of gas dissolved Temperature Silica content (Silicon plus Oxygen)

Type of volcanic eruptions: Quiet eruptions Magma low in silica, low viscosity and flow easily. I.e.: Hawaii volcanoes Explosive eruptions Magma high in silica, high viscosity, making it thick and sticky. I.e.: Mount St. Helens Explosive eruption breaks the lava into fragments that quickly cool and harden into pieces of different sizes: ash (small pieces) and bombs (large pieces) Pyroclastic flow occurs when an explosive eruption hurls out ash, bombs, gases…

QUIET ERUPTION (KILAUEA) EXPLOSIVE ERUPTION (MT ST.HELENS)

PYROCLASTIC FLOW BOMB

VOLCANO HAZARDS Both type of eruptions can cause damage far from the crater’s rim Quiet eruption: Lava flows from vents, setting fire to and then burying everything in its path. It can cover large areas with a thick layer of lava Explosive eruption: Volcano can belch out hot clouds of deadly gases, ashes, bombs… Volcanic ashes can bury entire towns. If it becomes wet, the heavy ash can cause roofs to collapse. If a jet plane sucks ash into its engine, the engine may stall. Eruptions can cause landslides and avalanches of mud, melted snow and rock

Geologist have been more successful in predicting volcanic eruptions than earthquakes. Geologist monitor volcanoes checking different parameters and small earthquakes around it, caused by the movement of magma: Surface changes in elevation (magma moving underground) Gases (escaping from the volcano) Temperature increase in the underground water (magma is nearing the surface)

Stages of a volcano (From less than a decade to more than 10 million years): Active or live: it is erupting or has shown signs that it may erupt in the near future. Dormant or sleeping: scientist expect to awaken in the future and become active. Extinct or dead: it is unlikely to erupt again