Transcript Notes 17 - Volcanoes re-done 2015

Notes 17 – Volcanoes
Mrs. Gordon
Earth Science
Tuesday, April 12, 2016
1. What is a volcano?
• A. Volcano – a
weak spot in
Earth’s crust where
magma can rise to
the surface.
Mount Etna in Sicily, Italy.
Lava pools at Hawaii Volcanoes National Park.
10,200-foot Redoubt Volcano about 100 miles southwest of Anchorage
B. Explosiveness:
– Silica (quartz) content –
• low silica = quiet eruptions = fluid and runny lava, LOW
viscosity like water
• high in silica = explosive eruptions
= thick and pasty lava, HIGH viscosity like honey
C. Volcanic Activity Terms:
~ Pyroclastic flow –
Massive cloud of HOT ash,
rocks, and gases
~ Lahar – Gigantic mud
flow
~ Caldera – depression
formed when a volcanic
summit collapses into a
partially emptied magma
chamber. (Yellowstone,
Crater Lake)
2. Where do volcanoes occur?
• Most occur near plate boundaries.
~ Ring of Fire – a major volcanic belt that rims the
Pacific Ocean.
• A. Divergent boundaries - (ocean floor,
Iceland) - two plates ripping apart and magma
squeezes up / between
Eruption in April 2010 of Iceland’s volcano Eyjafjallajokull.
Laki is a volcanic system, belonging to
Katla the central volcano in Iceland, and
was at the origin of the biggest volcanic
eruption on earth in historical times
(1783), in the form of a flood basalt.
• B. Convergent boundaries - (Cascades =
Mt. St. Helens) - one plate is pushed under
another, melts, and through convection,
magma rises up.
Picture by US Geological Survey
scientist, Austin Post, on May 18, 1980.
• C. Hot spots - (Hawaii, Yellowstone) – a
large concentration of heat in one area,
magma burns through the crust.
3. Types of Volcanoes:
• Fissure
Eruption
Attach Diagram across from Notes 17
A. Shield Volcano –
low silica = quiet eruptions
Galapagos shield volcano
B. Cinder Cone
C. Composite Volcano (stratovolcano) –
high silica content = violent eruptions
• D. Fissure Eruption – very low silica
– The greatest volumes of volcanic material come from fissure eruptions.
Most occur on the ocean floor. Ex: Snake River flood basalts, along the
Columbia River, seafloor spreading.