1. Mrs. Gordon Earth Science Tuesday, July 03, 2018
Notes 17 – Volcanoes
Mrs. Gordon
Earth Science
Tuesday, July 03, 2018

2. 10,200-foot Redoubt Volcano about 100 miles southwest of Anchorage
1. What is a volcano?
A. Volcano – a weak spot in Earth’s crust where magma rises 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

3. 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

4. C. Volcanic Activity Terms:
~ Pyroclastic flow – Massive cloud of HOT ash, rocks, and gases
~ Lahar – Gigantic mud flow
~ Caldera – depression formed when a volcano collapses (Yellowstone, Crater Lake)

5. 2. Where do volcanoes occur?
Most occur near plate boundaries.
~ Ring of Fire – a major volcanic belt that rims the Pacific Ocean.

6. Eruption in April 2010 of Iceland’s volcano Eyjafjallajokull.
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.

7. B. Convergent boundaries - (Cascades = Mt. St
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.

8. C. Hot spots - (Hawaii, Yellowstone) – a large concentration of heat in one area, magma burns through the crust.

9. 3. Types of Volcanoes:
Fissure Eruption

10. Attach Diagram across from Notes 17

11. low silica = quiet eruptions
Shield Volcano –
low silica = quiet eruptions
Galapagos shield volcano

12. B. Cinder Cone

13. C. Composite Volcano (stratovolcano) –
high silica content = violent eruptions

14. 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.