1. 18.3: TYPES OF VOLCANOES
SWBATS:

2. ANATOMY OF A VOLCANO Below Earth’s lies the magma chamber.
Hot, less dense magma rises to the surface at a volcanic vent.
Vent: opening in Earth’s crust through which lava erupts and flows out onto the surface.
Lava cools and solidifies around the vent and can eventually form a mountain.
The crater is located on the top of volcano
Crater: Bowl-shaped depression, usually less than 1 km in diameter, that forms around the central vent at the summit of a volcano.
Caldera: large crater, up to 50km in diameter that can form when the summit or side of a volcano collapses into the magma chamber during or after an eruption.

3. 3 MAIN TYPES OF VOLCANOES
SHIELD VOLCANO
CINDER CONE VOLCANO
COMPOSITE

4. SHIELD VOLCANO
DESCRIPTION/DEFINITION:
Broad volcano with gently sloping sides built by nonexplosive eruptions of basaltic lava that accumulates in layers.
TYPE OF MAGMA/LAVA:
Basaltic magma
TYPE OF ERUPTION:
Quiet/Nonexplosive
Low viscosity
Small amounts of gases
Low silica content
EXAMPLE OF THIS VOLCANO:
Mauna Kea in the Hawaiian Islands
Iceland

5. CINDER-CONE VOLCANO DESCRIPTION/DEFINITION:
Steep-sided, generally small volcano that is build by the accumulation of tephra around the vent.
TYPE OF MAGMA/LAVA:
Andesitic
More water and silica than shield volcanoes
Medium viscosity
Lots of gases
TYPE OF ERUPTION:
More explosive than shield volcanoes
EXAMPLE OF THIS VOLCANO:
Izalco Volcano, El Salvador
Paricutin Volcano in Mexico

6. COMPOSITE/STRATOVOLCANO
DESCRIPTION/DEFINITION:
Large, sloping volcano built by violent eruption of volcanic fragments and lava that accumulate in alternating layers.
TYPE OF MAGMA/LAVA:
Volcanic fragments (tephra) with alternating layers of lava
Large amounts of silica, water and gases
Rhyolitic/Granitic
TYPE OF ERUPTION:
Violent eruptions
EXAMPLE OF THIS VOLCANO:
Cascade Range – Mt. St. Helens and Mt. Rainier.
Mt. Shasta in CA
Mt. Fuji in Japan

7. SIZE AND SLOPE OF A VOLCANO
Shield volcanoes – largest size, gentle slopes
Cinder-cone volcanoes – smallest size, steep slopes
Composite volcanoes – medium size, moderate slopes
Size and slope are a result of:
Materials that make up each volcano
Vegetation that grows on the volcanoes slope
Local climate
Eruptive history of the volcano

8. VOLCANIC MATERIAL dust = less than 0.25 mm in diameter
Tephra: rock fragments, classified by size, that are thrown in o the air during a volcanic eruption and fall to the ground.
Types of Tephra – smallest to largest
dust = less than 0.25 mm in diameter
ash = larger than dust but less than 2 mm in diameter
lapilli “little stones” = larger than 2mm but less than 64mm in diameter
volcanic blocks = size of a car or small building
volcanic bombs = large blobs of lava forcefully ejected from a volcano

9. PYROCLASTIC FLOW Pyroclastic flow:
swift-moving, potentially deadly clouds of gas, ash, and other volcanic material produced by a violent eruption.
Pyroclastic flows are so deadly because they:
Can travel close to 200km/h
May contain hot, poisonous gases.
Temperatures can exceed 700 degrees C.
Most deadly pyroclastic flow:
1902 – Mount Pelee – Island of Martinique in Caribbean.
More than 29,000 people killed (suffocation or burned)

10. WHERE DO VOLCANOES OCCUR?
CONVERGENT PLATE BOUNDARIES
Plates moving together to create subduction zones
Oceanic plate descends into the mantle – eventually melts
Magma is then forced upward through the plate above – creating a volcano
EX:
Circum-Pacific Belt “Ring of Fire”
Mediterranean Belt

11. WHERE DO VOLCANOES OCCUR?
DIVERGENT PLATE BOUNDARIES
Plates are moving apart.
Magmas is forced upward to fill in the cracks as plates separate
Areas of faults and fractures are called rift zones
Usually occurs underwater – forming new seafloor
EX:
Mid-Atlantic Ridge
Iceland (volcano at sea level)

12. WHERE DO VOLCANOES OCCUR?
HOT SPOTS
Volcanoes occur far from plate boundaries
Regions of Earth’s mantle that contain high temperature plumes of magma
Magma rises to the surface and forms volcanoes
Plumes do not move laterally – only vertically
Plate moves over the top of the plume
Leave a trail of progressively older volcanoes
EX:
Hawaiian Islands

13. CIRCUM-PACIFIC AND MEDITERRANEAN BELTS
Circum-Pacific Belt:
Pacific Ring of Fire – along west coasts of North and South America, across the Aleutian Islands and down the eastern coast of Asia.
Example of Volcanoes:
Cascade Range – Mt. Shasta, Mt. Lassen, Mt. St. Helens), Mount Pinatubo in Philippines
Mediterranean Belt:
Smaller belt found in Europe
Examples of volcanoes:
Mount Etna and Mount Vesuvius (both composite volcanoes)

14. HOW THE HAWAIIAN ISLANDS WERE FORMED
Pacific plate moved over a hot spot.
Oldest island – Kauai – inactive now because it no lover over the hot spot.
Youngest island – Hawaii – Most active volcano – Kilauea – currently over the hot spot.
Loihi is another volcano forming currently on the seafloor east of the big island of Hawaii – May eventually forma a new island.
Studying the volcanoes helps to study the rate at which the plate moves

15. OLDEST AND YOUNGES VOLCANOES IN THE HAWAIIAN-EMPEROR VOLCANIC CHAIN
Part of the Hawaiian-Emperor volcanic chain (5800km long)
Hawaiian Islands – youngest
Oldest seamount - Meiji is about million years old
Daikakuji Seamount shows a bend in the chain = Change in direction of the Pacific Plate about 43 million years ago.

16. FLOOD BASALTS
FLOOD BASALT: erupt from fissures rather than a centeral vent and can form flat plains of plateaus rather than volcanic mountains
Ex:
Colombia River Basalts in Northwestern US cover 170,000 km3 of basalt
Decan Traps in India estimate to be 521,000km3