Chapter 18. Volcanism

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1 Chapter 18 Volcanism

2 Ring of fire contains 66% of world s active volcanoes

3 Convergent : Divergent: Icelandic Eruption Mount Etna

4 Different Kinds of eruptions: Volcanic activity is controlled by plate tectonics, because plate movements relate to where sources of magma originate inside the earth. Nearly all active volcanoes are located in one of three plate tectonic settings: Subduction zones at convergent plate boundaries Example: Volcanoes lining the trenches of the Pacific Ocean, forming the Pacific Ring of Fire. Rifting and sea floor spreading at divergent plate boundaries, Example: Volcanic eruptions at mid-ocean ridges, and in some rift zones on the continents, like the East African Rift Valley. Hot spots Example: The Hawaiian Islands and the Galapagos Islands. The violence of a volcanic eruption depends on the magma s viscosity and gas content. The more viscous (thick) and more gaseous the magma, the more explosive the eruption.

5 Hot Spots

6 Hawaii Hawaii- the Hot Spot video Hawaii is a formed by a the Pacific Plate sliding over a stationary lava plume called a Hot Spot. The older islands, which are no underwater, used to be over the hot spot but the plate has slowly moved. A new island, Loihi, is already being formed presently over the active hot spot.

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8 Lava Bombs Magma Chamber

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10 Caldera Magma Chamber Crater

11 Shield Cinder Cone Composite (Strato)

12 Shield: Hawaii Types of Volcanoes Shield Cinder Cone: Paricutin Composite Cinder Cone Composite: Mt Saint Helens

13 Shield: Cinder Cone: Composite:(strato) Above: Photos the eruption of Paricutin Volcano, Mexico, a classic example of a cinder cone. Above: This cone is one of two cinder cones called the Red Cones located south of Long Valley Caldera in California. These basaltic cones were erupted about 5,000 years ago.

14 Viscosity is a measure of a fluid s resistance to flow. The main factor that determines the viscosity of magma is its silica (SiO2) content. The more silica in the magma, the more viscous it is. The more viscous (silica-rich) the magma, the more violent the eruption

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16 Supervolcanoes are giant rhyolite volcanoes that form over continental hotspots. Resurgent caldera eruptions are by far the largest and presumably most destructive of all types of volcanic eruptions. Two examples are Yellowstone and Toba (which was so violent that it put the planet into an Ice Age 75,000 years ago. Bottom Image: The Yellowstone Volcano is the relic of three monstrous eruptions that occurred 2mya, 1.3mya, and 600,000ya. Each eruption left collapse calderas ~50km across. As magma continues to rise beneath the caldera, it raises a resurgent dome in its surface.

17 Yellowstone National Park is actually a super volcano! The park is located within a 25mile wide caldera. Yellowstone has been shown to have had at least six mega-collasal eruptions, generally every 600,000 to 650,000 years. Evidence is showing the formation of a new eruption caldera, however, it is likely to erupt in about 10,000 years. Evidence of a major eruption would be evident days to months before the eruption would occur.

18 Hazards of Violent Volcanoes A. Lava B. Pyroclastic Flow C. D. Lahars E. Volcanic Ash F. Release of Volcanic Gases G. Volcanic Weather Mount Saint Helens on May 18 th 1980

19 Fluid basalt lava flows are called Hawaiian type lava and can come in two varieties. Aa -Slow and chunky yet sharp when cooled lava Lava is molten magma that flows out and onto the Earth s surface. Lava flows are typically formed from low viscosity mafic magma that erupts at divergent boundaries and hot spots. Pahoehoe -Smooth and runny lava

20 Merpal Pinatubo Pinatubo Mt. Saint Helens All that remains of a of a building, those are steel beams Pinatubo

21 A lahar is a rapid-moving mudflow that occurs when the snow at the summit of a volcano melts rapidly due to the heat from magma moving upward through the volcano. These mudflows can bury towns in minutes moving up to 100mph with the weight of up to 2 ton per square meter! Volcanic Mudflows or Lahars form by mixing water with loose volcanic ash and debris on the flanks of a volcano. As the mud moves downslope, it gathers rocks of all sizes accelerating as it goes.

22 Ash falls form when an eruption column of tephra and gas is blown into the air by an explosive eruption. The eruption column can rise up more than 20 km into the atmosphere. Chile Tephra is a general term for any size of fragmental material blown out of a volcano. Pinatubo New Guinea

23 The gas content of a magma also relates to its behavior. A magma with low gas content will tend to flow out of a volcano as relatively quiet lava.. The higher the gas content, the more violent the eruption. Gases emitted during volcanic eruptions may be toxic and/or corrosive. The most common hazardous gas is CO2. Carbon Dioxide is deadly to people, animals, and trees in high concentrations Dead trees and cattle from gases given off by nearby volcanoes The composition of the gases in magma are: Water vapor Carbon Dioxide Minor amounts of sulfur dioxide, hydrogen sulfide, chlorine, and flourine gases.

24 Volcanic Thunderstorm