8Magma Types What type of Magma influences what type of eruption Mafic Magma–Hot and Thin: Magnesium and Iron (common ocean)Cools Rapidly and crust slowly deforms (Like pudding crust) Ropy Lava and rock called PahoehoeCools Rapidly and crust quickly deforms or is thick forms chunky lava and rock called AaLava Flows out of fissures ocean floor forms blobs and rock called Pillow lavaGas escapes easily and flows like a riverFelsic Magma-Silica Rich (common crust)
14Lava can move underground in a Tube forms a lava tube After cooling crystallize to form rock
15Lava-Formation of Lava Trees near Kilauea- Effect of Quenching Lava
16Lava-Wahalua Visitor Center in Hawaii Volcanoes National Park engulfed by lava1989
17Magma Type Influences eruption style 2. Felsic Magma-Silica Rich (common crust)Large amount of Trapped gases-water vapor and CO2Explosive! Volcano Ejects Pyroclastic Material (Pyroclastic Flow)Pyroclastic MaterialEnormous amount of rock fragments, volcanic glass fragments, and volcanic bombsVolcanic Ash (<2mm), Dust (<.25mm)Lapilli- “Little Stones” (<64mm)
18Pyroclastic Flow-Ash Cloud over Plymouth On July 27, 1996 from Soufri`ere Hills West Indies
19Mount Pinatubo(Phillipines)June 15–16, 1991Pyroclastic Flow Killed 350 people and destroyed a U.S. military baseNearly 1-ft depth of ash covered buildings over a 40-km radiusHuge cloud of ash 400 km wide into nearly 40 km elevationAffected global climate (cooler summer the next year; global temp differences −0.5°C, ~1°F)
20Pyroclastic Flows -St. Pierre, Martinique West Indies Destroyed by a from Mont Pele’e 1902 Explosion-A convicted murderer sole survivor
21Harry Glicken at Mt. St. Helens Observation Site in 1980 before the eruption that blew off the top of the mountain. He is looking toward the bulge on the flank of the volcano. This is the post that when it erupted the observation post was destroyed and the geologist at the site was killed.
22Pyroclastic Flow From Mount St. Helens Mount St Pyroclastic Flow From Mount St. Helens Mount St. Helens May 18, 1980, erupted after a 120-year dormancy Earthquake (4–5 magnitude)Lateral blast impacted 19 miles at 1000 km/h Mudflows reached nearly 100 km (60 miles) away Ash/tephra materials spread over WA, ID, and west MTIts maximum altitude (peak) reduced by 450 meters (over 1476 ft)Killed 57 people, damaged 100 homes, 800 million feet of timber: Total cost $3 billion
23Volcanic Materials - Pyroclastics Blocks from KilaueaVolcanic Ash from Mt. St. HelensBombs may form streamline shape in the air from Mt. KeaVolcanic Breccia at Mt. Lassen
24Volcanic BombKilauea threw a 14 ton bomb ½ mile !!!!! Stromboli threw a 2 ton bomb 2 miles!!!
34Caldera-The magma chamber below a volcano is emptied and the cone collapses and leaves a large basin shaped depression
35June 1912 eruption of Novarupta Volcano altered the Katmai area dramatically the largest eruption in the 20th centurySevere earthquakes rocked the area for a week before Novarupta exploded with cataclysmic forcemore than 40 square miles of lush green land lay buried beneath volcanic deposits as much as 700 feet deep !for two days a person could not see a lantern held at arm's length
37Predicting Volcanic Eruptions Classification by activity: Knowledge of previous eruptions can help predict futureActive:Dormant:Extinct:Volcanic ActivitySmall EarthquakesTemperature changesNumber of EarthquakesIncrease In strength of earthquakesBulging at the surface