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Volcanic activity. Classification of igneous rocks. Distribution of main volcanoes. Fujiyama, Japan. Mount St. Helen before May 18, 1980. Mount St. Helen after 1980. 400 km 2 of devastated area. Trees 25 km away from Mt. St Helen. Gases at 800 °, Mount St. Helen eruption.
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400 km2 of devastated area. Trees 25 km away from Mt. St Helen
Violent or “gentle” eruptions? Magma composition is the main factor
Fluid basaltic lava emitted from the flank eruption on Kalauea, Hawaii Velocity up to 30 km/h
Dissolved gases • Confining pressure • Volume increase with drop of confining pressure Basaltic magma fountains (generally harmless)
Material extruded during an eruption • Lava flow • Gases • Pyroclastic material
Viscose lava of intermediate to felsic composition “aa” type of flow Velocity 5-50 m/h
Eruption into water Pillow lavas
Gases • Gases constitute 1-6% of total erupted material but is thousand of tons per day Hawaiian eruptions: - 70% water vapor - 15% carbon dioxide - 5% nitrogen - 5% sulfur - Rest is chlorine, hydrogen, argon
Pyroclastic rocks or pyroclastics are clastic rocks composed solely or primarily of volcanic materials. Pumice deposits
Volcanic bombs Bombs ejected as incandescent lava; solidify in air
Volcanoes (terms) • Crater (D < 1 km) • Caldera (D > 1 km) • Vent – pipeline connecting with magmatic chamber • Parasitic cone • Fumaroles – emit only gases
Shield volcanoes are built primary of fluid basalts lava flows
Mauna Loa - shield volcano in Hawaii Largest in the world. Its total height is 9 km 170 m.
Cinder cones Cinder cones and craters in Arizona
Composite cones or stratovolcano • Most violent type of volcanic activity • Pompeii 79 A.D. is example
Mt Pelée, Martinique, 1902 • Eruption of Mt Pelée • Nueeardente (glowing avalanches) • travelled 6 km at 33m/s (approx. 200 km/h) • temperature: 700 degrees C • Destroyed town of St Pierre • Killed 28,000 people in 3 minutes • 2 survivors in St Pierre
Lahar of stratovolcano eruptions • Volcanic ash and debris saturated with water • Move 30 km per hour
2 Mechanism of caldera formation
Continent of Atlantis • Collapse of Minoan civilization 1500 B.C. • Caldera 14 km across
Volcanic necks • Formed due to erosion • Pyroclastic rocks are weak • Vent rocks are resistant to erosion