volcanism n.
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  1. Volcanism

  2. Types of volcanic activity • Fissure eruptions • Shield volcanoes • Cinder cone volcanoes • Composite volcanoes ( andesite volcanoes)

  3. Fissure eruptions • A simple crack in the lithosphere from which molten volcanic rock may spew on the ocean floor Found at mid-ocean ridge or east coast of South America and west coast of Africa

  4. Columnar jointing • When basaltic lava flows from a fissure area creating a plateau. When the lava cools it tends to fracture into cylindrical columns called columnar jointing.

  5. Shield Volcanoes • Occur predominantly on ocean floors, • They have gentle slopes and may be kilometers in diameter • Basaltic lava- like wet concrete • Hawaiian Islands forming over a hotspot are all shield volcanoes. Mauna Loa, largest peak rises about 10km. From seafloor

  6. Cinder Cone volcanoes • Predominantly found on continents • Have steep sides and consist of layers of cinders and ash. • Violent explosive eruptions are associated with cinder cone volcanoes as the less fluid andesitic lavas associated with cinder cone volcanoes. • Violent erupted material is collectively referred to as pyroclastics

  7. Composite volcanoes (andesitic) • Volcanoes, andesitic ones especially, erupt different materials at different times • Built layer cake fashion out of lava and ash • Most of the volcanoes formed over the subduction zones are composite volcanoes. • They have a symmetrical shape and are snow and iced capped. • Mt St Helens erupted in May 1980 much of the damage was caused by Lahars- Mudflows

  8. Hot Spots • Super heated plumes in the upper region of the mantle or asthenosphere • Pressure from the lithosphere above keeps this area from melting • If a crack occurs in the lithosphere, the pressure from above is reduced and the magma then takes a liquid state and flows freely up onto the earth’s surface • Hawaiian Islands- plate has been moving NW over the hotspot

  9. Important Features created by intrusive volcanic activity • Dike • Sill • Laccolith • Volcanic Neck • Batholith • Define these and tell me about them • Draw Figure 9.8 Pg 22

  10. Features created by extrusive volcanic activity • Lava- igneous rock that has reached the surface of the earth. Continental volcanic eruptions often do not involve a lot of lava • Pyroclastics: refers to any material blasted out of a volcano- Dust and ash caused more problems locally than globally

  11. Caldera • A huge volcanic crater that is formed in one of two ways---A) as a volcanic eruption begins the magma chamber below the mountain begins to feed molten rock to the surface---If a lot of lava flows out of the volcano the magma chamber below may begin to empty faster than it can be refilled: the mountain loses it support and collapses in on itself creating a huge crater • B) if the eruption is particularly violent the entire top for the mountain may be blown off to form a cladera.

  12. More extrusive volcanic activity • Lahars: Volcanic mudflow • Nueesardentes- pryroclasic flows of super heated denser than air gas exceeding 1000 degrees Celsius in temperature and 160 km per hours in speed

  13. Benefits of volcanoes • Eruptions that occur on the ocean floor can create new land as is the case in Hawaii and Iceland- many island chains are volcanic in origin • Volcanic dust is loaded with nutrients and with each eruption more nutrients are deposited on the surrounding landscape. Farmers in Indonesia, for example, have farmed the slopes of volcanoes for hundreds of years, reaping the benefits of the rich soil. • Hot magma close to surface in volcanic regions can be a source of environmentally clean geothermal energy. Throughout the Pacific Ring of Fire the potential exists for geothermal energy. In Iceland more than 85% of the homes are heated geothermally; in north-western California nearly 60% of the electricity is produced by geothermal power plants.

  14. Benefit of volcano • Volcanoes are major tourist attractions. Millions of people each year visit Mount. St Helens National Volcanic Monument in Washington State. Other • Volcanoes around the world are also popular tourist destinations. • Hot springs and geysers, a result of volcanic activity, also attracts many visitors each year.