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Volcanoes. What is a Volcano?. A volcano is an opening in Earth’s crust that releases lava, smoke and ash when it erupts. Non active volcanoes are called dormant. The hole from which the magma emerges is called a vent.
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What is a Volcano? • A volcano is an opening in Earth’s crust that releases lava, smoke and ash when it erupts. • Non active volcanoes are called dormant. • The hole from which the magma emerges is called a vent. • http://video.nationalgeographic.com/video/player/environment/environment-natural-disasters/volcanoes/volcano-lava.html
Cinder Cone Volcano • Is the smallest and most common of the three types of volcanoes (most less than 300m) • Has steep sides and a bowl shaped crater at the top • Known for violent, explosive eruptions • Streaming gases carry liquid lava blobs into the atmosphere that fall back to earth around a single vent to form the cone. The volcano forms when ash, cinders and bombs pile up around the vent to form a circular or oval cone.
Cinder Cone Examples Krakatau, Indonesia La Poruna, Chile Paricutin, Mexico
Cinder Cone Volcano Diagram Vent Fine Ash Magma Cinder
Shield Volcanoes • Made of gently sloping layers composed entirely of cooled lava. • Low, broad shape formed by hot spots • Shield volcanoes are the largest of the 3 volcanoes. • Made of layers upon layers of cooled lava, ash is rare in shield volcanoes. • They do not erupt violently • The Hawaiian Islands are shield volcanoes • A hot spot is an area of volcanic activity produced my magma rising from the mantle. The temperature under the crust at a hot spot is much higher than elsewhere. The causes the magma to be forced upward through cracks in the Earth’s crust.
Examples of Shield Volcanoes Mauna Loa, Hawaii Ilgachuz Range, BC (Extinct) Kilauea, Hawaii Mount Edizza, BC
Composite Volcano • Is made of alternating layers of lava and cinder/ash. • The eruption may be quiet or violent and is intermittent (hundreds or thousands of years of inactivity separating a few years of activity.) • Most Complex • Formed by melting of crust when colliding with other rock surfaces (subduction) • Can be very large because of their long lives and resistance to erosion.
Examples of Composite Volcanoes Mount Baker • Active Volcano • 3285m • Last eruption was in the 1800’s, but eruption of hot fluids and gas in the late 1970’s show the volcano is still active • Glaciers cover Mt. Baker – an eruption would not only produce large quantities of ash, but create volcanic debris flow, floods, and landslides that would cause extensive damage in BC.
Examples of Composite Volcanoes Mount St. Helens • Active Volcano • 2950m • Explosive eruption was on May 18, 1980 – the rock on one side started to bulge a few days prior and there were several earthquakes • 400 km2 of forest was leveled and 24 km of valley was covered by debris flow • The eruption cloud rose over 20 km and ash deposits were 7- 10 cm deep • http://www.fs.fed.us/gpnf/volcanocams/msh/
Examples of Composite Volcanoes Mount Meager • Dormant Volcano in BC • The oldest known eruption was 2.2 million years ago • The ash plume from the last eruption travelled into Alberta • A lava flow dammed the Lillooet River • The pumice created in subsequent eruptions made Canada’s only pumice mine possible, on the northeast side of Mt. Meager • The explosive nature of Mt. Meager’s past eruptions has caused scientists to infer that the volcano is a threat to Pemberton and the Lillooet River area.
RING OF FIRE • Volcanoes often form along plate boundaries • The volcanoes encircling the Pacific Ocean are called the RING OF FIRE. • The Ring of Fire is composed over 75% of the world's active and dormant volcanoes.
Volcanoes are so DANGEROUS, so why do people live near them? • People live close to volcanoes because the soil is very fertile. Volcanic ash is rich in nitrogen, which makes the soil ideal for growing plants, fruits and vegetables. • Sometimes communities are wiped out due to the volcano. The volcanoes in BC cause very little personal or economic damage because they are located in areas that are not very populated.
Intrusive Volcanic Features • Most magma never reaches Earth’s surface. • Instead magma cools slowly underground and produces rock bodies that could become exposed later by erosion.
Volcanic Neck • Core of the volcano left behind after the softer cone has been eroded. Black Tusk, Garibaldi is an example.
Sill • Formed when magma flows parallel to the layers of rock and then hardens
Dike • Formed when magma flows across layers of rock and hardens
The Relative Age of Rocks • Geologists can use their knowledge of intrusive volcanic features and faults to understand the geologic history of rock layers. • The Principle of Superposition can be used to determine the relative age of rocks. In undisturbed layers of rocks, the oldest rocks are on the bottom and the youngest rocks are on the top. Sediments are often deposited in horizontal beds, forming layers. • Relative age – its age compared to other things – not exact. If layers of sedimentary rock are moved by a fault, you know that the layers had to be there first before a fault could cut through them. Therefore the relative age of the rocks is older then the relative age of the fault. • Complete Pardon My Intrusion pg 281
Absolute Age • Earth is approx. 4.6 billion years old! • Absolute age, is the age of an object. • Geologist determine absolute age by using properties of some of the atoms that make up the object.
Geologic Time Scale • Determining the relative age and absolute age of animals and plants that lived on Earth in the past has allowed scientists to create a geologic time scale. The geologic time scale divides the history of Earth into small Eras. The division of Eras is based on geologic events and the fossil record of the appearance and disappearance of living things.
