3Today we will look at: Where they occur “Continental Drift” & “Plate Tectonics”Types of volcanic eruptionsHistorical eruptions
4More than half en circle the Pacific Ocean. Volcano environmentsMost active volcanoes are located along, or near, the margins of the continents.More than half en circle the Pacific Ocean.The area in red, below, is called the "Ring of Fire."
5Plate-tectonics theory Alfred Wegener first proposed “Continental Drift” Theory in early 1900’s. This theory was widely criticized.Discovery of mid-ocean ridges gave birth to “Seafloor Spread” theory.The demonstration below shows the drift in reverse, ending with the super-continent “Pangea”.
6What drives plate tectonics ? One theory is that convection within the Earth's mantle pushes the plates, in much the same way that air heated by your body rises upward and is deflected sideways when it reaches the ceiling.Another theory is that gravity is pulling the older, colder, and thus heavier ocean floor with more force than the newer, lighter seafloor.
7Divergent boundaries (Seafloor Spread) As the two sides of the mountain move away from each other, magma wells up from the Earth's interior.It then solidifies into rock as it is cooled by the sea, creating new ocean floor.
8Convergent boundaries New crust is continually being pushed away from divergent boundaries, increasing the Earth's surface.The ocean crust subducts, or slides under, other pieces of Earth's crust.
9Collisional boundaries When two land masses meet, neither will slide under the other.They crumple and fold. Some pieces of land are thrust over or under other pieces. The result is a mountain range.
10Transform boundariesTwo plates move against each other, building up tension, then releasing the tension in a sudden and often violent jerk.This sudden jerk creates an earthquake.
11Hot SpotsThe Hawaiian volcanoes were formed by a hot spot that remained fixed as the pacific plate moved to the north west.
12Island ArcsOne plate sinks into a trench. A continuous series of earthquakes is created. The plate then starts to heat up at a depth of about 75 miles. certain magmas are melted and rise toward the surface, forming volcanoes.
13If the upper plate is oceanic, the volcanoes pile up until they poke through the surface of the ocean and form an elegant arc.
15Principal Types of Volcanoes Cinder cone volcanoesComposite volcanoesShield volcanoes
16Cinder cones are the simplest type of volcano are built from particles and blobs of congealed lava ejected from a single ventgas-charged lava is blown violently into the air, it breaks into small fragments that solidify and fall as cinders around the vent to form a circular or oval cone.have a bowl-shaped crater at the summit and rarely rise more than a thousand feet or so above their surroundings
17Composite volcanoes (stratovolcanoes) are typically steep-sided, symmetrical cones of large dimension built of alternating layers of lava flows, volcanic ash, cinders, blocks, and bombs and may rise as much as 8,000 feet above their basesMost have a crater at the summit which contains a central vent or a clustered group of vents
18Shield volcanoes are built almost entirely of fluid lava flows Lavas also commonly erupt from vents along fractures (rift zones) that develop on the flanks of the cone
19Strombolian-type eruption huge clots of molten lava burst from the summit crater to form luminous arcs through the sky
20"Vulcanian"-type eruption a dense cloud of ash-laden gas explodes from the crater and rises high above the peakSteaming ash forms a whitish cloud near the upper level of the cone
21"Hawaiian" eruptionsmay occur along fissures or fractures that serve as linear ventsmay occur at a central vent
22"Phreatic" (or steam-blast) eruptions driven by explosive expanding steam resulting from cold ground or surface water coming into contact with hot rock or magmathey only blast out fragments of pre-existing solid rock from the volcanic conduitgenerally weak, but can be quite violent in some cases(Mt St. Helens)
23“Plinian" eruptians Most powerful Involve the explosive ejection of relatively viscous lavaFast-moving deadly pyroclastic flows are common
25Mount St. Helens erupted on May 18, 1980. Power of a VolcanoThe following slides demonstrate the power of one of the better known American volcanoes.Mount St. Helens erupted on May 18, 1980.57 victims were claimed in the eruption.4 victims were in the restricted zone.The remaining 53 victims were in areas believed to be safe.Some victims were as far as 13 miles away.
30Krakatau erupted in 1883, in one of the largest eruptions in recent time The explosions were heard on Rodriguez Island, 4653 km distantAsh fell on Singapore 840 km to the N, Cocos (Keeling) Island 1155 km to the SW, and ships as far as 6076 km WNW. Darkness covered the Sunda Straits from 11 a.m. onthe 27th until dawn the next day.
31Giant waves reached heights of 40 m above sea level, devastating everything in their path and hurling ashore coral blocks weighing as much as 600 tonsAt least 36,417 people were killed, most by the giant sea waves, and 165 coastal villages were destroyed
32When the eruption ended only 1/3 of Krakatau, formerly 5x9 km, remained above sea level, and new islands of steaming pumice and ash lay to the north where the sea had been 36 m deep.
33Mount TamboraThe 1815 eruption of Tambora was the largest eruption in historic time.
34About 150 cubic kilometers of ash were erupted (about 150 times more than the 1980 eruption of Mount St. Helens).About 10,000 direct deaths were caused by bomb impacts, tephra fall, and pyroclastic flowsAn estimated 82,000 were killed indirectly by the eruption by starvation, disease, and hunger.
35Talcous dust was carried high into the stratosphere where it began to float around the earth. Due to this immense cloud of dust a part of the incoming sunlight was bounced back into space.
36“The Year Without a Summer” The 1815 eruption of Tambora caused the "Year without a Summer."Daily minimum temperatures were abnormally low in the northern hemisphere from late spring to early autumn.Famine was widespread because of crop failures.
37So, Are you feeling lucky So, Are you feeling lucky? Click the volcano below to go to the next slide.
38Quiz Index (Click on a button to select a topic) Plate Boundary QuizVolcano QuizReturn to homepageTo PowerPoint Index
39Convergent Boundaries Plate Boundary Quiz (Click on a button to choose a question about a boundary)Convergent BoundariesDivergent BoundariesCollisional BoundariesTransform BoundariesReturn to Index
40Volcano Quiz (Click on a button) Largest Eruption in Prehistoric Time?Largest Eruption in Modern Time?Smallest volcano “type”?Least explosive volcano “type”?Return to Index
41West Coast of South America Which is an example of a transform boundary? (Click the correct button)Coast of CaliforniaWest Coast of South AmericaHimalaya MountainsIcelandReturn to index
42West Coast of South America Which is an example of a divergent boundary? (Click the correct button)Coast of CaliforniaWest Coast of South AmericaHimalaya MountainsIcelandReturn to quiz index
43West Coast of South America Which is an example of a convergent boundary? (Click the correct button)Coast of CaliforniaWest Coast of South AmericaHimalaya MountainsIcelandReturn to quiz index
44West Coast of South America Which is an example of a collisional boundary? (Click the correct button)Coast of CaliforniaWest Coast of South AmericaHimalaya MountainsIcelandReturn to index
45Wrong Answer. (Did your fingers slip Wrong Answer! (Did your fingers slip?) Click the button below to try another question.Return to quiz index
46Fantastic!!! Way to go!!!! Click on the button below to go again! Return to quiz index
47What was the largest known eruption in prehistoric time What was the largest known eruption in prehistoric time? (Click on the correct button)KrakatoaYellowstoneMt. St. HelensVesuviusTamboraMt. PinatuboReturn to quiz index
48What was the largest eruption in modern (historic) time What was the largest eruption in modern (historic) time? (Click on the correct button)KrakatoaYellowstoneMt. St. HelensVesuviusTamboraMt. PinatuboReturn to quiz index
49Which of the below is the smallest type of volcano Which of the below is the smallest type of volcano? (Click on the correct button)Cinder coneShieldStrombolianCompositeReturn to Index
50Which of the below is the Least explosive Volcano “Type” Which of the below is the Least explosive Volcano “Type”? (Click on the correct button)Cinder coneShieldStrombolianCompositeReturn to Index