1 Mt. Etna, Sicily

2 Parts of a Volcano

3 Volcano Cross-section

4 Calderas Created when a magma chamber is emptied, and the rock above collapses back into the empty chamber, causing a large depression in the ground, which often fill up with water. Crater Lake Caldera

5 Calderas Photograph by M. Williams, National Park Service, 1977 Aniakchak Caldera

6 How Volcanoes Form

7 Plate Tectonics Volcanoes can be located in one of three locations: 1) A convergent plate boundary 2) A divergent plate boundary 3) A hotspot

8 Convergent Boundaries Plates converge, and one slides underneath the other; oceanic crust is destroyed

9 Divergent Boundaries Photography courtesy of Woods Hole OceanographicWoods Hole Oceanographic InstitutionInstitution and members of the Adventure dive About 2.4 mi 3 of crust is created this way All divergent boundaries are in the middle of the ocean at mid-ocean spreading centers

10 Hot Spots Hawaii is the most famous chain of islands created by hotspot activity The plate slides over the hotspot, creating volcanoes in a chain

11 How Volcanoes Form Weaknesses exist at these boundaries Magma lighter than surrounding rock Finds a weakness and pushes upwards to the surface, causing a volcano Sketch by B. Myers

12 Volcano Products

13 Lava Photograph by J.D. Griggs on 13 November 1985 Lava flowing on Kilauea Volcano, Hawaii

14 Pahoehoe Is Basaltic lava with a ropy, smooth or bumpy surface texture

15 Gases Mainly water, carbon dioxide, and sulfur dioxide Toxic gases include hydrogen sulfide (rotten egg gas), sulfuric acid, and Hydrochloric acid Photograph by K.A. McGee on 19 September 1995 Gases from Pu`u `O`o vent on Kilauea Volcano, Hawaii

16 Tephra: Ash Photograph by D.E. Wieprecht Must be smaller than 2 mm in diameter Commonly less than mm in Diameter Does not dissolve in water

17 Tephra: Lapilli Lapilli from the summit of Kilauea Volcano in 1959

18 Blocks and Bombs Photograph by J.P. Lockwood on July 10, 1982 Photograph by C. Heliker on January 26, 1988

19 Pyroclastic Flows Photograph by C. Newhall on 15 September 1984 Are dangerous movements of ash, rock fragments, pumice and gas Move very rapidly: up to 65 mph!! Usually more than F! Pyroclastic flows are far and away the most deadly volcanic occurrences. If you see one, get as far away as fast as possible!!!

20 Lahars Volcanic mudflows, composed of volcanic material, water, mud, and anything else available Photograph by J.N. Marso on 14 August 1989 Guatemala

21 Types of Volcanoes

22 Cinder Cone Volcanoes They are the most common type, yet are the smallest type as well Have the steepest sides of the three types, and the largest summit craters Responsible for 648 / 1,511 of known eruptions over the past 10,000 years [42.9%]

23 Cinder Cone Volcanoes Aerial view looking west to Sunset Crater. Photography by Wendell Duffield, U.S. Geological Survey Sunset Crater. Photograph courtesy of the National Park Service.

24 Cinder Cone Volcanoes Photograph by J.P. Lockwood on 1 December 1975 Pu`u ka Pele

25 Shield Volcanoes They are very wide, broad volcanoes The magma that is released flows very easily, which creates their wide profile Responsible for 164 / 1511of known eruptions over the past 10,000 years [10.8%]

26 Shield Volcanoes View of the NNW flank of Mauna Loa Volcano from the south side of Mauna Kea Volcano, Hawaii; both are shield volcanoes.

27 Shield Volcanoes Three-dimensional Space Shuttle Image of the Alcedo Shield Volcano, Galapagos. Courtesy of JPL/NASA.

28 Stratovolcanoes Also known as composite volcanoes Are the “most picturesque”, but also the most deadly because of the material they eject Have gentle lower slopes, and steep upper Slopes Not the most common, but are most famous because of deadliness Responsible for 699 / 1,511 of known eruptions over the past 10,000 years [46.3%]

29 Stratovolcanoes Photograph by R. McGimsey on 15 July 1990 Mount Mageik, Alaska

30 Other Important Stratovolcanoes Mt. St, Helens, Washington. A view to the north of the "two tone" mountain - an appearance produced by prevailing easterly winds during the initial activity of Mount St. Helens. Photo by C. Dan Miller

31 Other Important Stratovolcanoes Mt. Fuji, Japan

32 Mt. St. Helens, 1980 Courtesy of Don Swanson, USGS  Steam was seen rising out Helens in this April 10, 1980 picture

33 Mt. St. Helens, 1980   Shown is the “bulge” in the Side on April 27,1980  The “bulge” had expanded more than 100 meters out!!!  Notice how large the “bulge” grew from only April 10 to April 27!

34 Mt. St. Helens, 1980 Courtesy of USGS.   Rose to a height of more than 20 kilometers!!  Lasted more than 9 Hours  Ash was carried as far away as the great plains

35 References Most images from USGS : Most information and data from: