Presentation on theme: "VOLCANOES Lauren McCarthy. What is a Volcano? A volcano is an opening, or rupture, in a planet's surface or crust, which allows hot, molten rock, ash,"— Presentation transcript:
VOLCANOES Lauren McCarthy
What is a Volcano? A volcano is an opening, or rupture, in a planet's surface or crust, which allows hot, molten rock, ash, and gases to escape from below the surface. Volcanic activity involving the extrusion of rock tends to form mountains or features like mountains over a period of time. The 25 th Anniversary of Mt. St. Helens Eruption. pun.org/.../2005/05/25th-anniversar.htmlpun.org/.../2005/05/25th-anniversar.html
What are the Types? 4 Main Types: 1. A shield volcano has shallow-sloping sides. Shield volcanoes are formed by lava flows of low viscosity — lava that flows easily. Consequently, a volcanic mountain having a broad profile is built up over time by a flow after flow of relatively fluid basaltic lava issuing from vents or fissures on the surface of the volcano. Many of the largest volcanoes on Earth are shield volcanoes (All of the volcanoes in Hawaii). 2. A cinder cone is a steep conical hill of volcanic fragments that accumulate around and downhill from a and is usually active in eruption and is usually termed hot spot. The rock fragments, often called cinders or scoria, are glassy and contain numerous gas bubbles "frozen" into place as magma exploded into the air and then cooled quickly. Cinder cones range in size from tens to hundreds of meters tall. Mt. Presley located in New Avalon library.marist.edu/.../Mt.%20Presley.h tm Kilauea volcano in Hawaii.
Types Continued… 3. Composite volcanoes or 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 bases. Some of the most conspicuous and beautiful mountains in the world are composite volcanoes, including Mount Fuji in Japan, Mount Cotopaxi in Ecuador, Mount Shasta in California, Mount Hood in Oregon, and Mount St. Helens and Mount Rainier in Washington. 4. A lava dome or volcanic dome are formed by relatively small, bulbous masses of lava too viscous to flow any great distance; consequently, on extrusion, the lava piles over and around its vent. A dome grows largely by expansion from within. As it grows its outer surface cools and hardens, then shatters, spilling loose fragments down its sides. The Novarupta Dome formed during the 1912 eruption of Katma Volcano, Alaska. St. Augustine volcano, Alaska.
How do they Work? Volcanoes form when chambers of magma, or hot molten rock, boil to the surface. These magma chambers often remain sealed for hundreds of years between eruptions, until the pressure builds sufficiently to break through a vent, which is a crack or weak spot in the rock above. The blast creates a crater, where lava and ash spill out, forming the cone. On some volcanoes, the magma chamber collapses after a violent eruption and a caldera forms, which is just a large, bowl- shaped crater. Sometimes these calderas fill with water, as happened at Crater Lake in Oregon.
Where and How do they form? Most volcanoes are found along a belt, called the Ring of Fire, that encircles the Pacific Ocean. Volcanic activity also occurs in such places as Hawaii, Iceland, southern Europe, and at the bottom of the sea. Plate tectonics is the main reason for the formation of volcanoes.. Volcanoes can form when: Two plates collide- One of the plates is then forced under the other. As the plate sinks, friction and Earth's heat cause part of it to melt. This melted part then rises as magma. When it reaches the surface, it produces a volcano. Two plates spread apart- most such movement takes place on the ocean floor. As the plates move apart, magma below the crust moves up between the plates. Large amounts of lava pour onto the surface and build up the ocean floor. Magma sometimes creates an underwater mountain range, such as the huge Mid-Atlantic Ridge that runs down the length of the Atlantic Ocean. Magma Theory- Some scientists believe such volcanoes develop when a huge column of magma rises from inside Earth toward the surface. It comes close enough to the surface that it sometimes breaks through and forms a volcano. A number of volcanoes, for example those in Hawaii lie far from the plate boundaries. And this is where this theory come in.
Creation of Landforms There are four main land forms that can occur due to volcanoes: 1. Lava flows- is a (moving) outpouring of lava, which is created during a non-explosive effusive eruption; which forms igneous rock when it cools. 2. Volcanic Peaks- A volcanic peak is what we tend to think of when we talk about volcanoes. It is a volcano that has formed a large cone shaped hill, or mountain. These cones typically have a large bowl shaped crater in the top center. 3. Caldera- Calderas are massive crater-like depressions that can cover many tens of square miles. These calderas form when volcanoes explode with terrible destruction, completely obliterating the original volcano, and surrounding area. 4. Volcanic Neck- A volcanic neck is the remnant of an old volcano. As the volcano died, the last bit of lava inside of the volcanoes opening, or neck, cooled and hardened. Over many hundreds of thousands of years the material around the neck is removed by erosion, leaving only the harder neck behind.
A Caldera: Crater Lake Lava flow: Located in Hawaii Spewing lava 10 miles high. A Volcanic peak (located above) And a Volcanic neck (below). landforms.php