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Hots" are places where a chamber of magma has accumulated at depth beneath the surface. The volcanic islands of Hawaii are a notable example of this. The Hawaiian Islands ride atop the Pacific plate as it moves in a northwesterly direction over the hot spot that creates the volcanoes. Therefore, the oldest volcanic island is found at the northwest end of the chain and the youngest to the southeast. Volcanic activity ceases as the older islands move off the hot spot. Next
Figure 16. 7 Lava fountain of the Pu`u `O`o cinder and spatter cone on Kilauea Volcano, Hawaii. Source: USGS Used with permission Rather than forming a mountain like the volcanoes in the Hawaiian Islands, some places have been covered by massive flows of basaltic lava due to volcanic activity. One of the best known sites in North America is the Columbia Plateau. The Columbia Plateau is located in the eastern Washington, south through eastern Oregon and most of southern Idaho. Assess your basic understanding of the preceding material by"Looking Back at Volcanic Features and Distribution" or continue reading. {{ Activity
Distribution of volcanic activity Volcanic activity is widespread over the earth, but tends to be concentrated in specific locations. Volcanoes are most likely to occur along the margins oftectonic plates, especially in subduction zones where oceanic plates dive under continental plates. As the oceanic plate subducts beneath the surface, intense heat and pressure melts the rock. Molten rock material, magma, can then ooze its way toward the surface where it accumulates at the surface to create a volcano. Volcanic activity can be found along theMid-ocean ridge systemas well. Here, oceanic plates are diverging and magma spreads across the ocean floor, ultimately being exposed at the surface. Crustal spreading long the ridge is partly responsible for the volcanic activity of Iceland. It is also thought that a "hot spot" lies beneath the island that contributes to volcanism. Next
Mr. Mohammad Ashraf • Mr. ArshidHussain • Mr. AbMajeed • Mr. Assad Ullah. • Mohammad Maqbool
INTRODUCTION Objectives • The earth has mainly three layers i.e crest, mantle and core. The upper most layer of the earth is known as crest. This part of layer is fertile and contains minerals. Below this layer is mantle about 35km from beanth crest. The inner most layer i.e. core is very hot. Its temperature raises to 10000 ˚c. The bursting out of molted rocks and gases from the crystal rock base up words through vents are called Volcanoes. They travel up to the surface with their great force and burst out through openings called craters.
OBJECTIVES Contents • To provide ample information about the volcanoes. • To aware the learners about disasters through volcanoes. • To prepare them how to make safety during this hectic period.
CONTENTS Volcanoes VIDEO Types
Types Volcanoes come under the category of natural calamities . Man has no control over them neither have predictions . Volcanoes when they erupt destroy life and property on a large scale. The word volcano derived from volcano, one of the volcanic lipari islands in the meditation sea, and the place where ,according to Roman mythology , vulcan ,gGod of fire kept his forge. We know that the sun is burning star and the planet earth is a part of it. When the earth got saperated from the sunit also was burning. Gradually it cooled down on the surface but internally it is still burning inferno. Volcano spread it solid matter, liquid matter as well as gasses . The solid matter thrown out consists of local pieces of blasts rocks. The molten rocks sttot out into the sky. But the time it comes down it cools and becomes solid. The solid pieces are called cinde3rs. The liquid matter that is ejected out by the volcano is called magnet. As soon as it comes out of volcanoes it is called Lava. Its temperature is very high. It appears red and white when it is hot. And turns black after it cools. Lava destroys by burning every thing thast comes in its way. The city of Pompey is a good example of the Lava flow. . Then there is a third one, gasses materials steam is the major part of material gas water mixed with magma is also ejected along with steam. This water is called Juvenile water.
Evaluation • Objective type questions: • Magma and gases exploit weak zones in the earths ………. Layer. • Inner most b. Outer most • Most of the world’s volcanism there fore takes place ………beneath the oceans. • Seen b. unseen • 3. Most volcanic activity occurs along tectonic plate boundaries where the lithosphere is……… • a. Hardest b. weakest Contd
4. Magma and gases exploit…. Zones in the earth’s crust. Weak b. strong 5. Shield volcanoes have relatively gentle slopes generally of ………………….. Less than 12 ⁰ b. greater than 12⁰ 6. North of manila erupted in June & july 1991 b. august 1991 Hawiian island volcano is ….. Type of volcano Shield b. caldera There are……types of volcanoes. a. Three b. five
Video Shield Tephra When tephra, solid materials ejected into the air during an eruption, erupts from a vent and descends back to the earth, it creates cinder cones. The tephra forms a cone-shaped mountain. Western Mexico’s Paricutin is a well-known cinder-cone volcano. When tephra and lava erupt from a vent that is central, it creates composite volcanoes. Around a towering, cone-shaped mountain, the materials pile in alternate layers behind the vent.
Video Distribution Shield Volcano Volcanoes have been divided into three main groups by scientists. They are shield volcanoes, cinder cones, and composite volcanoes. The material of the volcano as well as the shape define these groups. When a large amount of free-flowing lava spills from a vent and spreads along a large area, it creates shield volcanoes. The lava slowly builds a broad, low, dome shaped mountain. Mauna Loa is a shield volcano.
Caldera Tephra Volcano Sheild Volcano
