Products of Volcanoes Lava & Lava Flows In most eruptions, lava flows out of vents as a red hot stream of molten rock with it's temperature at about 2000 degrees fehrenheit. When cooling begins, the very top of the lava turns a silvery blue color while the inside stays red. Some lavas flow freely, and are very fluid-like, while others are viscous, and flow slowly. Rhyolite lavas are sticky, very slow moving lavas, containing large amounts of silica, sodium, potassium, and aluminum. They can get so thick, that they hardly flow at all. These lavas could eventually form a steep sided hill, called a volcanic dome. Rhyolite lava sometimes squeezes through breaks in the dome and hardens into sharp spines. Basalt lavas are fast moving fluid lavas and contain about 50 pecent silica along with smaller amounts of aluminum, iron, magnesium and calcium. These lavas can travel very far due to their fluidity. When they harden, they form huge plateaus. Igneous Rock Igneous rock is formed when magma becomes solid. One type is granite, while another is obsidian. Granite froms when magma cools below the surface of the earth. Obsidian forms from erupted magma on the earth's surface. Volcanic Fragments During eruptions, lava is thrown into the air and torn into small framents. The solid materials thrown, are known as pyroclastics-or fire broken in Greek. Scoria is also produced. When it is full of gas bubbles, it is called pumice. It can be light enough to float on water. However, most of the material thrown out of the volcano is just volcanic ash, smaller than two tenths of an inch in size. A hard rock called tuff is formed when loose volcanic ash is cemented together. Large, unusually shaped solid fragments are colled blocks. Fragments of a medium size are called lapilli. Heat & Gas Enormous amounts of heat are released during a volcano's life. Most of the heat escapes into the air, but in some volcanic regions, the heat remains in the ground. The heat stored under ground, is a natural form of energy known as geothermal energy. The regions containing the geothermal energy often have natural springs releasing fountains of hot water and steam. During an eruption, gas is also released carrying ash and rock fragments. Steam and carbon dioxide is the majority of the gas released. Another common gas produced is sulfur dioxide which has a strong, sometimes suffocating odor. Types of Volcanoes Shield Volcanoes Cinder Cones
~The Formation of Volcanoes~
Though millions of years are needed for natural forces to erode canyons and build up many mountain ranges, an erupting volcano can destroy large buildings, even cities, in a matter of only minutes or days. Volcanic activity is the quickest and most devestating of all natural occurences that shape the earth's surface.
~ The escape of the earth's interior heat, along with the heat given off by decaying radio-active elements, provide the heat for volcanic activity.
~ As the heat rises, the rock located in the eath's interior is heated and begins to slowly move toward the surface. This molten rock is known as magma.
~The magma gradually cools within the earth, but sometimes makes its way upward.
~ Even though heat causes the magma to rise to the surface, the escaping gases are what provide the force for volcanic eruptions- the most common being steam.
~ The now gas filled magma rises from the earths interior and collects in large pools, called magma chambers. These can be several miles below the surface.
~ When the amount of gases increases, the magma gets to be lighter, which causes it to rise through a system of channels called conduits.
~ When the magma finally reaches the surface, it shoots out of vents, or openings, at the top of the conduits.
~ When magma erupts from a vent, it becomes known as lava. This lava, along with ash and rock, eventually build up to form the cone of the volcano.
Pahoehoe and aa are two common types of lava flows. Pahoehoe lava has a smooth rolling surface that wrinkles and looks like the coils of rope. When it erupts from an underwater volcano, it often forms pillow lava because it looks just like a pile of pillows. On the other hand, aa lava has a very rough surface with several jagged fragments in it. When it is moving, it looks like blocks tumbling over one another.
Stratovolcanoes
