Volcanic Eruptions
Describe pyroclastic materials and lava.
What is pyroclastic material?
Pyroclastic Material
Some pyroclastic materials form when magma breaks into fragments during an eruption. Other form when fragments of erupting lava cool and solidify. Scientist classify pyroclastic materials according to their sizes.
Pyroclastic particles that are less than 2mm in diameter are volcanic ash. Volcanic ash that is less than 0.25mm in diameters is called volcanic dust. Large pyroclastic particles that are less than 64mm in diameter are called lapilii. Large clots of lava may be thrown out of an rut piling volcano. As they spin through the air they cool and develops round or single shape. These pyroclastic materials are called volcanic bombs. The largest pyroclastic materials are known as blocks they form from solid rock that is blasted from the vent. Felsic lava tends to explode and throw Pyroclastic material into the air.. Felsic lavas of continental volcanoes, such as Mount St. Helens, tend to be more cooler and stickier. Felsic lava is contains Silica and Feldspar. Felsic lava contain large amounts of trapped gases, such as water vapor and carbon dioxide. When a volcano erupts the gases within the lava escape and send molten and solid particles into the air. It throws pyroclastic materials into the air. It also is light-colored and has a a high viscosity.
Pyroclastic material are classified according to the size of the particles
Volcanic ash or Volcanic dust.
Volcanic ash is 2mm in diameter. Volcanic ash that is less than 0.25 mm in diameter is volcanic dust. Most volcanic ash and dust settles on the land that immediately surrounds the volcano. Some of the smallest dust particles travel around the world in the upper atmosphere.
Lapilli
Large pyroclastic particles that are less than 64mm in diameter are called lapilii it's from a Latin word (means "little stones") lapilii fall near the vent.
Volcanic Bombs& Volcanic Blocks
Large clots of lava are thrown out of an erupting volcano while they are hot. As they spin through the air they cool and develop a spindle shape. These pyroclastic particles are known as volcanic bombs. Volcanic blocks are the largest pyroclastic materials they form from solid rock that is blasted from the vent. Volcanic blocks can be as large as a small house.
Types Of Lava
Types of lava
Mafic magma has a low viscosity meaning the lava moves much slower. It contains magnesium and Iron. It has less trapped gases and is dark in color. Mafic lava causes quiet eruptions.
Pahoehoe
Pahoehoe is the least viscous type of Mafic lava. It forms wrinkly volcanic rock when it cools.
Aa
Aa lava is more viscous than pahoehoe lava and forms sharp volcanic rock when it cools.
Blocky Lava
Blocky lava is thick vicious lava that does not travel far front the erupting vent. It forms chunky volcanic rock when it cools.
Three Types Of Volcanoes
Shield Volcanoes,Cinder Cones, and Composite Volcanoes.
Shield Volcanoes are broad at the base and have gently sloping sides. It covers a wide area and generally forms quiet eruptions. Layers of hot,Mafic lava flows out around the vent and hardens.Cinder Cones has very steep slopes. The slope angles of the cinder cones can be 40,and are rarely more than a 100 meters high. Cinder ones form from explosive eruptions and are made of pyroclastic material. Composite Volcanoes are made of alternating layers of hardened lava flows and pyroclastic material. Composite volcanoes have both quiet and explosive eruptions.
Shield Volcano ( Mount Okmok)
Mt. Okmok is a shield volcano. Mount Okmok is the highest point on the rim of Okmok Caldera. It forms quiet eruptions. Shield volcanoes are usually built of low viscosity basaltic lava's that erupt in longer cycles than that of a Strato volcano.
Cinder cones Tolmachev Dol
Tolmachev Dol is located in Russia.The cones and lava fields cover a broad area on both sides of scenic Lake Tolmachev, which lies in large depression halfway between Opala and Gorely volcanoes.The latest dated eruption at Tolmachev Dol occurred from a cinder cone in the NW part of the plateau about 1600-1700 years ago.
Composite Volcano Mt. saint Helen's
Mt. Saint Helen's is a composite or "Strato" volcano. It produces both quiet and explosive eruptions.