Volcanic Eruptions
Describe pyroclastic material and lava
What is Pyroclastic material?
Volcanic Dust
Volcanic ash that is less than 0.25 mm in diameter is called volcanic dust. Most volcanic dust and ash falls on the land and rapidly surrounds the volcanoe.
Volcanic Ash
Pyroclastic particles that are less than 2mm in diameter is called Volcanic ash.
Lapilli
Large pyroclastic particles that are less than 64mm in diameter are called Lapilli.
Volcanic Bombs
A volcanic bomb is a mass of molten rock. They are larger than 64mm in diameter and are formed when a volcano ejects violent amounts of lava. Once ejected they cool in stone type of rock before reaching land. Also, they can be thrown many kilometers when ejected from an erupting volcano.
Volcanic Blocks
A volcanic block is a big type of rock that measures more than 64mm in diameter. This rock is erupted in a solid condition and are made from the material left from the eruption before the present one. Volcanic blocks can also occur because of breakage of volcanic bombs. Also, the rocks can be enormous and can be erupted great distances from volcanic vents.
Cinder cones
A cinder cone is like a steep type of hill of volcano debris that all collects on top or downhill. The slope angles are of the cinder cones can approximately be up to 40 degrees. The slopes are not above a few 100 meters high. Cinder cones are formed from when volcanoes have really violent and explosive eruptions and are also made up of pyroclastic material.
Composite Volcanoes
Composite volcanoes are constructed of many layers of lava and ash. Composite volcanoes erupt very explosively and violently; that is because of the viscous magma . Also, when the viscous magma goes up , it clogs the crater hole and as a result pressure builds up and BOOM, a great eruption is created.
Shield Volcanoes
Shield Volcanoes are broad and domed volcanoes with gentle sloping sides. They are formed by hot fluid lava, and have shallow sides. They are often formed from basaltic lava. Shield volcanoes are a type of volcano that are commonly built almost entirely of fluid lava flows.
Strato Volcanoes
Strato Volcanoes are tall, conical and the volcano is made up of many layers of hardened lava, tephra, pumice, and volcanic ash. They are very much steep and have explosive eruptions. This volcanoes lava typically cools and hardens before spreading far because of its high viscosity. Also, this is among the most common types of volcanoes.
Types of Lava :
Pahoehoe
Pahoehoe is the least viscous type of mafic lava. It forms when mafic lava cools rapidly which then leads to a crust forming on top. If the lava continues to move then the crust will start to wrinkle. That wrinkly crust is the volcanic rock called the "Pahoehoe" .
Aa Lava
Aa lava is more viscous than the pahoehoe and forms sharp volcanic rock when it cools. If the crust forms weirdly or grows too thick to form wrinkles, the top will break into big,deformed, chunks called the "Aa Lava". The Aa forms from lava that has the same composition as the "Pahoehoe".
Blocky Lava
Blocky lava is the most viscous type of mafic lava and forms chunky volcanic rock when it cools. It has a greater silica content than the "Aa Lava". Since it has high viscosity it caused the the lava that cooled on top to break into big pieces.