Volcanic eruption
Describe the Pyroclastic material and magma
What is Pyroclastic material?
Volcanic ash and volcanic dust
Pyroclastic particles that are less than 2 mm in diameter is called volcanic ash. Volcanic Ash that is less than 0.25 mm in diameter is called volcanic dust. Most volcanic dust and ash settles on the land that immediately surrounds the volcano.
Lapilli
Large Pyroclastic particles that are less than 64 mm in diameter, are called lapilli, which is from a Latin word that means " little stones". Lapilli generally fall near the vent.
Volcanic blocks and volcanic bombs
Large clots of lava may be thrown out of an eruption volcano while they are red-hot. As they spin through out the air, they cool and develop a round or spindle shape. These Pyroclastic particles are called volcanic bombs. The largest Pyroclastic materials, known as volcanic blocks, form solid rock that is blasted from the vent. Some volcanic blocks are the size of a small.
Lava flows
Pahoehoe
When mafic lava cools rapidly, a crust forms on the surface of the flow. If the lava continues to flow after the crust forms, the crust wrinkles to form a volcanic rock called pahoehoe. Pahoehoe forms from hot, fluid lava. As it cools, it forms a smooth, ropy texture. Pahoehoe actually means "ropy" in Hawaiian.
Aa
If the crust deforms rapidly or grows too thick to form wrinkles, the surface breaks into jagged chunks to form Aa. Aa forms from lava that has the same composition as pahoehoe lava. Aa lava's texture results from differences in gas content and in the rate. And slope of the lava flow.
Blocky lava
Blocky lava has a higher silica content than Aa lava does which makes blocky lava more viscous than Aa lava. The high viscosity causes the cooled lava at the surface to break into chunks, while the hot lava underneath continues to flow. This process gives the lava flow a blocky appearance.
Types of volcanoes
Shield volcanoes
Volcanic cones that are that are broad a the base and have gently sloping sides are called shield volcanoes. A shield volcano covers a wide area and generally forms from quiet eruptions. Layers of hot, mafic lava flow out around the vent, harden, and slowly build up to form the cone. The Hawaiian island form a chain of shield volcanoes that built up from the ocean floor at a hot a hot spot, example the Hawaiian islands.
Cinder cones
A type of volcano that has very steep slopes is a cinder cone. The slope angles of the cinder cones can be close to 40 degrees, and the slopes are rarely more than a few hundred meters high. Cinder cones form from explosive eruptions and are made of Pyroclastic material.
Composite volcanoes
Composite volcanoes are mad of alternating layers of hardened lava flows and Pyroclastic material. During a quiet eruption, lava flows cover the sides of the cone. Then, when an explosive eruption occurs, large amounts of Pyroclastic material are deposited around the vent. The explosive eruption is followed again by quiet lava flows. Composite volcanoes, also known as stratovolcanoes, commonly develop to form large volcanic mountains.