Volcanic Eruptions
Describe the Pyroclastic Material and Magma
What is Pyroclastic Material?
Some Pyroclastic
Material forms when magma breaks into fragments during an eruption because of the rapidly expanding gases in the magma.
What are the different types of Lava?
Pahoehoe lava
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 is the least viscous type of mafic lava. It forms wrinkly volcanic rock when it cools. Pahoehoe forms from hot, fluid lava. As it cools, it forms a smooth, ropey texture. Pahoehoe actually means "ropy" in Hawaiian.
Aa Lava
If the crust deforms rapidly or grows too thick to form wrinkles, the surface breaks into jagged chunks to form Aa lava. Aa lava is more viscous than pahoehoe lava and forms sharp volcanic rock when it cools. 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 is the most viscous type of mafic lava and forms chunky volcanic rock when it cools. Blocky lava has. Higher silica content than as lava does, which makes blocky lava more viscous than Aa lava. The high viscosity causes the cooled lava at the surface to break into large chunks, while the hot lava underneath continues to flow. This process gives the lava flow a Blocky Appearance.
What are the three different types of Volcanoes?
Shield Volcano
Volcanic cones that are broad at the base 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.
Cinder Cone Volcano
A type of Volcano that has very steep slopes is a Cinder Cone. The Cinder Cones form from explosive eruptions and are made of Pyroclastic Material. The slope angles of the cinder cone can be close to 40, and the slopes are rarely more than a few hundred meters high.
Composite Volcano
Composite Volcanoes are made 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.