Volcanic eruptions

Describe pyroclastic material and lava flows

Introduction

There are two types of volcanic eruptions a quiet and explosive. Quiet eruptions have a low viscosity and gases can easily escape. Quiet eruptions are mostly made from mafic lava. Mafic lava is dark colored and made from magnesium and iron. When mafic lava cools it makes three types of lava flows. An explosive eruption has a high viscosity and has a large amount of trapped gases. Explosive eruptions shoot out pyroclastic material. Explosive eruptions are mostly made from felsic lava. Felsic lava is light colored and is made from feldspar and silica.

Types of magma

When mafic lava cools rapidly a crust forms on the surface of the flow. If it keeps flowing after the crust forms it wrinkles to form a volcanic rock called pahoehoe. Pahoehoe forms from hot fluid lava. As it cools it makes a smooth ropy texture. If the lava becomes to thick to form a wrinkly motion the surface breaks and forms jagged chunks to form another Type of magma called AA. AA lava texture results in differences in gas content and in the rate and slope of the flow of the lava. Blocky lava has a higher silica content than the AA lava. The high viscosity of the lava causes the cooled lava to break into lage chunks while the hot lava underneath continues to flow, this how it gives it a blocky texture.


Types of Pyroclastic Material

Pyroclastic material forms when magma breaks into fragments during an eruption, and when fragments of erupting lava cool and solidify as they fly through the air. Scientist classified the pyroclastic materials according to the size of the particles. Particles that are less than 2mm diameter are called volcanic ash. volcanic ash less than 0.25mm in diameter is called volcanic dust. Volcanic dust and ash settle on the land that surround the volcano. Large pyroclastic particles less than 64mm in diameter are called lapilli. Lapilli falls near the main vent. Lava spinning through the air cools and developed a round or spindle shape, this pyroclastic particle is called volcanic bombs. The largest pyroclastic particle is called volcanic blocks. Volcanic blocks are corned by solid rock blasted from the vent, some of the volcanic blocks are the size of houses.

videos

Lava flows
Amazing volcanic eruption video!