Types of volcanic eruptions

The five main types of volcanic eruptions and their characteristics, depending on the composition and viscosity of the magma. VIDEOGRAPHIC

Transcript

00:00Volcanic eruptions are categorized by volcanologists according to the composition of the magma,

00:11the very hot liquid rock which separates into lava and gas at the surface.

00:16If the magma is rich in basalt, it is very fluid.

00:19It rises easily in the volcano and spouts out in fountains of lava.

00:23The lava flows for long distances.

00:26As it solidifies, it becomes a volcano with a gentle slope, known as a shield volcano.

00:31If the magma also contains gas, the lava comes out in strips.

00:35The volcano also expels ash and rocks known as volcanic or lava bombs.

00:41These ejections accumulate closer to the crater and form a cone.

00:44If the magma is more viscous, it rises with more difficulty to the surface.

00:49It can remain blocked, like a cork, in the chimney of the volcano.

00:53Underneath, the pressure of the gases rises until the blockage is blown off.

00:57The resulting explosion ejects ash and more solid materials in a rising column several

01:03kilometers high.

01:04These types of eruptions release little lava.

01:07If the magma contains more silica, the lava is thicker and the pressure under the cap

01:11is even greater.

01:13When it gives way, the blockage is pulverized and the base of the dome is torn apart.

01:17A thick scorching cloud spurts out.

01:20This cloud of burning gas and lava hurtles down the side of the volcano at several hundred

01:26kilometers per hour.

01:27But there is an even more explosive type of eruption.

01:30This involves lava very rich in silica, which is put under so much pressure that when the

01:35cap blows, the volcano can itself collapse.

01:39The plume of ash which comes out of the volcano rises in the form of an umbrella cone, tens

01:44of kilometers high.

01:46Some of these eruptions are so violent they can modify the planet's climate for years

01:50to come.