Question

D. GIVE REASONS FOR THE FOLLOWING
1. Some volcanoes erupt explosively.​

Answer 1

Answer:

What causes volcano to erupt?

Deep within the Earth it is so hot that some rocks slowly melt and become a thick flowing substance called magma. Since it is lighter than the solid rock around it, magma rises and collects in magma chambers. Eventually, some of the magma pushes through vents and fissures to the Earth's surface.

Explosive eruptions are favored by high gas content & high viscosity magmas (andesitic to rhyolitic magmas). The explosive bursting of bubbles fragments the magma into clots of liquid that cool as they fall through the air. These solid particles become pyroclasts or volcanic ash

Explosive eruptions

If a magma has a lot of gas which becomes trapped in the magma, the pressure will build and build until eventually the magma erupts explosively out of the volcano. ... Gas is trapped in the liquid, but if you shake the bottle the gas wants to escape.

Although there are several factors triggering a volcanic eruption, three predominate: the buoyancy of the magma, the pressure from the exsolved gases in the magma and the injection of a new batch of magma into an already filled magma chamber.

The two main factors that influence how a volcano will erupt are viscosity and gas content. Both are related to the composition of the magma . ... As the magma moves into the vent and the pressure drops, the gas wants to escape. The magma is very sticky and resists the expansion of the gas bubbles.

Answer 2

If a magma has a lot of gas which becomes trapped in the magma, the pressure will build and build until eventually the magma erupts explosively out of the volcano. It’s a bit like a bottle of fizzy soda. Gas is trapped in the liquid, but if you shake the bottle the gas wants to escape. This builds pressure inside the bottle, and when you release the pressure by opening the bottle, the gas rushes out the top carrying some of the liquid with it.

Phreatomagmatic eruptions are a type of explosive eruption that results from the magma erupting through water. The second phase of the Eyjafjallajökull eruption in 2010 was phreatomagmatic as a result of magma erupting under the ice. Some submarine volcanoes are phreatomagmatic, if the magma is gas-rich. For example Surtsey in Iceland. This eruption formed a new island.

Explosive eruptions can form pyroclastic flows which sweep down valleys destroying everything in their path. They also send ash high into the atmosphere forming plumes.