Why did Mount St. Helens erupt so explosively?

Answer 1

The 1980 eruption resulted when a huge section of the mountaintop was forced outward and fell away from the mountain. The pressure of magma from within the mountain had been increasing over the years and the rock eventually gave way. With the blocking rock removed, huge amounts of hot rock, ash, and gas exploded from the opening with incredible force.
As part of the Cascade Range of mountains, Mount St. Helens was formed by eruptive flows of magma as the Juan de Fuca tectonic plate is forced under the North American Plate. Beginning about 37,600 years ago, periodic eruptions and magma flows occurred in the area between Mount St. Helens and Mount Rainer.
Huge eruptions occurred in the years 1480, 1482, and 1800, and smaller releases of steam between 1831 and 1857. The large magma chamber beneath Mount St. Helens will likely continue to force lava upward and cause future eruptions. However, as history indicates, they could be several hundred years apart.
The Mount St Helens eruption was like any other volcanic eruption: namely, the build up of pressure of magma and gas in the magma chamber beneath the surface.

The eruption was caused by the Juan de Fuca plate moving east, towards the North American plate. Because the Juan de Fuca is more dense, it was forced below the lighter North American plate. These movements caused friction, which then caused a rise in temperature, which melted the earth's crust. Then, because the magma from the mantle is less dense than the recently melted North American plate, the magma rose to the surface and caused the mountain to bulge (by about 1.5 meters a day). The pressure became so great that the mountain exploded sideways.
The one that triggered the 1980 eruption of Mount St. Helens was the 5.1 earthquake that created the landslide.The dome that was bulging on the west side of the volcano also triggered the eruption.

Mt St Helens erupted due to pyroclastic flow. There was a huge blister on the north face of the mountain that grew up to 5ft a day until an earthquake took place which caused a land slide. The landslide was one of the biggest ever to be recorded and managed to pop the bulge, by Nii Lomotey Engmann.

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A volcano does not erupt because it produces any given form of lava! A pyroclastic flow is one form of eruption, not its cause. The America's (N and S) volcanoes are a consequence of the Pacific Ocean closing.

Answer 2

The pressure had been building in a magma chamber under the mountain, at least partly due to surface water seeping down into cracks and building up superheated steam.

When the unstable north face of the mountain slid off, this pressurized material pushed to the surface with sudden and unstoppable force, and formed an expanding column of hot ash that carried 80,000 feet into the air. The ash was mostly silicon dioxide and aluminum oxide, relatively light by volcanic standards.

Answer 3

Because there was to much poo cloged up in the volcano so it all burt out like diareh