Why did Mount St. Helens erupt?

What made mt st helens erupt!!!?

• I have a report 2 do over the holidays for geography!!!!!!!!!!!!!!!!!!

• Answer:

  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 eruption was preceded by a two-month series of earthquakes and steam-venting episodes, caused by an injection of magma at shallow depth below the volcano that created a huge bulge and a fracture system on Mount St. Helens' north slope. An earthquake at 8:32:17 a.m. on May 18, 1980 caused the entire weakened north face to slide away, suddenly exposing the partly molten, gas- and steam-rich rock in the volcano to lower pressure. The rock responded by exploding a hot mix of lava and pulverized older rock toward Spirit Lake so quickly that it overtook the avalanching north face. Some magmas contain a lot of volatiles (compounds that want tobe gases at low pressures). When a magma body intrudes inthe uppercrustandstarts tocrystallize, these volatiles come out of the liquidandwant to expand. In some cases, like in the case of mountst helens, the magma is covered by rockand the magma itself is too viscous,too thickflowing toletthese volatiles escape to surface. As a result, the gases cause the pressure to build, and eventually the pressure gets so great that it blows the coveroffofwhateveris keeping the gas from escaping, like a giant pressure cooker. Sometimes, the influxofgroundwaterfrom the surrounding rock adds to this, by converting to steam as it gets near the hot magma body. In any case, once the capping pressure is exceeded, the gas explodesoutward as fast as it can. If the cover was very solid and fought against this inside pressure for a long time, when it does blow, it really blows hard. At mountst helens, this blowout apparently occured sidewards rather than straight up, and thus a large area in one direction was smacked by the explosion, really really hard.