The explosive past of Mount Rainier volcano

The snow-capped stratovolcano Mount Rainier is reflected at sunrise in Tipsoo Lake near Chinook Pass. After a catastrophic eruption about 6000 years ago, the volcano grew to its present dimensions 2500 years ago and has since been intensively reshaped by glaciers.
Mount Rainier rises to an elevation of 4392 m (14410 ft). The stratovolcano itself is relatively young and exists for less than a million years although first volcanic activity in the Cascade Range begun already 40 million years ago. At that time the area was a shallow sea. The subduction of the oceanic Farallon Plate, which was a part of the Pacific Ocean plate, beneath the American continent ignited a young volcanic mountain range to rise above the sea level. Repeated lava flows and explosive volcanism piled up numerous rock layers. Additionally, large volumes of upwelling magma solidified underground forming a large pluton of coarse-grained granodiorite 12 million years ago. Erosion of the overlying mountains unroofed the pluton. The area glaciated in the Pleistocene Epoch while young Mt. Rainier began to form as a low and broad volcano on top of the mountainous terrain. Numerous eruptions lifted the volcano to lofty 4900 m (16.000 ft) about 75.000 years ago. One third of the mountain volume was rapidly eroded by glaciers. 6000 years ago, violent eruptions blasted away the eastern part of the mountain and the entire summit leaving behind a caldera that filled with ice. About 2500 years ago Mt. Rainier came into existence by reconstructing its summit with a new cone that the Native American Indians appropriately Tahoma, the mother of all waters. The last minor ash eruption occurred in 1850. Both rim craters are filled with several hundred feet of snow including a network of ice caverns and a pool of meltwater under the ice due to nearly boiling temperatures in the vents. Annual snow accumulation of about 100 ft (30 m) nourishes 26 glaciers.
Stratovolcanoes are composite volcanoes as they grow during short but violent eruptive events producing lava flows that alternate with pyroclastic eruptions of tephra causing ash fall and pumice. Relatively long phases of dormancy are followed by the next eruption cycle giving the volcano a layered structure. Mt. Rainier along with the Cascade Range volcanoes belongs to the Ring of Fire that encircles the Pacific Ocean. Volcanoes of that type usually contain intermediate to high silica magma resulting in explosive lava types called andestite and ryolihte. Silicate rich magma behaves like a thick paste and reduces the ability of gas to escape. This builds-up high pressure within the volcano that is suddenly released when the surrounding rocks break leading to explosive eruptions.