Mount Hood formed as a stratovolcano from layers of lava flows, ash from the air and volcanic mudflows. Its primary construction is from a family of rocks known as andesite. The initial volcano formed more than 500,000 years ago, and it has seen long periods of inactivity followed by short periods of activity that formed the mountain.Know More
The National Science Foundation reports that two types of magma mixed a few weeks before each of Mount Hood's historic eruptions. This mixing is unlike what occurs in many other stratovolcanos, even those within the same Cascade Range as Mount Hood, like Mount St. Helens, only 60 miles away. Mixing the two lava types causes the pressure to build, causing an eruption, but it is usually less violent than the eruptions of other volcanoes. This same mixing provides the ingredients required for formation of andesite, leading scientists to believe Mount Hood formed in the same way as other andesite volcanoes.
While eruptions built the base of Mount Hood, weathering and erosion have formed the visible mountain. The movement of glaciers from the top of the mountain helps to break down the rock that forms its shape. These movements break through lava domes to allow new flow to escape.
While scientists consider Mount Hood an active volcano, they expect its next eruptions to include small lava flows. Models indicate an eruption is not likely to cause major damage in Portland, Ore., only 45 miles away.Learn more about Geology
Graphite is a polymorph of carbon typically formed through the metamorphism of organic material found in mineral deposits. It can also appear during the formation of igneous rocks or as nodules inside of iron meteorites.Full Answer >
Gabbro, a type of intrusive igneous rock, is formed when magma cools and solidifies inside the crust of the Earth. Because it cools slowly, it is coarsely grained.Full Answer >
Sand is formed by the erosion of rocks, which become tiny particles. These tiny particles are picked up by wind and water and become sand.Full Answer >
Chert is most often created when microcrystals of silicon dioxide are formed within soft sediments that over time will turn into chalk or limestone. When large amounts of silicon dioxide microcrystals are present in the sediment, they start to clump together and can eventually form whole layers of chert within a limestone deposit.Full Answer >