What type is a stratovolcano

Hot magma rises because it is less dense than the surrounding rock. Trapped gases in the magma also force it upwards. Not to scale. Where a volcano produces low viscosity, runny lava, it spreads far from the source and forms a volcano with gentle slopes: a shield volcano. Most shield volcanoes are formed from fluid, basaltic lava flows.

Mauna Kea and Mauna Loa are shield volcanoes. Stratovolcanoes have relatively steep sides and are more cone-shaped than shield volcanoes. They are formed from viscous, sticky lava that does not flow easily.

The lava therefore builds up around the vent forming a volcano with steep sides. Stratovolcanoes are more likely to produce explosive eruptions due to gas building up in the viscous magma. Andesite named after the Andes Mountains , is perhaps the most common rock type of stratovolcanoes, but stratovolcanoes also erupt a wide range of different rocks in different tectonic settings.

Stratovolcanoes, also known as composite cone volcanoes, erupt viscous lava that forms a steep-sided, triangular-shaped structure. Its last known eruption was in The low afternoon sun emphasises the conical shape of the volcano. As viscous lava is not very fluid, it cannot flow away from the vent easily when it is extruded.

Instead it piles up on top of the vent forming a large, dome-shaped mass of material. Magma is stored beneath a volcano in a magma chamber.

The exact composition of a cinder cone depends on the composition of the lava ejected from the Earth. In certain areas of the world, huge calderas have been found to be the remains of volcanic eruptions of enormous scale Figure 8.

These calderas are volcanic features that are formed by the collapse of a huge amount of land due to the powerful eruptions. Caldera comes from Latin word, meaning cauldron.

Calderas are generally circular shaped geographic formations like the picture in figure 6. These are not singular mountains but entire geographical areas. Yellowstone National Park in Wyoming is another caldera that has blown about a hundred times in the last 16 million years. Supervolcanoes represent the most dangerous type of volcano. An eruption from a supervolcano could change life on Earth as we know it for many years. Supervolcanoes were not even accepted in volcanology until this millennium.

Many supervolcano eruptions are thought to have occurred, the most recent in New Zealand less than years ago. That explosion was thought to have ejected about cubic kilometers of material. A supervolcano eruption near what is now Colorado was thought to have let loose over 5, cubic kilometers of material millions of years ago.

In comparison, the Mt. Saint Helens eruption ejected about 1 cubic kilometer of material. The eruptions from supervolcanoes can be so large that the ash ejected into the air blocks the Sun and lowers the temperature on the entire planet.

The lowered temperatures caused by these eruptions is called a volcanic winter. One can only imagine how such a huge eruption would change the world in modern times.

The largest supervolcano in North America is the Yellowstone caldera, which had three super eruptions at 2. Long Valley caldera, south of Mono Lake in California, is the second largest supervolcano in North America, erupting extremely hot and explosive rhyolite around , years ago. An earthquake swarm in alerted geologists to the possibility of another eruption in the future, but the timing of such an event is unknown.

Supervolcanoes are a fairly new idea so the exact cause of supervolcano eruptions is still debated. However, scientists believe that an entire and very large magma chamber erupts in a catastrophic explosion. This enormous eruption creates a huge hole or caldera where the surface area collapses. Skip to main content. Search for:. If you really want to get your hands dirty and dive into volcanoes figuratively , the fun starts here. If you want to understand volcanoes, you have to understand plate tectonics.

The surface of our planet is not one big piece — it is broken into 17 major, rigid tectonic plates, that move one in relationship to the other. Volcanoes on Earth are generally located in areas where the tectonic plates diverge or converge with each other. Examples of hotspots include Hawaii and the Portuguese island of Madeira, but for the most part, volcanoes lie at the edge of tectonic plates. OK, so now we know that volcanoes form where the magma can rise up to the surface, which leads us to the next question:.

The key word here is buoyancy. Magma is very hot, and therefore less dense than the surrounding rocks; it simply rises due to a difference in buoyancy. This lighter magma rises toward the surface, and when its density is lower than the surrounding rocks, it flows towards the surface. But when the magma reaches the surfaces, another interesting thing happens. This tends to happen a lot of the magma is more acidic has a higher silica content ; with more basic magmas, there is usually a continuous, steady flow like in Hawaii.

Stratovolcanoes consist of many layers strata of hardened lava, tephra, pumice, and volcanic ash. They generally have steep slopes and are the most common type of volcanoes on Earth. They tend to form at subduction zones where one tectonic plate is sliding beneath the other — the oceanic plate beneath the continental plate.

Their eruptions are typically explosive and effusive ; the magma is generally rich in volatiles because the magma rises as water trapped both in hydrated minerals and porous basalt rock of the upper oceanic crust is released into mantle rock of the asthenosphere above the sinking oceanic slab.

This release of water pushes the magma towards the surface. The chemical composition of the magma is intermediate because it incorporates both basic from the oceanic plate and acidic minerals from the continental plate.