A volcano is a vent in the earth which gases and molten rock (melted rock, otherwise known as magma) are forced through up onto the surface of the earth, due to high pressure.
Magma is molten rock below the surface of the earth, and lava is what magma is called after it erupts onto (above) the surface of the earth. The terms below and above are bold to emphasize the importance of the molten rock’s location.
The volcanic mountains observed (which people usually refer to as volcanoes) are actually cooled lava and ash which came from past eruptions. Lava becomes solid rock when cooled. Lava is molten (melted) rock.
Over extended time periods, each successive eruption deposits more lava on top of the existing rock, and then it cools as well. So with each eruption, another layer of rock is deposited on top of the old one and cools until a mountain is formed.
Simply put: Lava keeps flowing out, cools to become solid rock, and then that same process is repeated later on top of that rock until it becomes a mountain.
Note that all volcanoes are tall cone-shaped mountains. There are also shield volcanoes with gentle slopes (they look like a shield on the ground), stratovolcanoes (these resemble mountains), cinder cone volcanoes with a crater at the top, among others.
Some volcanoes (such as Yellowstone) do not protrude noticeably above ground and may have just a caldera above ground.
Volcanic Hazards
There are multiple volcanic hazards, some of which may surprise you, such as:
- Volcanic Ash: This consists of very hard and abrasive fragments of volcanic glass, minerals, and rock which can cause lung cancer and choking. These fragments are less than 2mm in diameter. As you would expect, the smallest ash particles travel and fall the furthest distance from the erupting volcano, and the largest ones fall nearest to the volcano due to their heavier weight. [Source].
- Sulfur Dioxide (SO2) and Carbon Monoxide (CO): These substances are highly toxic.
- Lava: Lava is 700 (1,292 °F) to 1,200 °C (2,192 °F) [Source]. It is therefore hot enough to cause serious injury or even be fatal if you get your foot stuck in it, for example. Large scale lava flows can wipe out an entire village, not only because it will burn it, but it is also extremely heavy and viscous (dense and syrupy).
Volcanic Eruption Types
Effusive Eruptions
Effusive volcanic eruptions are characterized by a steady flow of lava out of the volcano’s vents. Two well-known examples of volcanoes with predominantly effusive eruptions are Kilauea in Hawaii and Bardarbunga in Iceland.
Effusive eruptions tend to pose a smaller threat to nearby residents due to their slower, steadier nature that provides them with a warning in advance. Significant damage to permanent infrastructure may still occur. However, people evacuate if they are too close to the eruption.
There are both low viscosity and high viscosity effusive eruptions. High viscosity eruptions produce thick, slow-moving and viscous lava. Low-viscosity eruptions produce runny lava that flows faster (for example: lava rivers produced by Kilauea in Hawaii as well as Bardarbunga in Iceland).
Explosive Eruptions
Explosive volcanic eruptions are sudden and violent. This type of eruption causes the most fatalities for multiple reasons.
Explosive eruptions launch fragments of hot rock, magma and ash at speeds exceeding 60 mph, and up to 450 mph. This means that humans are unable to outrun these eruptions if they are too close.
Explosive eruptions can cause pyroclastic flows, eruption columns (blasting material upwards), and avalanches. Pyroclastic flows are high-speed downhill flows of rock fragments and ash that are known to engulf towns, trap people and cause death by burning.
Super Eruptions
Volcanic super eruptions are caused by supervolcanoes (for example: Yellowstone). These eruptions are significantly larger than all other eruptions. Super eruptions are exceedingly rare, potentially extinction-level events.