By the end of this lesson, you'll know
The Eruption of Mount St. Helens in 1980
A volcano refers to a rupture in the crust of a planetary object like Earth, allowing hot lava, gases, and volcanic ash to escape from below the surface in the magma chamber. When pressure builds up, eruptions occur. Gases and rock shoot up through the opening and spill over or fill the air with lava fragments. Eruptions can cause lateral blasts, lava flows, hot ash flows, mudslides, avalanches, falling ash, and floods. Volcano eruptions have been known to knock down entire forests. An erupting volcano can trigger tsunamis, flash floods, earthquakes, mudflows, and rockfalls.
A light, porous volcanic rock that forms during explosive eruptions is known as pumice. It resembles a sponge because it consists of a network of gas bubbles frozen amidst fragile volcanic glass and minerals. All types of magma (basalt, andesite, dacite, and rhyolite) will form pumice.
The Pacific Ring of Fire is an area of frequent earthquakes and volcanic eruptions encircling the basin of the Pacific Ocean. The Ring of Fire has 452 volcanoes and is home to over 50% of the world’s active and dormant volcanoes. 90% of the world’s earthquakes and 81% of the world’s largest earthquakes occur along the Ring of Fire.
The volcanoes of the Earth are said to occur due to the fact that its crust is broken into 17 main, rigid tectonic plates floating on a softer and hotter layer in its mantle. This means that, on earth, volcanoes are normally found where tectonic plates are either converging or diverging. It is worth noting that most of them are found underwater. For example, the Mid-Atlantic Ridge has volcanoes that are brought about by divergent tectonic plates. The Pacific Ring of Fire, on the other hand, has volcanoes that are brought about by convergent tectonic plates.
Volcanoes can also be formed in areas where there is stretching as well as thinning of the plates of the crust. This type of volcanism is said to fall under the umbrella of the so-called “plate hypothesis” volcanism. The plate hypothesis suggests that "anomalous" volcanism results from the lithospheric extension that permits melt to rise passively from the asthenosphere beneath.
Volcanism that takes place away from plate boundaries is explained as mantle plumes. These so-called "hot spots", for example, Hawaii are fed by a region deep within the Earth's mantle from which heat rises through the process of convection. This heat facilitates the melting of rock at the base of the lithosphere, where the brittle, upper portion of the mantle meets the Earth's crust. The melted rock, known as magma, often pushes through cracks in the crust to form volcanoes. Hot spot volcanism is unique because it does not occur at the boundaries of Earth’s tectonic plates, where all other volcanism occurs, Instead, it occurs at abnormally hot centers known as mantle plumes.
Mantle hotspots forming volcanoes
Erupting volcanoes can bring about many hazards, even further away from the point of eruption. An example of such hazards is that volcanic ash poses a threat to aircraft. Large eruptions may have an effect on temperatures as ash as well as sulfuric acid droplets obscure the sun and cool the lower atmosphere of the earth (the troposphere). These eruptions also absorb the heat that is radiated from the earth and therefore warms the upper atmosphere (the stratosphere).
These are flat linear fractures through which lava emerges.
These result from eruptions of mainly small pieces of pyroclastics and scoria that build up around the vent.
These are volcanoes that are formed by the eruption of lava of low viscosity capable of flowing a great distance from a vent. They normally do not explode catastrophically. Due to the fact that magma of low viscosity is low in silica, shield volcanoes occur more in oceanic than they occur in continental settings.
A stratovolcano which is also known as a composite volcano is a tall conical mountain that is composed of lava flows as well as other ejecta in alternate layers. Stratovolcanoes are also referred to as composite volcanoes since they are created from different structures during different types of eruptions. Strato or composite volcanoes are made of lava, ash, and cinders. Mount St. Helens, in Washington state, is a stratovolcano that erupted on May 18, 1980.
These are built by slow eruptions of lava that is highly viscous. They are at times formed in the crater of a previous volcanic eruption. Just like stratovolcanoes, lava domes can produce explosive and violent eruptions but their lava does not flow very far away from the vent of origin.
These are formed in cases where viscous lava is forced upward resulting in the bulging of the surface.
These types of volcanoes normally have a large caldera and are capable of producing devastation on a very large scale. These volcanoes are capable of severely cooling the global temperatures for many years following the eruption as a result of large volumes of sulfur and ash that is released into the atmosphere.
These are underwater vents or fissures in the Earth's surface from which magma can erupt. Manu submarine volcanoes are located near areas of tectonic plate formation, known as mid-ocean ridges. The volcanoes at mid-ocean ridges alone are estimated to account for 75% of the magma output on Earth. Although most submarine volcanoes are located in the depths of seas and oceans, some also exist in shallow water, and these can discharge material into the atmosphere during an eruption.
Kavachi in the Solomon Islands is an active, submarine volcano
A subglacial volcano, also known as a glaciovolcano, is a volcanic form produced by subglacial eruptions or eruptions beneath the surface of a glacier or ice sheet which is then melted into a lake by the rising lava. They are most common in Iceland and Antarctica. They are made up of flat lava which flows at the top of extensive pillow lavas and palagonite. When the icecap melts, the lava on top collapses, leaving a flat-topped mountain. These volcanoes are also called table mountains, tuyas, or uncommonly mobergs.
A mud volcano or mud dome is a landform created by the eruption of mud or slurries, water, and gases. Several geological processes may cause the formation of mud volcanoes. Mud volcanoes are not true igneous volcanoes as they do not produce lava and are not necessarily driven by magmatic activity. The Earth exudes a mud-like substance, which may sometimes be referred to as a "mud volcano". Mud volcanoes may range in size from merely 1 or 2 meters high and 1 or 2 meters wide to 700 meters high and 10 kilometers wide. Smaller mud exudations are sometimes referred to as mud-pots. Azerbaijan has the most mud volcanoes of any country.
The magma chamber is a hollow within the volcano where magma and gases accumulate. During an eruption, these volcanic materials move from the magma chamber toward the surface via a pipe-like passageway called a conduit. Some volcanoes have a single conduit, while others have a primary conduit with one or more additional conduits that branch off it.
A vent is an opening on the surface of a volcano that emits lava, gases, ash or other volcanic materials. Some volcanoes have multiple vents, but there is only one main vent, or central vent.
At the top of the volcano, the central vent may be surrounded by a bowl-shaped depression called a crater. Craters form when explosive eruptions occur. Eruptions are more explosive when magma contains a lot of gases and the volcano forcefully expels a large quantity of ash, rock fragments along with those gases.
The slopes are the sides or flanks of a volcano that radiate from the main or central vent. Slopes vary in gradient depending on the intensity of the volcano’s eruptions and the materials that are expelled. Explosive eruptions of gas, ash and solid rock create steep slopes. Slow-flowing molten lava creates gradual slopes.
Parts of a volcano
Magma is liquid rock inside a volcano. Lava is a liquid rock (magma) that flows out of a volcano. Fresh lava glows red hot to white-hot as it flows.
When rock beneath the earth’s surface gets really hot, it becomes molten or liquid. While it’s still below the surface, it’s called magma. Once the magma erupts to the surface through a volcano, it’s called lava. The hotter and thinner the lava is, the farther it will flow. Lava can be very hot, sometimes as hot as 1000°C.
Eventually, lava on the surface will stop flowing and cool and harden into rocks. Rocks formed from lava cooling are called igneous rocks. Some examples of igneous rocks include basalt and granite.
Scientists have categorized volcanoes into three main categories: active, dormant, and extinct.
