Volcanoes and Earthquakes: Formation and Types
Volcanoes
A volcano is a geological structure from which magma (molten rock) and gases from inside a planet rise and emerge. This generally occurs in violent episodes called eruptions. A volcano is the only conduit that puts the terrestrial surface in direct communication with deep levels of the Earth’s crust. In the mantle’s depth, magma under pressure rises, creating magma chambers below or within the cracks in the rocks of the crust. The Earth’s crust provides an outlet for the intense pressure, and thus volcanic eruptions take place. Eruptions do not obey any law of frequency, and it has not been possible to discover a method to anticipate them. However, they are sometimes preceded by seismic shocks and the emission of fumaroles. Their violence is related to the acidity of the lavas and the gas content. A silica-rich lava, and therefore, acid, is characterized by a high viscosity that opposes the release of gases. They reach such high pressure and, when they overcome the resistance they encounter, escape violently, leading to an explosive eruption. By contrast, a basic lava is much more fluid and opposes little resistance to the detachment of its gases: the eruptions are less violent and can take a permanent character.
Types of Volcanoes
Hawaiian
Its lavas are very fluid, without giving rise to gaseous explosive outbursts, such as lava overflowing the crater and easily sliding down the slope of the volcano, forming veritable streams over long distances. For this reason, the Hawaiian-type volcanoes are gently sloping. Some particles of lava, being blown, form crystalline wire that natives called “hair of the goddess Pele” (goddess of fire). They are fairly common throughout the planet.
Strombolian
This type of volcano is named after Stromboli, a volcano on Lipari Island (Tyrrhenian Sea), north of Sicily. It is caused when there is an alternation of erupted materials, forming a cone of stratified fluid lava layers and solid materials. The lava is fluid, giving off rich and violent gases, with projections of slag, bombs, and lapilli. Because gases can easily fall off, there are no sprays or ashes.
Vulcanian
From the name of the volcano Vulcano in the Lipari Islands. It sheds large quantities of gas from a little fluid magma, which consolidates rapidly, so the explosions are very strong and pulverize the lava, producing lots of ash thrown into the air accompanied by other fragmentary materials. When lava is extruded, it solidifies rapidly, but the gases given off break and crack its surface, which is rough and therefore very irregular.
Earthquakes
An earthquake, also called a seism or simply a quake (in some areas, it is considered that a tremor or an earthquake is a quake of lesser magnitude), is a ground shaking produced by the collision of tectonic plates and the release of energy in the course of a sudden reorganization of the crust material to overcome the state of mechanical equilibrium. The most important and frequent ones occur when the stored elastic potential energy released in the gradual deformation of rocks adjacent to an active fault plane is released, but they can also occur from other causes, for example, about volcanic processes, by the collapse of karst cavities or slope movements. Tectonic earthquakes often occur in areas where the concentration of forces generated by the boundaries of tectonic plates results in readjustment movements inside and on the surface of the Earth. This is why earthquakes or quakes of tectonic origin are closely associated with the formation of geological faults. They usually occur at the end of a cycle called the seismic cycle, which is the period during which strain accumulates inside the Earth and is later released suddenly. This release corresponds to the earthquake, after which the strain begins to accumulate again.
The point inside the Earth where the earthquake occurs is called the seismic focus or hypocenter, and the point of the surface that is directly on the vertical of the hypocenter, and that, therefore, is the first affected by the shake, is called the epicenter. In an earthquake, one can distinguish:
- Hypocenter: The deep hinterland, which produces the earthquake.
- Epicenter: The surface area perpendicular to the hypocenter, where seismic waves affect more intensely.