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INTRODUCTION
A volcano is a rupture in the earth’s crust through which hot lava (molten rock), gasses, volcanic ash, are emitted outwards from a magma chamber underground. Volcanoes have created over 80% of the earth’s surface. They are present on every continent, including Antarctica. Volcanic vents open up in those parts of the earth’s crust where the rock layers are comparatively weaker. Volcanic eruption is an example of an internal explosion. Depending on how explosive the volcanic eruption was, different landforms such as a plateau or mountain are formed. The study of volcanoes is known as volcanology. There are around 1500 active volcanoes in the world today.
Causes of volcanism
- In the interior of the earth, radioactive substances undergo chemical reactions generating explosive amounts of heat. Further, residual heat contained at the center of the earth while formation during its formation is also present. This creates a huge temperature difference between the inner and the outer layers of the earth.
- This extreme difference in temperature leads to the formation of convection currents in the Mantle which creates convergent and divergent plate boundaries. Due to this, the molten magma and gaseous materials come out to the earth’s surface at the first available opportunity.
- The subduction of a denser plate occurs at the convergent boundary and creates magma at high pressure which escapes to the surface in the form of volcanic eruptions.
- Sometimes, an earthquake could expose fault zones on the crust through which Magma may overflow to the surface leading to fissure type volcanoes.
Types of volcanoes
Shield Volcanoes
Amongst the largest of all the volcanoes on the earth, shield volcanoes are mostly made up of basalt. They are gently sloping and have very thin lava layers on all sides of the central vent. They are usually characterized by low explosivity but become explosive if water gets into their vent. The lava emanates from the cone in a fountain-form and then develops into a cinder cone.Examples are the Hawaiian shield volcanoes.
Composite volcano
The layers stack on one another with each eruption. The volcanoes form steep cones, instead of rounded shapes, because the magma is viscous. Composite volcano magma is felsic, which implies it contains silicate-rich minerals rhyolite, andesite, and dacite. Subduction occurs when two convergent tectonic plates touch one another. Water is trapped in porous basalt and minerals. because the plate sinks to greater depths, temperature and pressure rise until a process called “dewatering” occurs. The composite volcanoes tend to be chained with each volcano even several kilometers from the following. The “Ring of Fire” within the ocean consists of stratovolcanoes. Most composite volcanoes occur in an exceedingly large region called the Ring of fireside. To date, composite volcanoes have only been found on one other body within the solar system: Mars. Composite volcano magma isn’t fluid enough to flow around obstacles and exit as a river of lava. These molten chunks of rock is also the scale of small stones up to the scale of a bus. Composite volcanoes also produce lahars. Semeru Volcano in Indonesia is a lively stratovolcano. Death and property damage aren’t the sole consequences of composite volcanoes. Particulates released by these volcanoes cause colorful sunrises and sunsets. Gas released into the atmosphere can form sulphuric acid. The eruption of Mount Tambora in 1815 produced a cloud that lowered global temperatures 3.5 C (6.3 F), resulting in the 1816 “year without a summer” in North America and Europe. The world’s biggest extinction event may be due, a minimum of partly, to stratovolcanic eruptions. A gaggle of volcanoes named the Siberian Traps released massive amounts of greenhouse gasses and ash, starting 300,000 years before the end-Permian mass extinction and concluding half 1,000,000 years after the event.
CINDER CONE VOLCANO
They consist of a steep conical hill of concealed lava that has been ejected from a single vent. They are also known as pyroclastic cones and are the smallest and simplest types of volcanoes. As the loose pyroclastic material is blown into the air, it breaks into small fragments which solidify and fall as cinders around the main vent. They have highly fluid basaltic lava. Examples include Paricutin and the Dragon Cone.
They are constructed from numerous explosive eruptions and characterized by outbreaks of cooler and more viscous lavas than basalt. They have a conduit system of vents which leads up from the magma reservoir below. Their eruption also contains large quantities of pyroclastic material and ashes which gather near the vent openings and result in the creation of layers. Thus, they are built of alternate layers of blocks of unmelted stone, lava flow and ash. The Pacific Rim, also known as the “Rim of Fire” is a composite volcano chain, whereas the Mayon Volcano in the Philippines, Mount Fuji in Japan, and Mount Rainier in Washington are some other composite volcanoes in the world. They are also known as stratovolcanoes.
Calderas
Generally the most explosive volcanoes on Earth usually collapse on themselves and do not construct new structures. These collapsed structures are known as calderas. They are bowl-shaped depressions and are of three types. The first type is a crater lake, an example of which is the Crater Lake of Oregon. This forms when a stratovolcano collapses on its magma chamber. The second is the Basaltic Shield calderas which are gradually enlarged by episodic collapse, for example, the Kilauea caldera. The third type are the Resurgent Calderas which are the largest volcanic structures on Earth. They are formed due to massive eruptions of pyroclastic sheet flows and are characterized by broad topographic depressions for instance the Valles Caldera in New Mexico.
Flood Basalt Volcanoes
These volcanoes discharge lava that is extremely fluid and flows for long distances. Many parts of the world are covered by these, for instance the Columbia River Basalt Group.
Mid-Ocean Ridge Volcanoes
Mostly found in the oceanic areas, the central region of this ridge gets frequent eruptions. A system of mid-ocean ridges stretches for over 70000 km through ocean basins, e.g., Axial Seamount on the Juan de Fuca ridge.
Earthquakes
An earthquake is defined by the shaking of the Earth’s surface which results from a sudden release of energy in the Earth’s outer layer that generates waves that travel in all directions. These waves are known as seismic waves. They are recorded on seismographs. The place below the earth’s surface where the earthquake begins is known as the hypocentre, but the place on the earth’s surface is known as the epicenter. After the earthquake, the rock plates start moving again, until they get stuck again.
Seismic waves are elastic waves of energy that are caused by movements of earth’s tectonic plates or when an earthquake occurs.
There are two kinds of body waves inside the Earth. The p-waves and the s-waves.
The p waves, also known as primary waves, are the fastest seismic waves. They are longitudinal compressional waves and can move through solid, liquid or gas. The s-waves or the secondary waves on the other hand are slower than p-waves. Their motion is perpendicular to the plane in which waves travel. They can only travel through solids. The earthquake waves above the earth are known as surface waves.
Talking about the difference between p waves and s waves, the first wave which hits seismographs are p waves while the second waves which hites the seismographs are s waves. Also, p waves are compression waves and s waves are shear waves. In terms of direction, p waves shake the medium in the direction of which their propagating while s waves shake the medium at 90 degree to which they are moving.
Causes of earthquakes
Plate Movements: Upwarping and downwarping of the earth’s crust and folding and faulting of the rock strata are some of the main reasons that earthquakes occur. This means that it happens when two blocks of the earth, called tectonic plates, suddenly slide past each other. The surface where they slip is called the fault or fault plane. Examples of earthquakes caused due to plate movements are the Assam earthquakes of 1951 and the San Francisco earthquakes in 1906.
Volcanic eruptions
Explosive volcanic eruptions cause vibrations in the earth’s crust and put solid rocks under great stress. However, these earthquakes only occur in regions of volcanic activity such as the Pacific ring of fire and the Mid-Atlantic Ridge. The earthquake that came before the eruption of the Mauna Loa volcano of the Hawaii Island in 1868 is an example of a volcanic earthquake.
Forces within the earth
The gasses within the earth’s surface sometimes expand and contract causing stress in the earth’s strata that builds up over time and is sometimes suddenly released out in the form of earthquakes.
Exogenic forces
A landslide or the collapse of a cave may cause a certain release of energy which sometimes also leads to an earthquake.
Man-made causes
Man-made causes such as mining, building of dams and roads, drilling etc. Also causes earthquakes.
Distribution of earthquakes
Most earthquake zones are often found in clusters in or close to tectonic plate boundaries. There are three large zones on the earth where earthquake clusters are found.
- Circum-Pacific seismic belt: Also known as the Pacific Ring of Fire, it is the world’s largest earthquake belt. It is a horse-shoe-shaped belt. More than 70% of all earthquakes are present here. Located in the Pacific Ocean, it stretches across 15 countries and is characterized by active volcanoes and is a great producer of geothermal energy.
- Alpide earthquake belt: This belt extends from Java to Sumatra, passing through the Mediterranean region and moving east from Asia and where it connects with the Circum-Pacific Belt. It contains about 17 percent of the world’s largest earthquakes and includes the Atlas Mountains, the Alps and the Caucasus Mountains.
- Submerged mid-Atlantic Ridge: One of the largest geological features on the planet, the mid-Atlantic Ridge marks a divergent plate boundary or the place where two tectonic plates are spreading apart. This ridge is mostly underwater and lies along the north-south axis of the Atlantic Ocean.
Conclusion
Volcanoes have created over 80% of the earth’s surface. They are present on every continent, including Antarctica. In the interior of the earth, radioactive substances undergo chemical reactions generating explosive amounts of heat. This creates a huge temperature difference between the inner and the outer layers of the earth. This extreme difference in temperature leads to the formation of convection currents in the Mantle which creates convergent and divergent plate boundaries. Amongst the largest of all the volcanoes on the earth, shield volcanoes are mostly made up of basalt. They consist of a steep conical hill of concealed lava that has been ejected from a single vent. They are also known as pyroclastic cones and are the smallest and simplest types of volcanoes. They have a conduit system of vents which leads up from the magma reservoir below. They are also known as stratovolcanoes. Generally the most explosive volcanoes on Earth usually collapse on themselves and do not construct new structures. They are bowl-shaped depressions and are of three types. These volcanoes discharge lava that is extremely fluid and flows for long distances. Many parts of the world are covered by these, for instance the Columbia River Basalt Group. Mostly found in the oceanic areas, the central region of this ridge gets frequent eruptions. An earthquake is defined by the shaking of the Earth’s surface which results from a sudden release of energy in the Earth’s outer layer that generates waves that travel in all directions. They are recorded on seismographs. Seismic waves are elastic waves of energy that are caused by movements of earth’s tectonic plates or when an earthquake occurs. There are two kinds of body waves inside the Earth. The p-waves and the s-waves. They are longitudinal compressional waves and can move through solid, liquid or gas. The s-waves or the secondary waves on the other hand are slower than p-waves. Plate Movements: Upwarping and downwarping of the earth’s crust and folding and faulting of the rock strata are some of the main reasons that earthquakes occur. Explosive volcanic eruptions cause vibrations in the earth’s crust and put solid rocks under great stress. The earthquake that came before the eruption of the Mauna Loa volcano of the Hawaii Island in 1868 is an example of a volcanic earthquake. Man-made causes such as mining, building of dams and roads, drilling etc. Most earthquake zones are often found in clusters in or close to tectonic plate boundaries. There are three large zones on the earth where earthquake clusters are found. Circum-Pacific seismic belt: Also known as the Pacific Ring of Fire, it is the world’s largest earthquake belt. Alpide earthquake belt: This belt extends from Java to Sumatra, passing through the Mediterranean region and moving east from Asia and where it connects with the Circum-Pacific Belt. It contains about 17 percent of the world’s largest earthquakes and includes the Atlas Mountains, the Alps and the Caucasus Mountains. Submerged mid-Atlantic Ridge: One of the largest geological features on the planet, the mid-Atlantic Ridge marks a divergent plate boundary.
