Volcanism – Indonesia is one of the countries with the most volcanoes in the world. Of the 127 active volcanoes, only 69 have been monitored with tools, especially seismic equipment which is a minimum standard and is supervised by PVMBG. The pacific ring of fire where many volcanoes are located, the mountains of Indonesia are in the region.
Geologically, Indonesia is located between four tectonic plate collisions, which makes it overgrown with volcanoes. Volcanoes can erupt and release magma, volcanic ash and tephra. Apart from having an impact on volcanic eruptions, volcanic activity also fertilizes the soil, so that it can be used as forest areas, plantations, and tourism areas. Indonesia has three types of volcanoes, type A, B and C volcanoes.
In addition to volcanoes on land, Indonesia also has underwater volcanoes. These underwater volcanoes are invisible to the naked eye on the surface and hidden deep beneath the sea or ocean, and can cause natural disasters. Undersea volcano research is still very rarely done.
In history, several volcanoes in Indonesia erupted violently and caused many fatalities and even changed the lives around them. The volcano is known to be active and often erupts. In Indonesia, there are active volcanoes with an average of 100 years, 50 years and under 10 years. Mount Galunggung is an example of a volcanic eruption with an average rhythm of about once every 100 years. A volcano that erupts once every 50 years is an example of Mount Agung. While under 10 years, for example Mount Merapi, Mother, Dukono.
One of the most active volcanoes in Indonesia is Merapi. The eruption cycle of Mount Merapi is fairly routine, occurring every 2 and 5 years. Recorded since 1548, Mount Merapi has erupted 68 times. The 2010 eruption was an explosive eruption accompanied by explosions and rumbling sounds that could be heard up to 20-30 km away.
Within a period of 800 years, Indonesia produced three giant calderas, namely the Rinjani Volcano Caldera in 1257, the Tambora Volcano in 1815, and the Krakatau Volcano in 1883. In addition, the famous volcanic eruptions are Kelud, Galunggung, Toba , and Papandayan.
Among others, the explosive eruption of Toba about 73 thousand years ago was larger than Tambora in 1815, and had a Volcano Exploitation Index of 8. The magnitude of this super-eruption and the widespread distribution of the Youngest Toba Tuff (YTT) in the sea core of the Indian Ocean, the The Arabian and South China Seas have sparked ongoing debates about their global and regional impacts on prehistoric climates, ecosystems and human populations.
The following is a complete review of volcanism, see the information!
Definition of Volcanism
Volcanism is all events associated with the release of magma to the earth’s surface. Volcanic events are related to the formation of volcanoes, namely the movement of magma from within the lithosphere that infiltrates the upper layers or reaches the earth’s surface. Inside the lithosphere, magma occupies a pocket called a magma chamber (Batholit).
The depth and size of the magma chamber varies greatly. There are magma chambers that are located very deep and some are close to the surface of the earth. This difference in location is the cause of the difference in the strength of the eruption that occurred. In general, deep magma chambers cause more violent eruptions than shallow ones.
Magma can be interpreted as incandescent silicate material consisting of solid rock), liquid, and gas that is in the earth’s crust (lithosphere). Various kinds of gases contained in magma include water vapor, sulfur oxides (SO2), Hydrocarbon Gases or Hydrochloric Acid (HCL), Hydrosulfuric Gases or Sulfuric Acid (H2SO4). Magma activity is caused by the high temperature of the magma and the amount of gas it contains.
There are two forms of magma movement associated with volcanism, namely magma intrusion and extrusion.
1. Magma Intrusion
Magma intrusion is the breakthrough of magma into the layers of the lithosphere, but does not reach the earth’s surface. Magma intrusion can be divided into five, including:
- Batholit, namely magma chamber.
- Flat intrusion (sill or intrusion plate), namely magma that infiltrates between two layers of rock, horizontally and parallel to the layers of rock.
- Lakolit, namely magma that breaks through between the top layers of the earth. It looks like a convex lens or a muffin.
- Alleys (coroks), which are rocks resulting from magma intrusion that infiltrates and freezes between the folds (coroks).
- Diatrema is a hole (pipe) between the magma chamber and the volcanic crater which looks like an elongated cylinder.
Formation resulting from magma intrusion is a very important mineral resource economically. Because in the intrusion area, various minerals such as diamonds, copper, iron, gold, silver and
other metallic and non-metallic minerals are often found.
2. Magma Extrusion
Magma extrusion, namely the process of releasing magma from inside the earth to above to the earth’s surface. The extruded magma material can be:
- Lava, namely magma that comes out to the surface of the earth and flows to the surface of the earth.
- Lahar, which is a mixture of lava and materials on the surface of the earth in the form of sand, gravel, dust, etc., and water, forming mud.
- Eflata and pyroclastics, namely solid materials in the form of bombs, lapilli, gravel, and volcanic ash.
- Echalation (gas) is material in the form of carbonic acid gas such as fumarole (a source of water vapor and limp substances), solfatar (a source of sulfur gas), and mofet (a source of carbonic acid gas).
Extrusion is synonymous with volcanic eruptions or eruptions which can be divided into two, namely effusive eruptions and explosive eruptions.
- Effusive eruptions, namely eruptions in the form of molten lava through cracks or fissures or crater holes of a volcano.
- Explosive eruptions, namely eruptions in the form of explosions by releasing solid materials (Eflata / Pyroclastics) in the form of bombs, lapilli, gravel, and volcanic ash together with gas and fluids.
According to the place where magma comes out, eruptions can be divided into three, namely:
- Linear eruption, namely the event of magma ejection through gaps or cracks that extend, thus forming a series of volcanoes.
- Areal eruptions, namely eruptions that occur when magma is close to the earth’s surface, then the magma burns and melts the rock layer above it, thus forming a large hole on the earth’s surface.
- Central eruption, if the eruption occurs out through a hole that forms separate volcanoes.
Central eruptions produce three forms of volcanoes, which are as follows:
- Shield volcanoes ( Shield Volcanoes ), which are volcanoes with wide bases and gentle slopes, are the result of effusive eruptions of molten magma. For example, the volcanoes that spread across the Hawaiian Islands.
- Maar volcano, is the result of an explosive eruption that is not too strong and only once. For example, Mount Lamongan, East Java, with its Klakah crater.
- Strato volcanoes, or cones, are the result of repeated, effusive and explosive mixtures. This volcano is conical in shape and its body is layered. As a result of eruptions that move from center to place, cones of volcanoes form here and there, so that the shape of the volcano is irregular. Most of the volcanoes in Sumatra, Java, Bali, Nusa Tenggara and Maluku are cone volcanoes. Examples of Strato Volcanoes are Mount Kerinci, Merapi, Ciremai, Semeru, Batur, Tangkuban Perahu, and Mount Fujiyama in Japan.
Eruption Type
After understanding the meaning of volcanism, there are also types of area. Based on the viscosity of the magma, gas pressure, depth of the magma chamber, and the material it ejects, volcanic eruptions are divided into several types, namely:
1. Hawaiian Type Eruption
The Hawaiian type occurs because the lava that comes out of the crater is very liquid, so it easily flows in all directions. This very fluid nature of lava results in a shape like a shield or shield. Examples: Mount Maona Loa, Maona Kea, and Kilauea in Hawaii.
2. Stromboli Type Eruption
This type of eruption is specific, that is, the eruptions occur at almost the same intervals or intervals. The Stromboli volcano in the Lipari Islands has an eruption period of ± 12 minutes. So, every ±12 minutes there is an eruption that spews material, bombs, lapilli, and ash. Examples of volcanoes with the Stromboli type are Mount Vesuvius (Italy) and Mount Raung (Java).
3. Volcano Type Eruption
This type of eruption ejects solid material, such as bombs, ash, lapilli, as well as solid and liquid materials or lava. This type of eruption is based on the strength of the eruption and the depth of the magma chamber. Example: Mount Vesuvius and Etna in Italy, and Mount Semeru in East Java.
4. Merapi Type Eruption
This type of eruption releases viscous lava that clogs the mouth of the crater. As a result, the gas pressure becomes increasingly strong and breaks the lava plug. The broken blockage was pushed up and finally thrown out. This material flows down the mountainside as ladu or gloedlawine . In addition, hot clouds ( gloedwolk ) or often called wedhus gembel occur . Merapi-type eruptions are very dangerous for residents in the vicinity.
5. Perret or Plinian type eruptions
This type of eruption is very dangerous and very damaging to the environment. The material ejected in this type of eruption reaches a height of about 80 km. This type of eruption can throw a rock or break into the top of the mountain, causing the crater walls to sag. Example: Mount Krakatoa which erupted in 1883 and St. Helens which erupted on May 18, 1980.
6. Pelee Type Eruption
This type of eruption usually occurs when there is a blockage of the crater at the top of the volcano which is shaped like a needle, causing the gas pressure to increase. If the crater blockage is not strong, the volcano erupts.
7. Sint Vincent Type Eruption
This type of eruption causes the crater lake water to spill over with the lava. This eruption caused the area around the mountain to be hit by hot lava which was very dangerous. Example: Mount Kelud which erupted in 1919 and Mount Sint Vincent which erupted in 1902.
Other Phenomena After Volcanism
Apart from volcanoes resulting from magma extrusion activity, there are several other natural phenomena that are formed from advanced or post-volcanism processes. These features include calderas, caldera lakes, lava plateaus, geysers, and mud pools.
1. Lava Plugs
The first post-volcanism phenomenon was the Lava Plug. This feature occurs when the solidified lava in a volcanic pipe collapses into a resistant mass.
Over time, the part of the volcanic cone composed of less resistant material weathered and eroded away, leaving only a plug of lava. The size of this lava plug can be very large to resemble a hill. One example is the Devil’s Tower in Wyoming, USA.
2. Caldera and Caldera Lake
A caldera is a large depression at the top of a mountain. This appearance occurred due to a very powerful eruption and left a large hole. If this hole is then filled with water it will form a caldera lake.
3. Plato Lava
This appearance occurs because the magma that comes out is runny, so it can spread and form a wide expanse of lava and over time this lava slowly freezes to form a plateau called a plateau.
4. Geysers and Hot Springs
In volcanic areas, groundwater can be heated by magma. This heated water can appear to the surface with explosive force, this is what is called a geyser. If this water comes out through the flow of water in the rock crevices, hot springs are formed. Geysers are hot water that emits periodically.
Positive and Negative Impacts of Volcanoes
The existence of volcanoes in an area, in addition to causing negative impacts in the form of disasters, such as eruptions, toxic gases and landslides which always threaten the surrounding population, in fact can also bring positive impacts in the form of enormous benefits for life, including the following:
1. Positive Impact
Volcanoes form a giant cone which affects the weather conditions and the surrounding climate, thus making the soil very fertile due to the rocks and minerals that make up the soil composition which is needed by plants. In addition, water is the source of life for all living things on the surface of the earth. When water seeps and flows into the ground in contact with a heat source from magma, a hot spring will form, while in the lower part of the ground it is an ordinary spring.
With lots of springs around the volcano and thick forests and other vegetation, it will form a cool and beneficial environment for the people who live around it. Forming plantations and rice fields, will add to the beautiful scenery and fresh air around it.
The existence of a volcano will produce natural forests, thus producing abundant forest products, and with all its contents in the form of living things as a resource for flora and fauna, as well as minerals that form the volcano.
The positive impacts of volcanoes can be broken down as follows:
- As an energy source, because the heat source from volcanoes can be used as Geothermal Power Plants (PLTPB) such as those on Mount Kamojang in West Java and Mount Dieng in Central Java.
- As a source of minerals and minerals, such as diamonds, tin, copper, sulfur and pumice.
- As a tourist and sports object, for example hiking, climbing, hang gliding, and mountain biking.
- As a fertile agricultural area, this is because the material released by the volcano contains many elements and minerals that can make the surrounding soil fertile and experience rejuvenation.
- As an orographic rain area, namely rain that occurs because of a barrier in the form of a mountain or mountains, so that the volcanic area is a place that has a hydrological function for the surrounding area.
- As a source of germplasm, because the vertical variation in the height of a volcano can cause living germplasm to vary greatly as well.
2. Negative Impact
In addition to having a positive effect, volcanic eruptions can also have a negative impact on life and the environment. Thousands of people died and several livestock died and thousands of hectares of gardens and rice fields were destroyed by volcanic eruptions. Disasters and the danger of volcanic eruptions affect directly and indirectly and can damage life.
The direct hazard is the hazard caused by the material released directly by the volcano. The disaster-prone areas that will be hit by this direct influence include the area around the peak (inside the crater) and develop into other areas around the crater, with a range that can reach more than 10 km.
If a crater filled with water forms a crater lake and the water is neutral with an acidity of 7 or is acidic with an acidity of less than 7 and mixed with river water, river water cannot be used for irrigation purposes, livestock drinks, especially for humans to drink. because it can damage the teeth of the residents.
This is due to the consumption of water containing very high fluorine (F) and a lack of iodine will result in goiter, while the ejection of volcanic ash during an eruption also threatens flight safety because the eruption ash disturbs the vision of the aircraft. The spread of this volcanic eruption will be very wide from a few meters to hundreds of kilometers.
Well, that’s an explanation of volcanism. The following is a recommendation of books from sinaumedia that Sinaumed’s can read to learn about volcanism so they can fully understand it. Happy reading.
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