Throughout the eruption types of volcanoes in the world, the first determining factor is the composition, volatile content, temperature and viscosity of magma, such as basalt magma containing SiO two The composition is low, the volatile content is relatively low, the temperature is high, and the viscosity is low, so the magma has a large mobility, the volcanic eruption is relatively quiet, and most of it is the eruption of magma, which can form a large area of lava platform and shield volcano; Rhyolitic and andesitic magma is rich in SiO two And volatile matter, which have low temperature, high viscosity and poor liquidity, so the volcano erupts violently with huge explosion sound, a large amount of volcanic ash and volcanic bombs erupt, often forming tall pyroclastic cones, accompanied by pyroclastic flows and luminous clouds, often causing serious disasters. The second decisive factor is the characteristics of the underground magma ascending channel. If the magma in the magma chamber flows out of the surface along a long fault line, it will form fissure eruption; If the cylindrical channel formed along the intersection of two groups of faults is upwelling, under the action of internal pressure of magma, violent central eruption can be generated. The third decisive factor is the tectonic environment of magma eruption, depending on whether it is on land or underwater; Is it in the ridge or in the plate; Is it in the island arc or in the collision zone, etc.
1. Basalt overflow eruption
Such eruptions are like the Deccan Plateau in India and the Columbia Plateau in North America. They are magma rising along a major fault (fissure) or fault group in one direction and ejecting out of the surface, and some of them eject from a narrow and long channel; Some volcanoes erupt in a straight line, but they are connected downward to form a wall like channel, so they are called "fissure eruption". The eruption is dominated by basalt, the flow direction is nearly parallel, the thickness and composition are relatively stable, and the occurrence is gentle. Lava is commonly seen, often forming a lava plateau. Basalt is also called because of its high fluidity, large lava eruption and few explosive phases. It seems to flood everywhere in flat terrain with a wide distribution area“ Flood basalt ”。 In 1783, Laki Volcano in Iceland erupted, about 12km from a 25km long fissure three Lava and 3km three Of volcanic debris, covering an area of 565km two 。 The Willem Valley in Arizona, USA, flows lava from a 120m wide fissure at one time, forming 14 × 22km two And the maximum thickness is 240m. Permian basalt in Guizhou, Yunnan and Sichuan, China (260000 km two ）And Hannuo Dam in Hebei Province (1700km two ）It is also basalt flood eruption. two Hawaii Hawaiian eruption It is a hotspot volcano, represented by Hawaii Island in the United States. It is characterized by few explosions, and a considerable amount of basaltic lava flows often overflow from the mountaintop crater and the mountainside fissure. The magma has low viscosity and high liquidity, which is characterized by relatively quiet overflow, and the amount of gas released can be more or less. As the magma is subject to greater static pressure and bubble expansion during eruption, when it reaches the surface, it forms a lava fountain. The lava fountain driven by the escaping gas can be as high as 300m or more. Most of the ejected lava is basaltic lava, or andesitic lava, but also a small amount of volcanic slag and ash. In this type of eruption, the lava often overflows for many times, and there are many fissures as channels. The lava flowing out forms a relatively flat lava dome. For example, the eruptions of Kilauea in 1924 and Mauna Loa in 1975 are typical Hawaiian eruption 。 This type of eruption basically has no casualties, but it can destroy farmland and villages and cause property losses. 3. Strombolian eruption
From Italian in the early 20th century. The most typical is Italy's Stonebury Volcano, located on the Sicilian Aeolus Island, which often has volcanic eruptions. It has been known as the "lighthouse of the Mediterranean" since ancient times. Its eruptions are characterized by more or less regular moderate intensity eruptions, which eject hot lava. Its viscosity is larger than that of the Chevy type, accompanied by white vapor clouds. The lava at the crater is slightly hardened, mainly massive lava, composed of basaltic and andesitic rocks. The lava flow is thick and short, and a few are rope shaped. Gas escapes from it every half an hour. This kind of volcano rhythmically ejects white hot volcanic slag, volcanic gravel and volcanic bombs. The explosion is relatively mild. Many volcanic debris fall back into the crater and are ejected again. Others fall onto the slope formed by the volcanic cone and roll into the sea. For example, Stonebury Volcano (Italy), Palikutin Volcano (Mexico), Vesuvius Volcano (Italy), Avachin Volcano, and Kryuchev Volcano (the former Soviet Union) all have the characteristics of Stonebury type eruption.
four Vulcanian eruption (Vulcanian eruption) Vulcano Island is located near Sicily in the Mediterranean Sea. This type of eruption is more viscous than Stonebury type volcanic lava, in the form of molten slurry, and the eruption is more violent. When no eruption occurs, a thick consolidated crust is formed on the crater, and gas accumulates under the consolidated crust, making the upper gas of the lava column tend to be saturated. When the pressure increases, a violent explosion will occur, sometimes enough to destroy a part of the volcanic cone, so that the blockage will be blown open, and some fragments and lava "crusty volcanic bombs" and volcanic slag will be ejected together, accompanied by a "cauliflower like" eruption cloud containing a considerable amount of volcanic ash. When the "blockages" of the crater are ejected, lava flows out from the cracks on the side of the crater or cone.
five Pellet eruption (Peléan eruption) The name originates from the eruption of Mount Perry on Martinique Island in the West Indies in 1902, which destroyed the city of Saint Pierre with more than 30000 deaths. This eruption produces high viscosity magma, and the eruption is particularly strong. The most obvious feature is the generation of hot volcanic ash cloud, which is a high heat gas, full of hot volcanic ash particles, like active emulsion, with high density. When it moves down the slope, it is enough to produce hurricane like effects. In the Bailey type eruption, the upward escaping gas is often blocked by the lava in the crater. When the pressure gradually increases, the explosion is like a gust of wind blowing horizontally from the bottom of a bottle stopper. Lava is pushed out by gases with high ash content, but there is no lava flowing out of other places except from the crater. In history, there were many Perry type eruptions: in 1835, Corsica, 1883, Karakato, 1902, Sufriel, 1912, Katmai, 1951, Lamington Volcano, 1955-1956, Bezmiyan, 1968, Ma Rong and 1982, Elchijon Volcano eruptions all belonged to this type.
six plinian eruption (Plinian eruption) Magma is characterized by high viscosity and strong eruption. Volcanic debris is often more than 90%, of which wall rock debris accounts for 10% - 25%. The ejecta are mainly rhyolitic and trachytic pumice and volcanic ash, which are widely distributed, accompanied by a small amount of lava flow or ash flow. Due to the strong eruption and massive ejection of magmatic materials, a caldera with collapsed cone top is often formed. This kind of volcanic eruption process is often as follows: clearing the volcanic channel - magma foaming - violent eruption of pumice and volcanic ash - crushed stones on the channel wall falling into and blocking the volcanic channel, and so on, forming complex volcanic institutions. The eruption of Vesuvius in AD 79 was a typical Pliny eruption, accompanied by a large-scale fall of pumice, volcanic slag and ash. The ejected volcanic slag falls down with the wind, and Pompeii City, 13 km away from the crater, is buried by an average 7 m thick pumice layer. The shallow volcanic activity in Japan in 1783 also lowered the pumice layer Pyroclastic flow And the eruption of lava flows. May 18, 1980 Mount St. Helens The eruption is also Pliny type, forming hydrothermal magma explosion. 7. Super Vulcano eruption
Like water vapor eruption, it is almost an explosive eruption without magmatic material. Some are called supervolcanoes (Iwatiyama, Japan) type eruptions. Since the eruption only has eruptive material and no lava, the eruptive material is emitted in a cooling state, and occasionally in a hot state. It is characterized by a large amount of basement volcanic debris, sometimes up to 75% - 100%. The volume of the material emitted by the super Vulcano type eruption varies greatly, from giant rock blocks to volcanic ash. The clasts are usually angular and sharp, without volcanic bombs and slag.
8. Souterset eruption
From 1963 to 1967, a continuous volcanic eruption off the coast of southern Iceland produced a Soutese volcanic island. In the first half of the volcanic activity, a crater on the shallow sea floor was characterized by repeated explosive eruptions. When the basaltic magma came into contact with the sea water, it exploded again, producing a large amount of fine-grained materials (volcanic ash). This type of magma steam, steam magma eruption is different from the onshore Stonebury type eruption.
The above classification method is not the most perfect. The actual survey reveals that even the same eruption type may have different types of volcanism, and the same volcano may have different eruption types in its own activity process, and even in the same eruption period, there are different forms of volcanic activity sometimes. For example, the Stonebury volcano, named after the Stonebury type, has experienced several Vulcano type eruptions; It is named Hawaiian style. [1]
