Felsic has a lot of silica

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Explanation of volcanological terms and technical terms:

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accretionary lapilli

Accretionary lapilli in a layer of the Santorini volcano in Greece
Round balls of volcanic ash
Accretionary lapilli are small spheres that are created by electrostatic charge / moisture in volcanic explosion clouds. They remind a little of the clay pebbles in hydroponics ... Full entry


Typical sample of andesite from a volcanic dome from the Methana peninsula in Greece
Andesite is a gray to black volcanic rock with a proportion of 52-63% silicon (SiO²). Andesite forms most of the lava domes and stratovolcanoes.
Andesite is a fine-grained rock that belongs to the class of igneous, volcanic rocks. It usually has a gray, brown-purple to black color.
Andesite is a volcanic rock ("effusion rock") that occurs particularly in subduction zones. It consists of around 60 percent by weight of silica and emerges as very tough lava at temperatures of around 950 to 1,000 degrees Celsius ... Entire entry


Volcanology: volcanic ash
Ash cloud from an explosion of the Etna volcano
Fine-grained, volcanic rock (approx. 0.5-2 mm), which is formed in explosive volcanic eruptions and can be transported far.
Volcanic ash has nothing to do with ash from organic combustion processes. Ash is defined by a grain size of approx. 0.5 mm - 2 mm. This ash is fine-grained lava, which, due to its size and weight, can easily be carried by the wind. The ash can consist of pieces of amorphous lava, crystal fragments, and glass. The volcanic ash is produced by strong, volcanic explo ... Entire entry

Related entries (10):

Etna - ash fall - base surge - explosive - Milos - Nisyros - Santorini - cinder cones - Vulcano - volkane / lexicon.html


Volcanology: volcanic ash rain
Ash cloud and ash fall during an eruption of Mount Etna in 2002
Volcanic ash is the deposit of very fine-grained volcanic products
Volcanic ash fall is the deposition of very fine-grained volcanic products in the form of "rain", which can occur dry or, if the eruption column is at a higher height, mixed with water (wet). Volcanic ash can be transported over many kilometers and even get into the stratosphere and be distributed all over the world. Entire entry

Related entries (3):

Etna - Ash - Base surge


Basalt is the most common volcanic rock in the world. It is poor in silicon and very fluid as a melt (magma, lava in the event of an eruption). Volcanic eruptions, during which basaltic magma emerges, therefore mainly produce lava flows.
Basalt is a basic (low-silica) volcanic rock. It mainly consists of a mixture of iron and magnesium silicates with olivine and pyroxene as well as calcium-rich feldspar (plagioclase). Basalt is usually dark gray to black. For the most part, it consists of a fine-grained matrix. Coarser insects that can be seen with the naked eye are relatively rare, but can ... Entire entry

Base surge

Base-surge deposits on Santorini (ca.1613 BC)
Ember-shaped, gas and dust avalanches that can occur during volcanic eruptions.
Base surges are hot avalanches of gas (steam, sulfur, etc.), dust and ash that travel at several hundred km / h.

They arise from volcanic, phreatomagmatic volcanic eruptions. Enormous amounts of overburden and magma or lava are shot at heights of several kilometers.

If this eruption column (Plinian column) collapses, fallouts arise (... Entire entry

Related entries (5):

Ash - ash fall - pumice - Santorini - volcanoes / lexicon.html


Our tour guide Marta poses in Lipari pumice stone ...
Pumice stone (pumice) is a very light, very porous and mostly light-colored volcanic rock that is formed when very gaseous and viscous lava foams and solidifies as foam.
Pumice is formed in explosive eruptions of mostly very silicon-rich ("acid") magma. The proportion of gas bubbles is usually so high that the pumice stone is lighter than water and floats.
As a basic material for high-quality cements and insulating lightweight building blocks, pumice is a sought-after industrial raw material.
Pumice stone is a textural term for a volcanic rock, which is a compacted foamy lava of very microvesicular glass pyroclastic with very thin, translucent bubble walls of extrusive igneous rock. It is usually, but not exclusively, from silicate or volcanic to intermediate in composition (e.g. rhyolite, dacitic andesite, pantellerite, phonolite trachyte), ... full entry


Volcanology: (volcanic) block
Large block of lava that came out of a crater during the Minoan eruption (1627 BC) on Santorini
Lava blocks are solidified fragments larger than 64 mm that are ejected from craters during explosive volcanic eruptions. They can consist of older, cooled lavas that were torn off from e.g. the crater.
During massive volcanic eruptions, large pieces of rock can be blasted out of a crater / conveyor / magma chamber, which - depending on the strength of the eruption - can weigh several tons and can be shot out of the crater up to kilometers. They reach speeds of approx. 200-300 m / sec. And can cause great damage when they hit (e.g. in buildings!). Through the ... Entire entry

Related entries (2):

Block lava - bread crust bomb

Block lava

Volcanic center of the volcanic dome on Methana
Lava flow consisting of large blocks of solidified lava on the surface.
Especially in the case of tough, andesitic / dazitic lava, the lava is not flowable. Dan pushes the fresh material along large, solidified lava holes. This block lava occurs particularly in lava domes, e.g. during the historical volcanic eruption on the Methana peninsula in Greece. Entire entry

Related entries (2):

Block - bomb


Volcanology: volcanic bomb
Large bomb that was ejected from one of the craters on Etna
Ejected fragments of fresh lava that are larger than 64 mm and that have often acquired an aerodynamic shape in their flight.
Ejected fragments of fresh lava that are larger than 64 mm and that have often acquired an aerodynamic shape in their flight. There are different types of volcanic bombs, depending on the shape they took on when they cooled: "bread crust bombs", "pita bombs", "spindle bombs", etc. Complete entry

Bread crust bomb

Bread crust bomb, approx. 50 cm long, from Lokon volcano (N-Sulawesi, Indonesia)
Volcanic bomb that cracked when it cooled, resembling farmhouse bread.
Breadcrust bombs are created when a volcanic bomb slowly cools down. The temperature differences inside the bomb to the outer edge area create strong tensions which lead to the shell tearing. Such bombs resemble a loaf of farmer's bread. Entire entry

Related entries (3):

Pumice block cinder cone


A dacitic lava-dome at Nisyros Island in Greece
Dacite is a volcanic rock with a relatively high content of silicon located between andesite and rhyolite.
Dacite (pronounced / deɪsaɪt /) is an igneous, volcanic rock with a high iron content. It is intermediate in compositions between andesite and rhyolite, and, like andesite, it consists mostly of plagioclase feldspar with biotite, hornblende, and pyroxene (augite and / or enstatite). It has an aphanitic to porphyritic texture with quartz as rounded, corroded phenocrysts, or as an element of t ... Entire entry


Volcanology: effusive (volcano) eruption
Lava flows are the typical form of eruption of effusive eruptions (here an example from Etna)
Effusive means outflow, outflow of magma (-> lava flows)
When magma arrives at the surface and is sufficiently liquid and escaping gases do not tear the magma apart and throw it high into the air, this type of eruption is called effusive. The result is lava flows. This type of volcanism is also referred to as "red volcanism", or the volcanoes that mainly have effusive eruptions as "red volcanoes". Entire entry

Related entries (2):

Etna - explosive


Volcanology: explosive (volcano) eruption
A small explosive eruption on Etna
If magma is thrown into the air as fragments (ash, lapilli, bombs) when it emerges, it is called an explosive eruption (as opposed to effusive).
Explosive volcanic eruptions mean that the magma is fragmented as it emerges. The cause is spreading gases, which when the pressure drops on the surface, similar to carbon dioxide in the opened champagne bottle, quickly escape and fragment the magma. The gases can come from the magma itself (igneous gases) or come from evaporating external ground or sea water (ph ... Entire entry

fissure vent

A chimney, flat, round, also known as a volcanic fissure or simply flat, round, is a linear volcanic chimney breaking through the lava.
A fissure vent, also known as a volcanic fissure or simply fissure, is a linear volcanic vent through which lava erupts, usually without any explosive activity. The vent is usually a few meters wide and may be many kilometers long. Fissure vents can cause large flood basalts and lava channels. This type of volcano is usually hard to recognize from the ground and from outer space because it has no ... Entire entry


Volcanology: volcanic passage
Exposed volcanic dike on Santorini (Greece)
Dikes are the mostly fissure-like, vertical routes of ascent of magma within the volcano. Many passages do not reach the surface, i.e. do not lead to eruptions, but to so-called intrusions, in which the magma slowly solidifies.
Dikes are imaginable as the veins of a volcano, the pathways of rising magma. A dike is called a - usually more or less vertical - flat, sheet-like magma body that cuts unconformingly through older rocks or sediments.

Most dikes can be described as fractures into which magma intrudes or from which they might erupt. The fracture can be caused by the intrusion of pressurized magma, or vice versa, ... Entire entry


View of the Santorini caldera, which dates back to before the Minoan eruption in 1613 BC. duration.
A caldera is created when a magma chamber is emptied after a major eruption and collapses. This can create a large - often water-filled - cauldron (= caldera).
A caldera is created when a magma chamber is emptied after a major eruption and collapses. This can create a large - often water-filled - cauldron (= caldera). Calderas are widespread in larger volcanoes. A caldera can fill up again over time through new volcanic eruptions.

Examples of calderas:
- Santorini in Greece
- Campi Flegrei Italy
- Crater ... full entry


Volcanology: Volcanic crater
Term for the deepening of the terrain, usually on the top of a volcano, which is created by the explosive ejection of lava from the sheet.
The word crater is of Greek origin. It goes back to the name for a bowl-shaped vessel that resembled the shape of the chimney of a volcano and was used to dilute heavy wine with water. Therefore, even today, simple house wine is referred to as "Krasi" in Greek. Entire entry

Lava bank

A lava bank in formation: active lava flows over a small beach, forming a solid cap.
A lava bank is a platform formed by new lava flows that extends the old shoreline; in particular, this can be seen in Hawaii at Kilauea volcano at times when lava enters the ocean and forms new land.
In their young stadium, benches are very unstable. They are often only underlain by loose material such as sand and wave-eroded rock. Young benches can collapse at any time, and standing on one is life-threatening. The bank can only be considered new stable land after a long time, when the pile of material under and in front of the bank is sufficiently stabilized. Entire entry

Lava trees

Lava trees on the Eastern Rift Zone of Kilauea Volcano, Hawaii
The lava coating around a tree trunk is left by an invading liquid lava flow.
When a liquid lava flow penetrates a forest, often, the lava flows around the larger trees, but does not tumble around their trunks. Upon very contact with the hot lava, the bark is a thin layer of lava sufficiently quenched to form an insulating coating around the trunk. The tree itself burns slowly in most cases, eventually falling down onto the lava.
The typical la ... Entire entry

Lava fountain

Lava fountain on Etna (June 24, 2001)
Water jets of liquid lava from an erupting vent, propelled by the expanding gases in the air.
Lava fountains are sustained jets of (usually very) liquid lava into the atmosphere. Lava fountains often occur on basaltic volcanoes such as Kilauea or Etna.
The well gains momentum from the expansion of the gas bubbles that dissolve from the magma as pressure falls as it rises in the conduit.
Heights, appearance, duration and broken volumes of lava fountains can vary greatly .... Entire entry


Molten rock inside a volcano or below the surface of the earth. Magma reaching the surface is called lava.


Skylight on Etna (Italy)
Skylights are openings into the roof over a lava tube from where the flowing lava stream can be seen. These holes are usually caused by the simple collapse of the roof of the pipe.


Obsidian from the Rocce Rosse lava flow on Lipari island (Italy)
Obsidian is a naturally occurring glass formed as an extrusive igneous rock. It is produced when Felsic lava extruded from a volcano cools rapidly through the glass transition temperature and freezes without sufficient time for crystal growth. Obsidian is commonly found within the margins of rhyolitic lava flows known as obsidian flows, where cooling of the lava is rapid. Because of the lack of cr ... Entire entry

Related entries (1):



Volcanology: Phreatomagmatic activity
Lava fountain on Etna during the 2001 eruption. The activity is phreatomagmatic in origin, which explains the large amount of ash involved in the well: the rising water on the way meets wet plains, where the contact between the water and magma produces violent fragmentation.
Volcanic activity where fresh magma and external water are involved.
Phreatomagmatic activity means erupting magma with external water, e.g. B. ground water, sea water, sea water, etc. reacts. In contrast, when only magma has erupted and gases only drifted into the magma originally contained, it is called igneous activity. When no magma erupts itself, but heated ground-water explosions and eruptions of older material run ... Entire entry

Smoke ring

Volcanology: volcanic gas ring, steam ring
Etna's Bocca Nuova crater in 2000, emitting smoke rings
A rare phenomenon where a visible vortex ring of gas and steam is excluded from a volcanic vent.
Under certain conditions, gas and steam displaced from a chimney can form gas stoves. It will likely require a specific Geolometric configuration of a circular vent exit as well as expelling gas into individual trains at just the right speed.
This phenomenon is very rare but has been seen on several volcanoes including Stromboli and Etna. On Etna w ... Entire entry


A type of highly viscous magma with high silicon content; It is found as a pumice stone (in airfall deposits or ignimbrites), lava, or obsidian. Rhyolite is also the name of the volcanic rock formed from rhyolite magma.

Shield volcano

Mauna Loa shield volcano (Big Island, Hawaii)
Volcanoes are volcanoes that are mostly fluid (usually basaltic) lava flows that are able to erupt, travel over great distances and so construct wide, gentle slopes over time. They are called volcanoes, because they resemble the shape of a warrior's shield.
Volcanoes are volcanoes that are mostly fluid (usually basaltic) lava flows that are able to erupt, travel over great distances and so construct wide, gentle slopes over time. They are called volcanoes, because they resemble the shape of a warrior's shield.
While stratovolcanoes, the other major morphological type of volcano, representative of most subduction t ... Entire entry

Cinder cone

Cinder cone at Mauna Kea Volcano, Hawaii. (Photo: P. Ong)
A volcanic cinder cone is formed during Strombolian eruptions and is conically shaped with its relatively steep slopes. It is made up of volcanic ash, slag and rock fragments.
A cinder cone is a conically shaped, tall cone with a crater that is formed during Strombolian eruptions. In such eruptions, lava is often ejected in fountains at a height of several hundred meters. The ejected lava particles often cool down in aerodynamic forms as bombs. The size of the ejected particles starts at several millimeters and can be me ... Whole entry

Related entries (4):

Etna - ash - bomb - breadcrust bomb

Mud volcano

Sidoarjo mud volcano (East Java)
Grjasewych's volcanoes are not real volcanoes, but openings that erupt mud, fine sediemtn of prezzurized water, steam and gas to escape deeper deposits is pushed up.
A mud volcano is a chimney erupting on the surface of mud and gas or steam, but not lava. Grjasewych's volcanoes are usually not the result of volcanic processes, but rather usually associated with environments where pressure deposits occur in the depths of this gas release, and steam that mixes with fine-grained sediments to form mud. The temperatures s ... Entire entry

Debris avalanche

A sudden collapse of volcanic material from an unstable side of a volcano. Debris avalanches are a particularly violent pyroclastic flow (in the broader sense).


From the Latin "tumulus" = "little hill", tumuli (pl.) Are raised areas of pahoehoe lava crust caused by pressure from still liquid lava to accumulate under the hardened crust.
Burial mounds are a characteristic feature of all Pahoehoe Lava Flow fields, such as B. Kilauea volcano, Hawaii, but also many other basaltic volcanoes Etna including celebrities. Entire entry


Volcanology: Volcanic ash advice center
Coverage of the globe from the 9th VAAC.
Volcanic Ash Advisory Centers (VAAC) are research centers that monitor volcanic ash clouds in real time. Every time a volcano breaks a significant cloud of ash, brief reports are issued and transmitted directly to the air control centers. The 9 VAAC are located in London, Toulouse, Tokyo, Darwin, Anchorage, Washington, Montreal and Buenos Aireas and collectively cover most of the world.
The Volcanic Ash Advisory Centers (VAAC) are groups of government funded bodies that monitor volcanic ash clouds around the world in real time. Europe experienced in April 2010 volcanic ash clouds are dangerous for planes and must be avoided to fly through, even if that means flight cancellation.

As of 2010 there are 9 VAAC located in different area ... Entire entry


The possibility of a liquid flowing. Basalt magma has a relatively low viscosity, hence runny, while rhyolite magma has a high viscosity making the magma thick and sticky.


The science of studying volcanoes.
Volcanology comprises the study of volcanoes and volcanic phenomena and is mostly considered a sub-part of geology, but is intertwined with other science disciplines such as: chemistry, physics, but also sociology, history, archeology. Entire entry

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