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Volcano Calendar 2019
: We're proud to present our 2019 volcano calendar: 13 different and attractive images of volcanoes, volcanic landscapes and phenomena taken during volcano tours over the past few years.
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Illustrated Volcano Glossary
Volcanology: pumice stone
Our tour guide Marta posing in Lipari's pumice...
Pumice from the Greek island Santorini
Pumice is a very light, porous volcanic rock that forms during explosive eruptions. During the eruption, volcanic gases dissolved in the liquid portion of verz viscous magma expand very rapidly to create a foam or froth; the liquid part of the froth then quickly solidifies to glass around the gas bubbles.
The volume of gas bubbles is usually so large that pumice is lighter than water and floats.
Pumice is an important industrial mineral used to produce high-quality cement and lightweight, isolating building materials.
Pumice is a textural term for a volcanic rock that is a solidified frothy lava composed of highly microvesicular glass pyroclastic with very thin, translucent bubble walls of extrusive igneous rock. It is commonly, but not exclusively of silicic or felsic to intermediate in composition (e.g. rhyolitic, dacitic, andesite, pantellerite, phonolite, trachyte), but occurrences of basaltic and other compositions are known. Pumice is commonly pale in color, ranging from white, cream or grey, but can be green brown or black. It forms when gases exsolving from viscous magma nucleate bubbles which cannot readily decouple from the viscous magma prior to chilling to glass. Pumice is a common product of explosive eruptions (plinian and ignimbrite-forming) and commonly forms zones in upper parts of silicic lavas. Pumice has an average porosity of 90%, and initially floats on water.
Scoria differs from pumice in being denser, with larger vesicles and thicker vesicle walls; it sinks rapidly. The difference is the result of the lower viscosity of the magma that formed scoria. When larger amounts of gas are present, the result is a finer-grained variety of pumice known as pumicite. Pumice is considered a glass because it has no crystal structure. Pumice varies in density according to the thickness of the solid material between the bubbles; many samples float in water. After the explosion of Krakatoa, rafts of pumice drifted through the Pacific Ocean for up to 20 years, with tree trunks floating among them. In fact, pumice rafts disperse and support several marine species. In 1979, 1984 and 2006, underwater volcanic eruptions near Tonga created large pumice rafts, some as large as 30 km that floated hundreds of miles to Fiji.
Famous pumice deposits in Europe include Lipari Island (Italy), Santorini and Yali (Greece), as well as the Laacher See (Germany).
More on VolcanoDiscovery:
Volcano Calendar 2018
: We're proud to present our 2018 volcano calendar: 13 different and attractive images of volcanoes, volcanic landscapes and phenomena taken during volcano tours over the past few years.
From Krakatau to Bali
: Visit Java's famous volcanoes: Krakatau, Merapi, Bromo, Semeru, Ijen and others, crossing Java from west to east. This study and photography trip for a small exclusive group is one of our classic and best tours.