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Rosario and Ines in the Grotta dei Lamponi - one of the largest lava tubes of Etna (Photo: Tom Pfeif...
Fuego volcano in the first morning light (Photo: Tom Pfeiffer)
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Ash plume from an explosive eruption at Etna volcano (Italy)
Snow and ash from Hekla volcano's eruption in 2000
Ash emission from Etna' s NE crater (in 1999)
Ash deposits from numerous, turbulent pyroclastic flows during the Minoan eruption of Santorini volcano, Greece.
Volcanic ash is the term for all fine-grained volcanic products (smaller than 2 mm), normally magma or older rock fragmented during explosive eruptions.
Volcanic ash has nothing to do with fire, but is a mere definition of grain-size. Ash can range in size from sandy to extremely fine; any fragment ejected by a volcano less than 2 mm in diameter is called ash. It may consists of freshly ejected lava (usually turned into a glass shard because of rapid cooling), older fragmented rock, or small crystals.
Ash is produced by explosive activity when expanding gas fragments other material (uprising lava, surrounding rock). The more explosive an eruption, the more ash is usually produced. Hot ash can easily mix with air and erupted gasses and then form an eruption column. If the eruption column is buoyant it will rise to tens of km into the atmosphere during violent eruptions. These ash clouds can then be carried hundreds and thousands of km by wind, even circle the entire hemisphere for a few years before the finest particles are washed out. Ash-loaded eruption columns can also become too dense to rise vertically; instead, they will then collapse to form (usually hot) avalanches, so-called pyroclastic flows.
It is very common to observe that ash particles stick together to form small aggregates, so-called accretionary lapilli, enabling the ash to deposit because of the dramatically increased fall velocity of the aggregate.
Volcanic ash is a serious hazard to life and property; it can cause breathing problems, heavy ash loads on buildings cause the roofs to collapse. Ash plumes in the atmosphere threaten air traffic seriously, because ash even in small concentrations can disable jet engines.
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Popocatépetl Volcano Special
: The activity of Mexico's most active and largest volcano has been picking up gradually during the past months. If you like to join a small group of volcano enthusiasts, join us, stay 5 nights near the volcano and move around for extended day- and night-time observation.
Volcano Special Tours
: We organize tours to particularly active volcanoes and during ongoing eruptions for extended observation time from various viewpoints. These trips, exclusively for very small groups, are often announced only at short notice and require fast travel and flexibility. Each trip is accompanied by a volcanologist from our team. Examples include: Kilauea (Hawai'i), Colima (Mexico), Krakatau and many others.