Illustrated Volcano Glossary

ash

Volcanology: volcanic ash
Ash plume from an explosive eruption at Etna volcano (Italy)
Ash plume from an explosive eruption at Etna volcano (Italy)
Snow and ash from Hekla volcano's eruption in 2000
Snow and ash from Hekla volcano's eruption in 2000
Ash emission from Etna' s NE crater (in 1999)
Ash emission from Etna' s NE crater (in 1999)
Ash deposits from numerous, turbulent pyroclastic flows during the Minoan eruption of Santorini volcano, Greece.
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.

Related keywords (4):

ashfall - explosive - pyroclastic flow - VAAC
Try our free app!
Volcanoes & Earthquakes - new app for Android
Android | iOS version

More on VolcanoDiscovery

Why is there advertising on this site?
Support us - Help us upgrade our services!
We truly love working to bring you the latest volcano and earthquake data from around the world. Maintaining our website and our free apps does require, however, considerable time and resources.
We need financing to increase hard- and software capacity as well as support our editor team. We're aiming to achieve uninterrupted service wherever an earthquake or volcano eruption unfolds, and your donations can make it happen! Every donation will be highly appreciated. If you find the information useful and would like to support our team in integrating further features, write great content, and in upgrading our soft- and hardware, please make a donation (PayPal or Online credit card payment).

Planned features:
  • Weather reports
  • Tsunami alerts
  • Design upgrades
  • Faster responsiveness
Thanks to your past donations, these features have been added recently:
  • Earthquake archive from 1900 onwards
  • Additional seismic data sources
  • Improved content in English
Download and Upgrade the Volcanoes & Earthquakes app to get one of the fastest seismic and volcano alerts online:
Android | IOS
Thank you!
Copyrights: VolcanoDiscovery and other sources as noted.
Use of material: Most texts and images, in particular photographs, on this website are protected by copyright. Further reproduction and use of without authorization is usually not consented. If you are not sure or need licensing rights for photographs, for example for publications and commercial use, please contact us.