Get our newsletter!
Try our free app!
: "One of the most eye-catching guides to the world’s volcanoes ever published.
Our expert volcanologists and photographers offer unique travel experiences: volcano expeditions
, photo tours, and relaxed walking & study tours.
: spaces available / : guaranteed / : few spaces left / : booked out
Generally, acceleration is increase of speed or velocity. During earthquakes, the shaking of ground is a swinging motion involving both acceleration and deceleration.
Its maximum value is the largest increase in velocity recorded at a particular point. It largely influences how damaging an earthquake is in this area.
Accretionary lapilli in an ash deposit on Santorini.
Small spherical balls of volcanic ash
Accretionary lapilli are small spherical balls of volcanic ash that form from a wet nucleus falling through a volcanic ash cloud. They can flatten on hitting the ground or may roll on loose ash and grow like a snowball. -> See whole entry
Aftershocks following the M6.5 quake in Idaho on 31 Mar 2020
Aftershocks are smaller quakes that follow a usually larger earthquake in the same rupture zone. The can occur up to weeks, months or even years after, depending on the size of the main shock.
Aftershocks are smaller than the mainshock and occur within 1-2 rupture lengths distance from the mainshock.
In general, the larger the mainshock, the larger and more numerous the aftershocks, and the longer they will continue. Large earthquakes can be followed by thousands of aftershocks.
The larger aftershocks following an earthquake can be particularly dangerous if many structures have been ... -> See whole entry
Agate is a microcrystalline variety of quartz (silica), chiefly chalcedony, characterised by its fineness of grain and brightness of color.
Agate is a microcrystalline variety of quartz (silica), chiefly chalcedony, characterised by its fineness of grain and brightness of color. Although agates may be found in various kinds of rock, they are classically associated with volcanic rocks but can be common in certain metamorphic rocks.
Colorful agates and other chalcedonies were obtained over 3,000 years ago from the Achates River, now ca... -> See whole entry
Typical andesite from the Methana peninsula (Greece)
Andesite is a gray to black volcanic rock with between about 52 and 63 weight percent silica (SiO2). Andesites are typical for lava domes and stratovolcanoes.
Andesite is an igneous, volcanic rock, of intermediate composition, containing between about 52 and 63 weight % silica (SiO2).
Andesites contain crystals composed primarily of plagioclase feldspar and one or more of the minerals pyroxene (clinopyroxene and orthopyroxene) and lesser amounts of hornblende. At the lower end of the silica range, andesite lava may also contain olivine. Andesite magma ... -> See whole entry
Volcanology: volcanic ash
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 ex... -> See whole entry
Volcanology: volcanic ash fall
Volcanic ash fall is the deposition of ash from the air from eruption plumes emitted during explosive volcanic eruptions.
Related keywords (1): ash
The uppermost viscous layer of the mantle where pressure and temperature conditions can allow partial melting of the mantle rocks, which forms magmas.
From the Greek "asthenos"=weak and "sphera"=sphere, the asthenosphere is the uppermost layer of the plastic, highly viscous mantle beneath the brittle crust. It extends to depths of 100-200 km.
Because the pressure in this zone is still comparably low while temperature is high, parts of the mantle rocks can be in a molten state and form magmas. This happens especially in areas where pressure is ... -> See whole entry
More on VolcanoDiscovery
Ambrym+Yasur volcanoes in Vanuatu
: An adventurous expedition to some of the most spectacular and active volcanoes in the world! Our volcano expedition to Vanuatu lets you spend 1 week on Ambrym with its multiple active lava lakes and 4 days on Yasur, famous for its spectacular fireworks. Guided by professional volcanologist, small groups (May-Sep).
Excellent information for anyone wishing to visit and enjoy active volcanoes safely. Detailed guidelines to 42 different volcanoes around the world.
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.
: Guatemala - a land of volcanoes and the colorful Mayan culture with incredible variety. A dream destination for volcano enthusiasts and photographers!