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Geology glossary

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hauyn

Minerals: hauyn crystals
Hauyn crystals from the German volcano Laacher See (photo: Stefan Wolfsried)
Hauyn crystals from the German volcano Laacher See (photo: Stefan Wolfsried)
Hauyn is a blue mineral, found f.e. in the pumice of the Laacher See eruption in Germany
Hauyne, haüyne or hauynite is a tectosilicate mineral with sulfate and chloride with formula: (Na,Ca)4-8Al6Si6(O,S)24(SO4,Cl)1-2. It is a feldspathoid and a member of the sodalite group. Hauyne crystallizes in the isometric system forming translucent, vitreous typically twinned crystals with highly variable color (blue, white, grey, yellow, green, pink). It has a Mohs hardness of 5 to 6 and a spec... -> See whole entry

Hawaiian eruption

Volcanology
Lava fountain more than 1,000 ft tall from Mauna Ulu, a vent of Kilauea Volcano in Hawaii, on 22 Aug 1969, a spectacular example of a Hawaiian eruption. Photo by D.A. Swanson, HVO / USGS
Lava fountain more than 1,000 ft tall from Mauna Ulu, a vent of Kilauea Volcano in Hawaii, on 22 Aug 1969, a spectacular example of a Hawaiian eruption. Photo by D.A. Swanson, HVO / USGS
During a Hawaiian eruption, very fluid, basaltic lava is erupted from the vent as lava fountains and forms lava flows. The fountains are driven by the expanding gasses that were contained in the magma and leave the vent as a jet. Such eruptions are common for hot-spot volcanoes such as Kilauea on Hawai'i.
The lava fountains can reach heights of several hundreds meters, sometimes even more than 1 km. They can last for hours or even days and often occur from fissure vents to form so-called curtains of fire.

The lava spatter that falls back from the fountain can form lava flows if it is still fluid enough, or build up welded spatter ramparts and cinder cones around the vent. Along with the lava foun... -> See whole entry

hornito

Volcanology
Erupting hornito on Kilauea volcano (Hawaii)
Erupting hornito on Kilauea volcano (Hawaii)
Erupting hornito on Etna volcano (Italy)
Erupting hornito on Etna volcano (Italy)
Hornito (Spanish) = "Little oven".

Volcanic hornitos are small (usually a few meters high) rootless spatter cones that form on the surface of a (usually basaltic pahoehoe) lava flow. A hornito develops when lava is forced up through an opening in the cooled surface of a flow (a skylight) and then accumulates around the opening. Typically, hornitos are steep sided and form conspicuous pinnacles o... -> See whole entry

hypocenter

Earthquakes
Epicenter and hypocenter of an earthquake (Source: USGS earthquake glossary)
Epicenter and hypocenter of an earthquake (Source: USGS earthquake glossary)
When talking about earthquakes, the hypocenter or focus is the point inside the earth where an earthquake rupture starts. It is often confused with epicenter, which is the is the point directly above it at the surface of the Earth, where the quake is usually felt most strongly.

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