Geology 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.

Intraplate refers to the location of an event (e.g. an earthquake) in the interior of a tectonic plate.

Intraplate quakes occur within a tectonic plates, sufficiently far from its margins not to be affected or directly caused by the generally more active processes that are taking place along the plate boundaries (subduction, spreading, or transform movments between two plates).
Intraplate quakes are typically the result of releasing long-term accumulated stress in the interior of the crust along ac... Read all

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Molten rock, called magma, is called lava when it reaches the surface during a volcanic eruption. Depending on how the magma erupts, it can form lava flows, lava fountains, lava lakes, or be fragmented into scoria and ash during explosive eruptions.

In a wider use of the term, also the cooled and solidified products of erupted magma are called lava (in form of coherent lava flows, or fragmented tephra).

Magma when it erupts as lava is almost never a completely molten rock, but contains 3 phases: liquid, solid mineral crystals (xenoliths) and gas bubbles, mainly water and carbon dioxide.
The temperature of erupted lava ranges from around ... Read all

Lava balloons are hollow gas-filled pieces of lava floating to the surface above effusive submarine vents. Many lava balloons have been produced and observed during the ongoing 2011-12 shallow submarine eruption at El Hierro.

Floating lava blocks could result from the detachment of pillow-lava edges followed by the ascent of blocks with sufficient gas content. It is also possible that hot, gas-rich lava fragments result from small submarine lava lakes or fountains.
A thin frozen skin of lava seals the gas cavity, and the block might then rise as a hot lava balloon. During ascent, the gas exsolves and nucleates inside ... Read all

A lava bench is a platform formed by new lava flows that extends the old shoreline; in particular, this can be observed on Hawaii at Kilauea volcano during times when lava is entering the ocean, forming new land.

In their young stadium, benches are highly unstable. They often are underlain only by loose material such as sand and wave-eroded rock. Young benches can collapse at any time, and it is life-threatening to stand on one. Only after a long time, when the pile of material under and in front of the bench is sufficiently stabilized, the bench can be considered new stable land. Read all

Lava domes are accumulations of highly viscous lava above or near the vent(s) where they were erupted during slow flow, like a sticky glue squeezed out or oozing out from a hole in its container.
Lava domes often take the form of a rounded hill, resembling a dome, but come in many other shapes as well.

Lava domes are very similar to thick lava flows, with the difference being that the lava once erupted from the vent almost doesn't flow at all, and piles up above the vent instead of flowing away downhill or to the side. In fact, there is a transition between thick, sticky lava flows and lava domes, depending on how viscous the lava is, how steep the terrain, the flow rate and other factors. Somet... Read all

Lava flows are almost self-explanatory. When magma is erupted in molten or a partially molten state it often has the ability to flow. This is typically the case for basaltic volcanoes such as Hawaii and Etna whose lavas are relatively fluid. Lava flows might form either as primary flows directly flowing out of a vent from the vent or by rapid aggregation of hot fluid spatter that fall back from lava fountains to form a flow.

The appearance of lava flows can vary greatly with chemistry, flow rate, strain rate, temperature, viscosity and other factors. The most simple division can be made between aa lava that usually has a blocky appearance, since the surface of the flow breaks into spiny or blocky pieces, and pahoehoe lava flows, which form a smooth surface and often produce spectacular ropy textures. Read all

Jets of fluid lava propelled into the air from an erupting vent, driven by expanding gasses.

Lava fountains are sustained jets of (usually very) fluid lava into the atmosphere. Lava fountains occur commonly on basaltic volcanoes such as Kilauea, or Etna.
The fountain gains its momentum by the expansion of gas bubbles that dissolve from the magma as pressure falls while it is rising in the conduit.
Heights, appearance, duration and erupted volumes of lava fountains can vary greatly. St... Read all

Lava lakes are accumulations of larger volumes of liquid lava above one or several vents, usually contained within a crater on the summit of the volcano.

Volcanoes with eruptions that produce long-lasting lava lakes are relatively rare; some volcanoes are famous for their lava lakes: Kilauea (Hawaii), Erta Ale (Ethiopia), Nyiragongo (at present probably the most violent lava lake in the world, about 120 meters wide), Ambrym volcano (Vanuatu), Mt Erebus (Antarctica) and a few others with sometimes smaller lakes. Read all