**Bomb:** A pyroclast with a diameter greater than 64 mm (2.5 inches)
that has a rounded or ellipsoidal shape that indicated that it was
wholly or partially molten condition during eruption or flight. The
shapes of bombs are determined largely by the viscosity of flight, and
rates of cooling, and deformation upon impact.

> [Spindle Bomb]{.underline}: Almond-shaped bombs that result from the
> tearing apart of ribbons of lava either during flight or upon impact.

[Ribbon Bomb]{.underline}: Elongated ropy-shaped bombs.

[Cowdung Bomb]{.underline}: Very fluid bombs which flatten or splash
upon landing.

> [Cored Bombs]{.underline}: Bombs with a nucleus of solid material. The
> solid core may be fragments of previously solidified magma from the
> volcano, or xenoliths from either the crust or the mantle.
>
> [Breadcrust Bomb]{.underline}: Bombs with a fractured surface from a
> quickly quenched crust that was a fractured by continued expansion of
> vesicles in the molten core. Most bread crusting form after landing.
> Breadcrust bombs are usually andesitic in composition.

**Caldera:** A very large crater with a diameter greater than 1 km.
Calederas usually result from ground surface collapse into a magma
chamber momentarily emptied from an extrusion of a great amount of
volcanic material.

**Cinder:** A small nut-size to fist-size, or larger, piece of red or
black highly vesicular lava that cooled in air during flight after
eruption from a vent.

**Crater:** A bowl-shaped depression in the summit of a volcano which
lies directly above the vent from which volcanic material is ejected.
Craters are usually formed by the explosivity of the volcanic eruption.

**Extrusive** or **volcanic:** formed by the solidification of lava
(magma which has been erupted on the Earth\'s surface)

**Igneous:** formed from cooling and solidification of magma

**Intrusive** or **plutonic:** formed by solidification of magma below
the Earth\'s surface

**Lava:** Magma that has reached the Earth\'s surface.

**Magma:** Molten rock material which may include suspended solids (such
as crystals or rock fragments) plus dissolved gases. Magma may have a
range of compositions, is characterized by high temperatures, and has
the properties of a liquid. Magma may be erupted as a **lava** or as
**pyroclasts.**

**Metamorphic:** formed by recrystallization of a pre-existing rock
(without melting) at high temperatures and pressures.

**Plate Tectonics:** Is a special branch of tectonics that studies the
processes by which the lithosphere mores above the convecting
asthenosphere. The asthenosphere convects because of a large temperature
difference between the Earth\'s hot interior and it\'s cool surface.
This difference sets up convection currents as the hot mantle rises,
cools near the surface, then sinks. The brittle lithosphere is broken
into a mosaic of plates, which ride on the convecting asthenosphere.

**Sedimentary:** formed by chemical precipitation of or by cementation
of sediment **Volcano:** (1) The vent from which magma, gases, and
fragmental material are erupted from the Earth\'s interior. (2) The
edifice formed around a volcanic vent.

**Tectonics:** Is the study of the large structures of the Earth\'s
crust and the processes that formed them.

[Types of Eruptions]{.underline}:

**Gas**: Eruptions of gas with no accompanying solid materials.

> **Hawaiian**: Non-explosive eruptions of gusher-like lava fountains
> (\"fire fountains\") that generate red-hot lava rivers of very fluid
> basaltic lavas.

**Strombolian**: Moderately explosive eruptions of basaltic magma with
moderate gas content. (Capulin Volcano)

> **Vulcanian**: Moderately explosive, intermittent eruptions that
> produce moderate ash columns. More explosive than Strombolian.

**Pelean**: Explosive collapse of a silicic lava dome which produces
pyroclastic.

> **Plinean**: Extremely explosive eruptions that produce ash columns
> that extend many tens of miles into the atmosphere, and produce
> widespread deposits of fallout ash, and may produce pyroclastic flows.
>
> **Hydrovolcanic**: Violently explosive eruptions driven by the steam
> explosions produced by the interaction of surface water or shallow
> groundwater with hot magma.

[Types of Volcanoes]{.underline}:

**Cinder Cone**: Capulin Volcano. Strombolian type eruption.

**Composite Volcano**: Mt. St. Helens. Plinean, Pelean, Vulcanian type
eruption.

**Shield Volcano**: Hawaii Volcanoes. Hawaiian type eruption.

**Vent:** The opening at the Earth\'s surface through which volcanic
material are extruded. Also, the channel or conduit through which
volcanic material pass on its way to the surface.

**Volcanic Eruption:** An expulsion of gases, fragmental material,
and/or molten lava from beneath the ground through a vent into the
atmosphere.

\*Definitions taken from \"Volcanology for Interpreters\" Mathis, A.
1999