HAWAII NATURE NOTES
THE PUBLICATION OF THE
NATURALIST DIVISION, HAWAII NATIONAL PARK
AND THE HAWAII NATURAL HISTORY ASSOCIATION

VOLCANIC VOCABULARY

Aa—lava with rough clinkery surface.

Andesite—a lava generally of lighter color than basalt and richer in silicon and sodium.

Ash—fine-grained volcanic ejecta, of sand or dust size.

Augite—a variety of the mineral pyroxene containing aluminum.

Basalt—a dark heavy lava rich in iron and magnesium and comparatively poor in silicon; the common lava of Hawaii.

Blocks—volcanic ejecta larger than 1-1/2 inches across, solid when thrown out.

Bombs—volcanic ejecta, molten when thrown out, larger than 1-1/2 inches across.

Caldera—a large depression formed by sinking in of part of the mountain top.

Cinder cone—a cone-shaped hill built by ejecta around a volcanic vent.

Crater—a bowl-shaped depression, generally in the top of a volcanic cone.

Dike—a sheetlike body formed by molten rock soldifying in a crack.

Ejecta—fragments thrown out by volcanic explosion.

Epicenter—the point on the earth's surface directly above the place of origin of an earthquake.

Epimagma—a semisolid lava resembling aa in appearance.

Fault—a fracture in the earth's crust along which one side has moved with respect to the other.

Fault scarp—a cliff formed by movement on a fault.

Feldspar—a light-colored mineral composed largely of silicon, oxygen, aluminum, and varying proportions of calcium, sodium, and potassium.

Fumarole—a hole from which volcanic gases issue.

Igneous rocks—rocks formed by solidification of molten rock.

Intrusive rock—a rock formed by magma solidifying beneath the earth's surface.

Kipuka—an "island" of old land left within a lava flow.

Lava—hot liquid rock at or close to the earth's surface, and its solidified products.

Lithic—stony.

Magma—hot liquid rock.

Lapilli—volcanic ejecta from about 1/4 to 1-1/2 inches across.

Olivine—a green mineral composed largely of silicon, iron, magnesium, and oxygen.

Pahoehoe—lava with smooth or ropy surface.

Pele's hair—volcanic glass spun out into hairlike form.

Pele's tears—congealed lava droplets.

Phreatic—resulting from ground water, like the steam explosions of Kilauea in 1924.

Pigeonite—a pyroxene resembling augite but containing more iron.

Pisolite—in volcanology, a small mud-ball, generally about the size of a pea, formed by raindrops falling through a cloud of volcanic ash.

Pit crater—a crater formed by sinking in of the surface; not primarily a vent for lava.

Plagioclase—a feldspar containing lime and soda but little potash.

Pumice—a froth of volcanic glass.

Pyromagma—a fluid highly gas-charged very hot lava.

Pyroxene—a group of dark-colored minerals composed largely of silicon, magnesium, iron, and oxygen.

Rift—a fracture in the earth's crust.

Rift zones—the highly fractured belts on flanks of volcanoes along which most of the eruptions take place.

Scoria—slaggy porous ejecta.

Shield volcano—a volcano having the shape of a very broad, gently sloping dome.

Solfatara—a fumarole liberating sulfur-bearing gas.

Spatter cone—a cone built by spattery ejecta around a vent.

Talus—rock fragments that accumulate in a heap at the foot of a cliff.

Vent—au opening where volcanic material reaches the surface.

Vesicular—having bubble-holes formed by gases.

Vitric—glassy.