CRATERS of the MOON General Management Plan

APPENDIX C:

aa lava flow: A lava flow that has a rough, jagged surface with many sharp points. Literal meaning of this Hawaiian word is "hard on the feet."

cinder cone: A relatively steep-sided cone built of small fragments of volcanic material that spewed from a vent and fell back into a pile. Because the loosely packed fragments are rather permeable, water runs through the cinders rather than eroding away the cones.

collapse depression: A basin-shaped volcanic depression caused by the collapse of the roof of a lava tube. Some depressions may be more than a hundred feet in diameter.

eruption: The emission or ejection of volcanic materials. In central eruptions, volcanic materials are emitted from a central vent or pipe and ordinarily form a volcanic cone; in fissure eruptions, lava or pyroclastic materials emanate from a relatively narrow fissure, generally building lava plains and plateaus. Craters of the Moon's features resulted from fissure eruptions.

fissure: An extensive crack, break, or fracture in the earth's crust. An eruptive fissure is one from which volcanic products issued.

kipuka: An island of vegetation that has developed on the top of an old lava flow that is surrounded by newer flows but has not been covered by a more recent lava flow.

lava bomb: A fragmentary piece of volcanic material that was liquid at the time of ejection. The soft lava bomb tumbles and spins as it flies, acquiring a characteristic twisted tear shape. Most lava bombs have surface markings acquired during flight through the air or after landing. Also called "volcanic bomb."

lava tube: A flow channel through which liquid lava moved while the upper surface hardened. When fluid molten lava flowed out of the ground, it behaved like a stream of water working its way downhill. Soon the surface cooled and hardened, forming a crust that insulated the molten lava inside, enabling it to remain liquid. The molten inside lava eventually flowed out, leaving the crust as the walls of a lava tube. A tube may have collapsed sections or skylights where only the ceiling has collapsed. The inside diameter of lava tubes found in Craters of the Moon varies from a few feet to 50 feet.

pahoehoe lava flow: A smooth, billowy, or ropy appearing lava flow that resulted from a more fluid flow than that which caused aa lavas (pahoehoe means "ropy" in Hawaiian). Its formation process can be described as "hardening like fudge poured from a pan." A continued flow of pahoehoe lava may break the twisted surface into blocks. The rough, jagged blocks resemble aa lava but do not have the sharp surface projections and spines characteristic of aa.

pressure ridge: An elongated ridge formed by viscous lava pushing upward.

rafted block: Large fragment of crater broken off and carried to another location by flowing lava.

spatter cone: A low, steep-sided hill or mound that formed when clots of pasty lava stuck together as they fell, forming a cone around the volcanic vent. The spatter cones in Craters of the Moon are generally less than 100 feet tall.

squeezeup: A lava ridge that results from lava pushing up through existing cracks.

tree mold: A hollow cast of a tree formed when molten lava encased a tree and then hardened.

volcanic bomb: See lava bomb.

volcanic rift zone: A concentration of volcanic landforms and structures along a linear zone of cracks in the earth's crust.

volcanic vent: An opening in the earth's crust through which volcanic materials are erupted.

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