Glossary of Technical Terms Related to the Ice Age Floods
This glossary was prepared by the Ice Age Floods Institute to help people of all backgrounds understand the geologic terms used to explain phenomena related to the Ice Age Floods. For links to other glossaries available on the Web, visit the Links section of the Resources page. NOTE: Terms marked with an asterisk (*) are defined elsewhere in the glossary.
basalt - A dark igneous* volcanic rock composed of primarily two minerals: plagioclase and pyroxene. Over a period of 11 million years (17 to 6 million years B.P.) hundreds of flows of Columbia River basalt were extruded from long; linear vents in southeastern Washington; northeastern Oregon and west-central Idaho and traveled for hundreds of miles before cooling and solidifying to form the Columbia Plateau.
bedrock - A general term for the rock (e.g.; basalt*) that underlies the soil or other unconsolidated; surficial material.
butte - A conspicuous; isolated; generally flat-topped hill with relatively steep side slopes; often capped by a more resistant layer of rock and bordered by talus*. Often represents an erosional remnant; smaller in extent than that of a mesa*; carved from flat-lying rocks.
Channeled Scabland - An eroded; interconnected network of streamlined loess* islands; flood channels; coulees*; cataracts; and plunge pools* scoured into basalt* by cataclysmic floods in eastern Washington State. These features are unique to this region of the Earth; however they are similar to channel networks observed on Mars.
clast - An individual particle or fragment of a sediment or rock produced by the mechanical weathering of a larger rock mass.
clastic dike - A feature that cuts across bedding structures and is composed of the sedimentary* material it transects. Believed to be the result of fracturing and sediment movement due to earthquake shaking during or soon after cataclysmic flooding.
clay - Extremely small sedimentary* particles that are less than 0.004 mm in diameter.
coarse-grained - Pertains to sedimentary* material composed of relatively large particles of sand* and/or gravel*.
columnar basalt - Thick lava flows commonly appear to be comprised of vertical honeycomb-like columns of basalt. Linear joints form in the rock as it cools. They define the columns and generally form perpendicular to the cooler bounding surfaces above and below. In cross section the resulting joints are often six-sided (an optimum packing geometry) but may be anywhere from 3-sided to nearly round. Because of the through-going joining; columns are relatively easily broken out of a rock face by hydraulic plucking and ice-wedging.
coulee - A long; dry; steep-walled; trench-like gorge or valley representing an abandoned river channel. In south central Washington; the term coulee is mostly used for an abandoned ice-age flood channel.
eolian - Pertaining to the wind. Includes deposits of loess* and dune sand*.
erratic - An erratic is a piece of rock that differs from the size and type of rock native to the area in which it rests. implying it has been transported and deposited at some distance from the outcrop from which it was derived and generally associated with transport by glacial ice or icebergs..
flood bar - An accumulation of sediment; most often composed of sand* and/or gravel*; that occurs along flood routes where the currents move slower for various reasons. Different types of flood bars include eddy bars; expansion bars*; shoulder bars; and pendant bars*.
fore-set bedding - Primary sedimentary* structure in flood gravels where a pronounced dip occurs in bedding planes in the direction of sediment transport.
giant current ripples (GCRs) - Giant current ripples are active channel topographic forms up to 20 m high, which develop within cemtral flow areas of the main outflow valleys created by glacial lake outburst floods. Giant current ripple marks are extremely large analogs of small current ripples formed in sandy stream sediments. Giant current ripples are important diagnostic depositional features in plains and scablands associated with massive floods.
Glacial Lake Missoula - The source for most or all of the floodwater that created the Channeled Scabland* of eastern Washington. The lake formed behind an ice dam in the Idaho Panhandle that periodically failed; sending torrents of water downstream. At its maximum; Lake Missoula contained 600 cu. mi. of water; was 2;000 ft deep; 200 miles long; and covered an area of 3;000 sq. mi. It took up to 125 years to fill but only 2 to 3 days to completely empty.
granitic - Pertaining to granite; a general term for any light-colored igneous* rock that formed deep underground within a cooling body of liquid magma.
granodiorite - A type of granitic* rock consisting of mostly crystalline quartz and plagioclase feldspar.
gravel - Large sedimentary* particles that are greater than 2 mm in diameter. Gravel clasts* include; in increasing size; granules; pebbles; cobbles; and boulders.
hanging valley - A tributary valley whose floor is notably higher than the valley it joins. Characteristic of flood coulees*; where flat valley floors suddenly drop off abruptly at one or both ends where they join adjacent coulees.
Holocene Epoch - The period of geologic time since the last Ice Age (10;000 years ago to the present).
hydraulic constriction - Where a large volume of water is confined to a narrow opening. If more water enters the opening than can drain through; then the constriction will cause water to back up; creating a type of hydraulic dam.
Ice Age - The last glacial period is popularly known as the Ice Age, and was the most recent glacial period within the Quaternary glaciation occurring during the last 100,000 years of the Pleistocene, from approximately 110,000 to 12,000 years ago. Scientists consider this "ice age" to be merely the latest glaciation event in a much larger ice age, one that dates back over two million years and has seen multiple glaciations. During this period, there were several changes between glacier advance and retreat. The Last Glacial Maximum, the maximum extent of glaciation within the last glacial period, was approximately 22,000 years ago
igneous - Rock that solidified from molten or partly molten material (i.e.; magma). One of the three principal rock types; along with sedimentary* and metamorphic*.
Kolk - An underwater vortex created when a rapidly rushing current of water passes an underwater obstacle in boundary areas of high shear. High velocity gradients produce a violently rotating column of water; essentially a high energy whirlpool; that can pluck multi-ton rocks from the underlying bed of the current. A Kolk is usually relatively stationary due to the factors that create it; and is the mechanism that created Kolk ponds during the Floods.
Lake Bonneville - An Ice-Age lake that formed in central Utah from melting mountain glaciers. The Great Salt Lake today is a much smaller remnant of Lake Bonneville. The lake drained catastrophically only once; toward the end of the Ice Age about 15;000 years ago when the lake overtopped a drainage divide and partially drained northward into the Snake River.
Lake Lewis - A temporary lake that formed behind the hydraulic constriction* at Wallula Gap*. Within 5 days or less the lake grew to an elevation of 1;250 ft above sea level before completely draining through the gap over a period of several days.
lithology - The physical character of a rock; including its color; mineralogic composition; and grain size.
loess - Windblown silt* and fine sand* that collects on the lee sides of ridges at higher elevations within the Pasco Basin.
maar - A broad, low-relief volcanic crater caused by an eruption when groundwater comes into contact with hot lava or magma. Maars are shallow, flat-floored craters that scientists interpret as having formed above a volcanic pipe as a result of a violent expansion of magmatic gas or steam. Most maars have low rims composed of a mixture of loose fragments of volcanic rocks and rocks torn from the walls of the diatreme.
magnetic polarity shifts - A change in a planet's magnetic field such that the positions of magnetic north and magnetic south are interchanged. The Earth's field has alternated between periods of normal polarity, in which the direction of the field was the same as the present direction, and reverse polarity, in which the field was the opposite. The time spans are randomly distributed with most being between 0.1 and 1million years with an average of 450,000 years. Most reversals are estimated to take between 1,000 and 10,000 years.
mesa - An isolated; nearly level land mass standing distinctly above the surrounding country; bounded by abrupt steep-sided slopes on all sides and capped by layers of more-resistant rock.
metamorphic - Any rock derived from pre-existing rocks by mineralogical; chemical; and/or structural changes. One of the three principal rock types; along with sedimentary* and igneous*.
Miocene Epoch - The period of geologic time between 5 and 24 million years before the present; when Columbia River basalt* was extruded into the Pasco Basin.
paleomagnetism - The fossil magnetism in rocks, used to determine the past configurations of the continents and to investigate the past shape and magnitude of the earth's magnetic field. The record of geomagnetic reversals preserved in volcanic and sedimentary rock sequences (magnetostratigraphy) provides a time-scale that is used as a geochronologic tool. Certain minerals in rocks lock-in a record of the direction and intensity of the magnetic field when they form. This record provides information on the past behavior of Earth's magnetic field and the past location of tectonic plates.
patterned ground - Well-defined; more or less symmetrical forms; such as circles; polygons; nets; steps; and stripes; that are characteristic of; but not necessarily confined to; surficial material subject to intense frost action; especially in polar; subpolar; and arctic regions. Patterned ground in the Pasco Basin; however; appears to be related to seismicity* that occurred during or soon after cataclysmic flooding.
pedogenic - Relating to the processes that produce soil.
pendant bar - A type of flood bar* that forms immediately downstream of an obstruction in the flow of the flood current.
Pleistocene Epoch - The period of geologic time between 10;000 and 2.5 million years before the present. The Pleistocene essentially spans the same period of time known as the Ice Age.
Pliocene Epoch - An epoch of the Tertiary period; after the Miocene and before the Pleistocene.
plunge pool - A deep pool or basin formed at the foot of a waterfall.
pluvial lake - A lake formed in the Pleistocene epoch* during a time of glacial advance; and now either extinct or existing as a remnant.
point bar - An arcuate (curved or bow-shaped) ridge of sand* and gravel* developed on the inside of a growing meander (loop) in the course of a stream.
radiometric - Refers to methods of age determination based on the nuclear decay of radioactive isotopes.
reverse grading - Refers to sedimentary* beds that show an increase in particle size upward within the bed; as opposed to normal grading which shows a decrease upward. Most flood rhythmites* display normal grading.
reverse or thrust fault - A fault; usually with a dip of >45 degrees; where the hanging wall has moved up relative to the footwall of the fault.
rhythmite - A graded sedimentary* layer; several inches to several feet thick; deposited under slackwater* conditions; especially in backflooded valleys during cataclysmic floods. Some believe that each rhythmite represents a separate cataclysmic flood from glacial Lake Missoula*.
Ringold formation - Sediments stratigraphically overlying Columbia River basalt* and underlying cataclysmic flood deposits in southeastern Washington. Mostly derived from ancient river and lake deposits that accumulated within the ancestral Columbia River basin between about 8.0 million and 3.4 million years ago.
rip-up clast - Sedimentary* material that has been eroded and transported only a short distance in a semi-consolidated (e.g.; frozen) state.
sand - Sedimentary* particles that are between 0.06 to 2.0 mm in diameter.
Sangamon Interglacial - The time period between glacial stages; roughly 130;000-80;000 years ago; when climatic conditions were similar to those of today.
sedimentary - Composed of sediment. One of the three principal rock types; along with igneous* and metamorphic*.
seismicity - Earth vibrations and shaking due to earthquake activity; as well as those artificially induced.
silt - Small; sedimentary* particles between 0.06 to 0.004 mm in diameter.
slackwater - Refers to areas with slower moving flood waters associated with cataclysmic flooding (i.e.; backflooded valleys and valley margins) where fine-grained sediment (mostly sand* and silt*) was deposited.
soft-sediment deformation - Deformation that occurs during or soon after sediment deposition while sediment is still partially or fully saturated with water. Examples of soft-sediment deformation include flame structures; load structures; and clastic dikes*.
soil horizon - A distinct interface (surface or thin layer) in a stratigraphic sequence.
subglacial - Formed or accumulated in or by the bottom parts of a glacier or ice sheet.
of or relating to the structure of the earth's crust and the large-scale processes that take place within it.
tephra - Airfall deposit from a volcanic eruption. Usually consists of distinctive; light-colored; well-sorted; gritty particles of ash.
venturi effect - The principle that fluid moving through a smaller area will move at a higher velocity than the same amount of water moving through a larger area. As an example; floodwater moving through a narrow opening such as Wallula Gap* was moving much faster; with significantly more erosive power; than the water above or below the gap
Wallula Gap - The narrow constriction; only a few miles wide; through which all floodwaters from glacial Lake Missoula* passed on their way to the Pacific Ocean. During the largest floods; the water within Wallula Gap was over 1;200 ft deep.
Wisconsinan - Pertaining to the classical fourth and last glacial stage of the Pleistocene Epoch* in North America; following the Sangamon interglacial* and preceding the Holocene Epoch*. The late Pleistocene Wisconsinan glacial stage occurred between about 80;000 and 15;000 years before the present.