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A partial glossary of terms, words, acronyms, abbreviations, and geojargon you might encounter in the BGC website. This is an ongoing creation, last updated on March 30, 2014.
BGC. Busch Geotechnical Consultants. The acronym for this company, originally founded in May, 1985, as Busch Geologic Consultants, but now also known in the short-hand of the new millennium as Busch Geotechnical or Busch Geotech. We are a firm composed entirely of geologists and engineering geologists.
Bedrock. Bedrock is the "basement rock" beneath the rock formations or soil horizons in an area of interest. There can be more than one type of bedrock, or "country rock," as some geologists call it, in an area. The "geophysical bedrock" is the deepest, densest, or oldest bedrock at a location (or all three, in some cases). In coastal California the geophysical bedrock typically is a ~165,000,000-year-old (+/-) lithology (rock type) of the Franciscan Complex. Inland it might be much, much older rocks. For example, in the Grand Canyon bedrock is the ~1.7 billion-year-old Vishnu Schist (and the intrusive Zoraster Granite). In some places in the canyon the next oldest overlying rock is the ~550 million-year-old Tapeats Sandstone (so there is a ~1.2 billion-year-old hiatus in the record. (In coastal Oregon, coeval, Franciscan-equivalent terranes are the Dothan Formation, Otter Point Formation, and others.
Bioclastic Debris. A clast of biological origin, for example, bivalve (clam) or gastropod (snail) shell fragments, pieces of barnacle scutes, or pieces of coral or calcareous algae. Contrast with Clastic Debris. See photographs in the Sand Collection page for images of bioclastic debris.
Blue Goo. A lay person's word for the sticky, plastic, bluish-gray gravelly clay weathered from pervasively sheared deposits of the Coast Ranges in California (primarily) and Oregon. In California, mudstones of the Jura-Cretaceous (to Eocene) Franciscan Complex form blue goo. In Oregon, mudstones of the coeval (same age) Dothan Formation form the stuff. Commonly seen in failing roadcuts along US 101. (Thanks to Christine Hills for the inquiry that prompted this definition. You too can ask a question!)
Cape Sebastian Formation. Cape Sebastian is the first headland south of Gold Beach, OR. Access it via Highway 101 and a well-maintained State Park road to the top, then hike down to the shoreline cliffs from the parking lot. Or, park on a pull-off along US 101 south of the Cape, then hike north along the shore. If you choose this way, check the tide table! The shoreline of the Cape features incredible differential weathering of the Cretaceous formation (see Photo Galleries, Rocks). The formation is a transgressive sequence (q.v.) of rocks. Shoreline exposures of conglomerates and gravelly sands are on the northern end of the Cape, differentially weathered littoral marine (midwater) sands are best exposed on the west side of the headland, and the south side sea cliffs expose steeply dipping deep-water turbidites (interbedded siltstones and argillites).
CIP. Cast-in-place, as in CIP reinforced concrete pier.
Clast. A piece of rock.
Clastic Debris. A group of grains and/or clasts of terriginous (land-originated) sediment, for example, group of mineral grains, lithic (rock) grains, sand or silt grains, rocks, etc.
Coeval. Of the same age.
Coralgal Sand. A bioclastic sand composed primarily of fragments of species of coral and calcareous algae. The sands can range from fine and well sorted to well-graded (all sizes of sand and larger clasts). Coralgal sands are common in subtropical and tropical regions.
CSZ (or Csz). The Cascadia subduction zone, the interface between the subducting (down-going) oceanic plates offshore and the over-riding North America plate, which extends from about Cape Mendocino in Humboldt County, CA, to British Columbia. These two plates lock together but episodically slip causing great earthquakes--magnitude 8 to 9+ earthquakes--off the Pacific Northwest coast. The great 1960 Chilean earthquake, the 1964 Alaska earthquake, the 2004 Andaman Sea earthquake, and the 2011 Japan earthquake were all subduction zone earthquakes. The last Csz event occured on January 26, 1700. The probability of the next 8+ one (on the southern segment, which extends from Cape Blanco, OR, south to Cape Mendocino, CA, currently is cited by USGS geologists as 37% in the next 50 years. The probability of a 9.0 or greater magnitude quake is cited at 10% within the next 50 yrs.
Debris Slide. In lay-language, a "mudslide." A debris slide is a type of mass movement of soil and rock that often initiates on a steep slope (often 65% and steeper) during or following a prolonged or intense rain (5" in 24 hours is a critical, landslide-triggering volume for many steep slopes). The debris slides, flows, or torrents downslope onto flatter ground or until the debris is completely spread out. Debris slides occur rapidly when increased water pressure in the pores of the hillslope soils causes saturated soils to suddenly decouple from the underlying soils and slide (or flow or torrent) downslope carrying trees, brush, and human improvements. The slide changes character as it incorporates more water: a debris slide can become a debris flow and then a debris torrent. The latter is essentially fast-flowing muddy water.
Earthflow. A plastic (versus brittle...melting butter vs breaking glass) type of deformation of soil in which the failing soil / broken rock materials typically tend to creep or otherwise move slowly downslope en mass, often above one or more slip planes or zones of movement that roughly parallel the slope of the ground surface. The type of movement in an earthflow is primarilyn translational (mostly lateral). Often the upslope (head) region of an earthflow begins as a rotational failure loosely called a "slump," hence the geojargon term "slump-earthflow" or "SEF" terrain. Common landforms in SEF terrain include hummocky (irregularly, mounded, bumpy) ground, supporting leaning conifers, indeterminate drainages (interupted, pinched off, and strangely short drainage paths such as swales and gullies), steps and backtilted benches, and others. SEF terrain is common in structurally weak bedrock such as pervasively shearted mudstone, argillite, silttone, and sandstone, particularly when it is on steep, wet, or surcharged (loaded) slopes, slopes undercut by an ocean river, or excavation, or slopes with several of these adverse factors.
Erosion Rate. The rate, in mm, cm, m, in, or ft/yr or other time increment, that land wastes away. Coastlines erode at highly variable rates that are a function of rock type, bluff height, bluff aspect, seasonal wave conditions, sediment availability, and earthquake frequency and magnitude. Mountainsides erode in response to heavy rains, freeze-thaw cycles, burrowing organisms, wind, seismic events, and other physical and biological factors.
Fill. Any material removed from its original location and brought to another location, or modified from its original state and reused on the same site, to support a structure, road, yard, whatever. An imported fill is a material brought to the job site from offsite. Typical examples include "river run" (silty sandy gravel to gravelly sand) and "crushed aggregate base" (crushed river run or crushed rock, generally smaller than 3/4" in maximum clast size.
Formation. A geologic unit of rocks that has been formally named. It is a mappable unit. In coastal California the common bedrock formation is the Franciscan Complex. In coastal Oregon, the nearly time-equivalent (coeval) units are the Dothan Formation and the Otter Point Formation. These formations are the "geophysical bedrock," or the deepest bedrock.
Geodetic Survey. A type of land survey done using the finest surveying equipment available (that with the greatest precision and repeatability), whose purpose is to record changes in elevation (or location) of the land. On-going geodetic surveys in the Pacific Northwest have discovered that the coastline from about Crescent City, CA, to Port Orford, OR (and beyond) is rising faster than GSL rise, so there is net uplift. Other areas are holding their own or subsiding, and some areas, for example, in the Puegot Sound region, are compressing laterally. There, mountain peaks are becoming closer together as North America is compressed by the down-going oceanic Juan de Fuca plate!
Geojargon. Geologist's jargon, e.g., SEF terrain (q.v.), transportational midslope, stress relief fracture, TOB (top-of-bluff), and countless more.
Geologic Hazard. A threatening event such as a landslide, earthquake, fill failure, soil settlement, volcanic eruption, tsunami, marine erosion event, and so on. Contrast with Geologic Risk. A damage hazard can result from a geologic hazard. Examples include ground cracking, tilting, settling, tree fall, broken utility lines, fire, etc. That is, one geologic hazard, e.g., a landslide, can pose different types of damage hazards, each with its own probability of occurence or associated level of risk.
Geologic Survey. A layperson's term for a wide variety of geologic services. When a client asks for a "geologic survey," a BGC geologist has to determine, by asking questions, precisely what the client's goal is and what type of geologic investigation is necessary to achieve that goal.
Geomorphic Mapping. Making a plan view map, to-scale if possible, of the various landforms that make up a property or terrain of interest. Example landforms include ridges, fault scarps, gullies, swales, creep slopes, landslide head scarps, and countless others.
Great Earthquake. An earthquake with a magnitude of 8.0 Mw or greater. Cf. Strong Earthquake.
Hiatus. A gap or missing section in a rock record, usually caused by the erosion of the missing member or formation. The angular unconformity (the Great Unconformity) in the Grand Canyon, which is between the ~1.7 billion-year-old Vishnu Schist and the ~550 million-year-old Tapeats Sandstone (in places) represents a hiatus (lost rock record) of ~1.2 billion years.
High-Energy Beach. A beach characterized by a moderate to steep face, well graded (many sizes of) sands, coarse sands, pebbly sands, or gravels, cobbles, and/or boulders. In the PNW, high energy beaches often face SW, W, or NW and are not protected by offshore rocks, headlands, or low-gradient offshore slopes. Because of the steep face, arriving swell typically peaks and breaks only a few tens of feet from the base of the swash zone, causing surging waves to rush up high onto the beach. Such beaches often have dangerous, strong rip tides. Examples include the Great Beach at Point Reyes National Seashore, nearly all of the Lost Coast beaches between Point Delgada and the Mouth of the Mattole River (Humboldt Co., CA), Agate Beach at Big Lagoon (Humboldt Co.), and Freshwater Lagoon Beach (Humboldt Co.). Cf. Low-energy Beach.
Inboard (adj.) / Inslope (v): The inboard side of a road is the upslope or uphill side. The outboard side is the outside or downhill side. To inslope a road is to grade it so that water falling on the road runs toward the cutbank, which usually has an inboard ditch below it. The PROBLEM with insloped roads is that when a cutbank failure occurs, it blocks the ditch and spills water across the road, sometimes causing significant erosion on the slope below the road.
Low-Energy Beach. A strand of shoreline sand most commonly characterized by a negligibly to gently sloping beach face, fine to very fine sand, offshore sands, and low-energy (small amplitude) waves. Such beaches are protected or semi-protected from large waves by the gentle offshore slope, which causes the waves to break out away from the shoreline and roll in, loosing energy. Some Northern California examples include Moonstone Beach (south of Trinidad, CA) and Crescent City Beach. cf High-Energy Beach.
Melange. Melange is a mixture of rock types formed when deep sea sediments and oceanic volcanic rocks such as pillow basalt are subducted down into the lower crust. The sediments turn to rock (are lithified) but are sheared, faulted, fractured, and folded in the process, and are mixed together. In some areas, melange contains mappable bodies of sedimentary rocks that retain much of their primary sedimentary structure, but in other areas it is more typically a gravelly mudstone. See Blue Goo.
Provisionally Stable. In BGC's in-house stability classication, a Provisionally Stable slope is a "marginally stable" slope, one that is "stable" when investigated and classified, but one recognized as being susceptive to a slope failure if extrinsic forces such as prolonged rain, an earthquake, or earthworks
RDR. A Busch Geotechnical Consultants' acronym for Reality Disclosure Report, shortened down from GRDR (Geotechnical RDR). We write RDRs to help sellers of real estate disclose geologic hazards and risks and to help potential buyers understand property conditions and risks. Banks, credit unions, and private lenders also have found them useful.
Risk. The qualitative estimate or mathematical probability that a hazard will occur. See Hazard. In BGC's terminology, a level of risk is associated with a hazard. Some of our competitors use "hazard" and "risk" interchangeably, but they are NOT the same thing.
Road Prism. The road prism is the section of a road from the top of the cutbank or cutslope to the toe or base of the fill slope. That said, some geologists use "road prism" to mean only the fill prism of the road.
SEF. Geojargon for "Slump-earthflow." A SEF is a type of landslide in which rotational failures (slumps) occur in the head region of a slide and then the failed masses creep rapidly downslope at rates of mm to ft/day. The moving mass is translational in nature. Generally the slide plane or failure zone or group of slide planes roughly parallels the slope of the ground surface. A "surge" occurs when the movement rate rises rapidly, sometimes to catastrophic levels.
Settlement. The predominately vertical lowering of elevation of a ground surface (often one composed of a poorly compacted fill) due to either the localized consolidation (compaction) of soils in the subsurface or to the widespread overall lowering of the land surface due to an especially strong earthquake. This latter, rare type of settlement is called coseismic Subsidence (= settlement due to an earthquake).
SFR. Single-family residence.
Slope Inclinometer. An inclinometer is a delicate (and expensive) sensor or probe that is used in a borehole to determine if the ground is moving and, if so, in which way(s). The probe is lowered into a specially grooved casing that was set into a borehole, then withdrawn incrementally. It feeds electronic data on the verticality of the borehole to a recorder. By comparing an initial data set with subsequent data sets a geologist can determine if the ground is moving, how deep it is moving, in which direction, and how fast.
Slope Profile / Geologic Cross Section. A profile is a side or "along the slope" view of a landform, for example, a coastal bluff. A profile shows the lengths of slope segments and their steepness in percent or degrees. Once labeled with information such as top-of-bluff, headscarp, tension crack, leaning trees, spring, etc., a profile becomes a "single line" geologic picture. By adding subsurface information to the profile, for example, the thickness of marine terrace sediments or other soil masses, or the location of a bare rock outcrop, the profile becomes a geologic cross-section. Think of a cross section this way: you cut an apple in half, starting at the stem, then you throw away (or eat) the half nearest you. The view of the inside of the apple...skin, meat, seeds...is a cross section.
Slope Stability Analysis. A qualitative (experience or "eyes only") assessment or a mathematical ("Factor of Safety) assessment of the probability of failure of a specific slope of interest.
Slope Stability Assessment. The classification of the relative stability of an area of interest using qualitative methods (experience or "eyes only" means) or mathematical computations ("Factor-of-Safety Analysis). BGC uses a six-fold qualitative classification: Very Stable, Stable, Moderately Stable, Provisionally Stable, Unstable, and Very Unstable. Each stability class has diagnostic features recognizeable in the field.
SMARA. Surface Mining and Reclamation Act.
Soil Log. A written record of the earth materials encountered during a subsurface exploration, be it by augur, drill rig, or backhoe. Also called a Borehole Log and Test Pit Log. Other types of "logs" exist as well.
Soil Index Test. A soil has physical properties such as color, texture, density, water content, compressibility, shear strength, plasticity, mineral and/or rock content, and others. The first types of tests done in a soil lab to characterize a soil generally are the fastest, easiest, least expensive ones. They yield "index parameters" such as texture (the size and frequency distribution of the grains), field density (the unit density at the field moisture), dry density (the unit density of a dried sample), and moisture content (the weight percent of water in a field sample).
Strong Earthquake. An earthquake that measures between about magnitude 5 and 7.9 on the Richter scale, the earthquake strength scale used by geologists. Cf. Great Earthquake.
Tectonic. Having to do with mountain building, regional subsidence, faulting, or plate interactions. A "tectonic event" could be the uplift of a mountain range, the shifting of a continent, the sinking of a landmass, and similar earth-scale processes.
Tiltmeter. A tiltmeter baseplate is a butter-plate-sized bronze plate with four nipples or pegs on it, one at each of the cardinal azimuths (N,E,S,W). After we epoxy the baseplate onto a rock, cement surface, or metal rod-like in-ground assembly, a tiltmeter (the sensor) reads the degrees off horizontal of the baseplate and a datamate recorder keeps the data. By comparing an initial reading to subsequent readings, a geologist can determine if the ground is tilting, which way, how much, and at what rate. Tiltmeters are a comparatively low-cost method of determining if the ground or a structure (such as a retaining wall) is moving and if the movement is potentially significant. See photographs in Current Work, 2013.
Transgressive Sequence. Considered from the bottom beds up (moving higher in the sequence), a transgressive sequence is a collection of geologic units or rock types that originated in progressively deeper water. It forms as the ocean rises (or the lands sinks) and water inundates the landsurface. The resultant sedimentary deposit reflects a deeper and deeper depositionary environment. An example of a transgressive sequence of rocks is a conglomerate (abrasion platform and beach deposit) covered by a littoral marine sandstone (nearshore deposit) underlying a siltstone or turbidite sequence (deep water deposits). The Cape Sebastian Sandstone (q.v.) is a transgressive sequence of Cretaceous rocks.
Turbidite. A turbidite is a deep-water sedimentary deposit consisting of alternating layers of mud and sand (if still a soft sediment) or mudstone and siltstone and/or sandstone (if a rock). A turbidite forms as fine-grained clastics settle out of the water column onto the continental slope or abyssal plain. When an underwater landslide--often triggered by a large magnitude earthquake--jars loose unconsolidated sediments, they flow downslope as a roiling cloud of suspended grains and particles called a turbidity current. The densest grains settle out first, so a one-event "package" of sediments typically consists of fining-upward sands beneath silts beneath clays (sandstone under siltstone under mudstone). Mud deposit will continue until the next upslope or up-canyon event brings another turbidity current down.
USCS. Unified Soil Classification System. This is the soil classification used by engineers and engineering geologists. Research geologists and soil scientists use other classifications, e.g., the USDA or Wendtworth-Udden (q.v.) There are only three (3) sizes of sand in the USCS classification: coarse, medium, and fine.
USDA. U.S. Department of Agriculture (soil classification). Soil scientists, environmental scientists, and consultants doing septic suitability studies commonly use the USDA soil classification. In contrast to the USCS, it has five (5) sand sizes: very coarse, coarse, medium, fine, and very fine.
Uplift. The rising of a landmass (including submarine ones) in response to a tectonic force such as subduction or other types of plate collisions. Cf. Coseismic subsidence.
Water of Hydration. Water contained within the structure of a mineral, for example, water molecules between sheets of clay in clay minerals. Water of hydration appears in the chemical formula for the mineral as H2O. When drying soils containing clay to determine the percent-water in the sample, the lab technician must maintain the oven temperature below 105 degrees Celsius to avoid removing the water of hydration and thus producing incorrect percent-moisture data.