a'a —a lava rock with a ropey, frothy surface texture formed as a cooling crust on a fluid lava flow. ablation —the removal of snow and ice by melting or evaporation, typically from a glacier or ice field. abrasion —the process of wearing down or rubbing away by means of friction, typically by wind-blown dust or sand. absolute dating —general term applied to a range of techniques that provide estimates of the age of objects, materials, or sites in real calendar years either directly or through a process of calibration with material of known age. Absolute dating methods include the study of the decay radioactive isotopes (such as C14, and uranium to lead, and potassium to argon) abyssal plain —an underwater plain on the deep ocean floor, usually found at depths between 3000 and 6000 meters. accretion —a process by which material is added to a tectonic plate or a landmass. This material may be sediment, volcanic arcs, seamounts or other igneous features, or blocks or pieces of continental crust split from other continental plates. active continental margin —a continental margin that is characterized by mountain-building activity including earthquakes, volcanic activity, and tectonic motion resulting from movement of tectonic plates. alluvial fan — An outspread, gently sloping mass of sediment deposited by a stream where it issues out of the mouth of a narrow canyon draining from and upland area. Viewed from above, an alluvial fan typically has the shape of an open fan with the apex being at the mouth of the canyon. Alluvial fans are common in arid to semi-arid regions, but can be covered with forests in the California Coast Ranges. Alluvial fans may merge together to form an apron-like slope along the base of a mountain front. alluvium — A general term for unconsolidated sediments deposited by flowing water on stream channel beds, flood plains, and alluvial fans. The term applies to stream deposits of recent times and it does not include subaqueous deposits, such as in lakes or undersea. amphibole —Any of a class of rock-forming silicate or aluminosilicate minerals typically occurring as fibrous or columnar crystals consisting of hydrated double silicate minerals, such as hornblende , containing various combinations of sodium, calcium, magnesium, iron, and aluminum. amphibolite —a dark rock with fibrous crystals of amphibole and related minerals (tremolite, actinolite, and hornblende), both intrusive igneous or metamorphic in origin. anaglyphic image —A type of photographic image or drawing that can create a three-dimensional view when viewed through colored filter glasses—red-and-cyan colored lenses are most common (standard). Anaglyphic images are created using two standard photographs taken in parallel position a short distance apart, then colors are subtracted from the two images (blue and green from the left image, and red from the right image) before the two images are merged into a reconstructed image (called an anaglyph). The red colored lens filters out green and blue from the anaglyphic image whereas the cyan colored lens filters out the red. With red-and-cyan 3D viewing glasses on, the brain reconstructs a 3D view from the original stereo pair of images used to make the anaglyphic image. Standard anaglyphic 3D glasses are worn with the red lens over the left eye. andesite —A fine-grained, brown or grayish volcanic rock that is intermediate in composition between rhyolite and basalt, dominantly composed of plagioclase feldspar. anthracite —a hard, metamorphic variety of coal, having a low volitile content. Typically burns very hot and clean relative to other varieties of coal. anticline —a fold in layers of rock where the concave side faces down, with strata sloping downward on both sides from a common crest. aphanitic texture —dense, homogeneous rock with constituents so fine grained that they cannot be seen by the naked eye. aquiclude —an impermeable body of rock or stratum of sediment, or an impermeable fault zone, that acts as a barrier to the flow of groundwater. aquifer —a porous and permeable rock or sediment layer, such as a sand or sandstone, containing groundwater that can be used to supply wells. aquitard —a zone or layer of low permeability adjacent to an aquifer; the permeability is so low it cannot transmit any useful amount of water. Aquitards act as confining layers to confined aquifers. Confined aquifers can be used as water storage. arete —a narrow, jagged mountain ridge that divides two cirques or glaciated valleys. argillite —a metamorphic rock, intermediate between shale and slate, that does not possess true slaty cleavage. arroyo —a watercourse (water-carved gully, channel) in an arid region. Arroyos are typically dry (ephemeral) but are prone to flash floods after rare seasonal thunderstorms. artesian well —a well drilled through impermeable strata to reach water in a confined aquifer capable of rising to the surface by internal hydrostatic pressure. ash fall —A cloud of volcanic tephra, mostly dust (silt-sized) grains, that blankets a region from a volcanic eruption. asteroid —any of the thousands of small irregularly shaped bodies of stone, metal, and ice that revolve about the sun. In our solar system, asteroids typically range in size from about one-mile (1.6 km) to about 480 miles (775 km) in diameter and mostly lie in in orbits between those of Mars and Jupiter, however many large objects have been observed passing through Earth's orbital path. Asteroid collisions with earth were frequent in Earth's early history, but are now extremely rare events. The extinction of the dinosaurs and many other species is mostly blamed on the environmental catastrophe created by an asteroid impact about 65 million years ago, defining the end of the Cretaceous Period (and Mesozoic Era). asthenosphere —a semifluid layer of the earth, between about 40 to 80 miles (100-200 km) below the outer rigid lithosphere (oceanic and continental crust) forming part of the mantle and thought to be able to flow vertically and horizontally, enabling sections of lithosphere to subside, rise, and undergo lateral movement associated with plate tectonics. atmosphere —The gaseous mass or envelope surrounding a celestial body (including the one surrounding the Earth), and retained by the celestial body's gravitational field. The Earth's atmosphere is subdivided into levels: the troposphere is the lowest portion (up to about 6-8 miles) where all weather takes place and contains about 80% of the air's mass and 99% of water vapor. The overlying stratosphere contains an abundance of ozone which absorbs ultraviolet radiation, protecting life on land and in the shallow ocean extends up to about 31 miles. The upper atmosphere extends upward to the transition into space above about 60 miles where the charged atomic particles of the solar wind begins to interact with atmospheric gases. atoll —A ring-shaped reef, island, or chain of islands formed of coral, typical on a foundation of an extinct volcano in the ocean. atomic structure —the arrangement of the parts of an atom, which consists of a massive, positively charged nucleus (composed of protons and neutrons) surrounded by a cloud of electrons arranged in structured orbital arrangements. aureole —a zone of altered rock around an igneous intrusion. Heat and escaping fluids from the intrusion metamorphose the surrounding rock and may be a location where unusual and/or valuable mineral deposits accumulate. avalanche —a mass of snow, ice, rocks, and debris falling rapidly down a mountainside. badlands —uncultivatible land with typically rugged relief, a heavily eroded appearance, and bares little or no vegetation. bajada —an alluvial plain along the base of a mountain front formed from the accumulation and coellescing of of alluvial fans. barrier island —a long and typically narrow island, running parallel to the mainland, composed of sandy sediments, built up by the action of waves and currents. Barrier islands serve to protect the mainland coast from erosion by surf and tidal surges. basalt — A dark-colored igneous rock, commonly extrusive (from volcanic eruptions) and composed primarily of the minerals of calcic plagioclase and pyroxene, and sometimes olivine. Basalt is the fine-grained equivalent of gabbro. base level —the lowest level to which a land surface can be reduced by the action of running water, typically equivalent to the lowest point a river or stream can reach entering the ocean or other large body of water. Base level of a stream entering the ocean will rise and fall with changes in sea level. batholith —a great mass of igneous rock, extending to great depths, formed from extensive magmatic intrusions over a long period of time and throughout a region, typically associated with volcanic arcs. bedrock —relatively "fresh" unaltered solid (consolidated) rock below the surface sediment cover or exposed in rocky outcrops. beheaded stream —Streams draining across an active strike-slip fault trace may be captured by an adjacent stream. With loss of its water supply or a source of sediments, the older channel will remain as a beheaded stream channel as fault motion continues. bioaccumulation —the buildup of organic remains, such as coral reefs, peat, algae, plankton, and shell or bone beds. biosphere —the regions of the surface and atmosphere of the Earth (or possibly other planets) occupied by living organisms. biotite —a common rock-forming mineral occurring in black, dark-brown, or dark -green sheets and flakes: an important constituent of igneous and metamorphic rocks; a mafic variety of mica. bioturbation —the stirring or mixing of sediment or soil by organisms, especially by burrowing, boring, crawling, feeding or other traces left by biological activity. bituminous coal —soft black coal with a high volatile content, and typically burns with a smoky yellow flame. black smoker —a geothermal vent on the seabed that ejects superheated water containing much suspended matter, typically black sulfide minerals that accumulate around the vent on the seafloor. bollide —a large meteor (or asteroid or comet) that explodes in the atmosphere. Bowen’s reaction series —observed order of formation of silicate minerals as they form in a cooling melt (magma) resulting in the orderly formation of high temperature to low temperature minerals (rocks)—felsic minerals (and rocks) melt at lower temperatures that mafic minerals (and rocks). This was demonstrated by the work of "19th century petrologist" Norman Bowen, who showed that as a silicate-rich melt cools, minerals that form at higher temperatures will crystallize first. As these minerals crystallize, the chemistry of the remaining melt will change as it cools, allowing different minerals to form as the melt proceeds cooling. High-temperature minerals like olivine and Ca-rich feldspar cool first, minerals like quartz, K-rich feldspar, and biotite crystallize last. Fluids, such as gases and water, are concentrated in the remnants of a melt. breccia —a rock consisting of angular rock fragments cemented together. calcite —a common rock-forming mineral consisting of calcium carbonate—CaCO 3 . Calcite can be white, colorless (transparent), or slightly colored, commonly yellow, by other inclusion of traces of other elements. Calcite is a major constituent of sedimentary rocks such as limestone, chalk, and travertine, and in the metamorphic rock form, marble. caldera —a large volcanic crater, typically one formed by a major eruption (explosion) or the inward collapse of a volcanic cone following an eruption. caliche —a hardened zone in soils and surficial deposits found in semiarid regions where of calcium carbonate and possibly other carbonates, clay minerals, or crystalline salts such as sodium chloride or sodium nitrate impregnated the pore spaces in the sediment or soil. calving —blocks of ice falling off the face of a parent glacier, ice shelf, or iceberg. capillary fringe — a subsurface layer above the water table in which groundwater seeps up from a water table by capillary action to fill pores. catastrophism —The doctrine that major changes in the earth's crust result from catastrophes rather than evolutionary processes. cavern —an underground passage formed by dissolution of rock (typically limestone) by flowing groundwater. "Cave" is often used as a substitute for the more correct term "cavern." cementation —processes that harden sediments through the precipitation of minerals in pore spaces between grains of rock and mineral fragments, binding them together. Cenozoic —The era of time spanning about 65 million years ago to the present. The term applies to rocks that formed or accumulated in that time period. The Cenozoic Era is subdivided into the Tertiary and Quaternary periods. chemical weathering —the breakdown (decomposition or decay) of rock by chemical mechanisms, the most important means being carbonation, hydration, hydrolysis, oxidation, and ion exchange in solution. chert — a hard, dense sedimentary rock, consisting chiefly of interlocking microscopic crystals of quartz and may contain opal. It has a conchoidal fracture and may occur in a variety of colors. chlorite —a dark green mineral consisting of a basic hydrated aluminosilicate of magnesium and iron, often formed by metamorphic alteration (low grade or retrograde greenschist metamorphic facies). cirque —a bowl-shaped, steep sided hollow at the head of a valley or on a mountainside, formed by glacial erosion. clastic —sediments or sedimentary rocks composed of fragments derived from older rocks; examples sandstone, conglomerate. clay minerals —Any of various hydrated aluminum silicates that have a fine crystalline structure and are components of clay (sediment). cleavage —the tendency of a crystallized substance to split along definite crystalline planes, yielding smooth surfaces. Coast Range Ophiolite —California geologic formation name; an assemblage of mafic and ultramafic igneous rocks associated with oceanic crust. In California, the “Coast Range Ophiolite” is of Jurassic to possibly Cretaceous age and whose origin is associated with the upper mantle and the lower oceanic crust of the ancient Farallon Plate. The Farallon Plate predates the development of the San Andreas Fault system, and rocks of the Farallon Plate were either subducted or partially accreted (merged) into the crust that now makes up the Coast Ranges. The Coast Range Ophiolite is associated with serpentinite terranes throughout much of coastal central and northern California. The modern Juan de Fuca Plate offshore of the Cascades volcanic range in Oregon and Washington is a remnant of what was once the greater Farallon Plate. col —a saddle in a glacially carved mountain ridge (a gap in an arete). colluvium —A general term applied to loose and incoherent surficial deposits, usually at the base of a slope and brought their chiefly by gravity. compaction —the process of gravitation consolidation of sediments, decreasing porosity and increasing hardness. condensation —the conversion of atmospheric water vapor into liquid water or ice (causing precipition). conglomerate —A coarse-grained sedimentary rock composed of rounded to sub-angular fragments (larger than 2 mm in diameter) set in a fine-grained matrix of sand or silt, and commonly cemented by calcium carbonate, iron oxide, silica, or hardened clay; the consolidated equivalent to gravel. continental crust —the relatively thick part of the earth's crust that forms the large landmasses. It is generally older and more complex than the oceanic crust, and dominantly composed of igneous and metamorphic of granitic or more felsic composition. continental drift— theory that continents were once assembled (noted from early maps by Abraham Ortelius in 1596). Promoted as a plausible theory by Alfred Wegener, 1912), but criticized for lack of mechanism. Plate Tectonic Theory evolved in the 1960 after global observation data first was assembled. continental rise —a wide, gentle incline from a deep ocean plain (abyssal plain) to a continental slope. A continental rise consists mainly of silts, muds, and sand, deposited by turbidity flows, and can extend for several hundreds of miles away from continental margins. Although it usually has a smooth surface, it is sometimes crosscut by submarine canyons extending seaward of continental slope regions. continental shelf —a submerged nearshore border of a continent that slopes gradually and extends to a point of steeper descent to the ocean bottom. During the peak of the last ice age, the world's continental shelves were mostly exposed coastal plain environments. continental shield —a large regions of igneous and high-grade metamorphic rock of Precambrian-age exposed in the tectonically stable core of continents; an example is the Canadian Shield in east central Canada and the Lake Superior region of the United States. continental slope —the slope between the outer edge of the continental shelf and the deep ocean floor. The continental slope is cut by submarine canyons in many locations. convergent boundary —when continents collide... mountains belts form - examples include the Himalayas, Alps, and ancient Appalachian Mountains when the ancient continent of Pangaea formed. When continents collide with ocean crust... subduction zones with deep ocean trenches and volcanic arcs form - examples include the Andes Mountains, Aleutian Islands, Japan, Philippines, Indonesia, the ancient Sierra Nevada and modern Cascades Range. coquina —a soft type of limestone composed almost entirely of compacted and cemented shell fragments, commonly found on upper beach ares in warm, humid climates. core —based on geophysical studies, the innermost part of the earth is believed to consist of a 758 mile thick magnetic metallic core overlain by a 1400 mile thick zone of molten material. This is overlain by the Earth's mantle. crater —a large bowl-shaped vent or collapsed top of a volcano created by explosive eruptions. Also a large bowl-shaped hole created by an meteor or asteroid impact and explosion. craton —the part of a continent that is stable and forms the central mass of the continent. The craton region of North America includes the region between the Rocky Mountains (to the west) and the Appalachian Mountains (to the east) and including the Canadian Shield. creep —in earthquake terminology, creep is the slow, more or less continuous movement occurring on faults due to ongoing tectonic deformation. In landslide terminology, creep is slow, more or less continuous downslope movement of surface materials (mineral, rock, and soil particles) under gravitational stresses. Cretaceous —the final period of the Mesozoic Era (after the Jurassic Period and before the Tertiary Period of the Cenozoic Era). The Cretaceous Period began about 144 million years ago and ended about 65 million years ago. crust — the outermost solid shell of a rocky planet or moon, which is chemically distinct from the underlying mantle. crystallization —the formation and growth of mineral crystals from the cooling of molten material. dacite —an extrusive igneous (volcanic) rock with an aphanitic to porphyritic texture and is intermediate in composition between andesite and rhyolite. Darcy's Law —the law that the rate at which a fluid flows through a permeable substance per unit area is equal to the permeability, which is a property only of the substance through which the fluid is flowing, times the pressure drop per unit length of flow, divided by the viscosity of the fluid. debris flood — typically disastrous flood, intermediate between the turbid flood of a mountain stream and a debris flow, ranging in sediment load between 40 to 70 percent (the rest is water and trapped gasses). debris flow — A moving mass of rock fragments, soil, and mud in which more than half of the particles being larger than sand size (otherwise it would be a mudflow) and with 70 to 90 per