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Typical rock mass containing numerous discontinuities. The person in picture is conducting a scanline survey, where a tape is placed across the rock and detailed information is gathered on the fractures that intersect the scanline.

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from article Rock mechanics

(a) Uniaxial compression test, where an axial stress is applied to a core sample of rock and increased until failure. (b) Triaxial compression test, where a constant confining stress is first applied, then the axial stress is increased until failure.

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from article Rock mechanics

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from article Rock mechanics

(a) Example of the failure zone around an underground excavation (×, shear failure; o, tensile failure), calculated using the Rocscience Phase2 computer program. (b) Example of a shallow underground excavation where the failure mode is either…

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from article Rock mechanics

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from article Flax

Flax plants (Linum usitatissimum) in bloom. (Photo by Howard F. Schwartz, Colorado State University)

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from article Flax

Flaxseeds. (Photo by Jose Hernandez, U.S. Department of Agriculture–Natural Resources Conservation Service PLANTS Database)

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from article Flax

Yellow wilted leaves of flax plants infected by Fusarium oxysporum. (Photo by J. A. Hoes, Oilseed Diseases Image Collection, Western Committee on Plant Disease, Winnipeg, Manitoba, Canada)

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from article Flax

Blighted and moldy flaxseeds. (Photo by J. A. Hoes, Oilseed Diseases Image Collection, Western Committee on Plant Disease, Winnipeg, Manitoba, Canada)

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from article Peppermint

Peppermint (Mentha piperita). (Photo by Michael Thompson, Agricultural Research Service, U.S. Department of Agriculture)

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from article Citron

Citron (Citrus medica), including cross sections of the fruit. (Photo courtesy of California Citrus Clonal Protection Program)

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from article Cabbage

Cabbage (Brassica oleracea var. capitata). (Joseph Harris Co., Inc., Rochester, New York)

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from article Atmospheric acoustics

Frequency dependence of attenuation coefficient in units of decibels per 100 m (dB/328 ft), temperature of 20°C (68°F), and a relative humidity of 70%. Total attenuation from air absorption and contributions from classical absorption (that due to…

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from article Atmospheric acoustics

Diagram of reflection of sound from a flat ground surface with impedance Z, showing direct (R1) and reflected (R2) paths from source to receiver, source height hs, microphone height h, distance of propagation d, and angle of incidence or grazing…

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from article Atmospheric acoustics

Relative sound pressure levels (SPL) for propagation from a source over mown grass for source height of 1.8 m (6 ft), microphone height of 1.5 m (5 ft), and distances of propagation indicated.

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from article Atmospheric acoustics

Curved ray paths. (a) Refraction downward, during temperature inversion or downwind propagation. (b) Refraction upward, during temperature lapse or upwind propagation.

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from article Atmospheric acoustics

Representative long-range ray paths of sound radiating from a source in the atmosphere and traveling from west to east in Northern Hemisphere in winter. 1 km = 0.6 mi. (After T. F. Malone, ed., Compendium of Meteorology, American Meteorological…

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from article Atmospheric acoustics

Contour plot of sound levels in the presence of upward refraction in a turbulent atmosphere. The source is very close to the ground at zero range. The white areas are regions of higher sound levels.

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from article Atmospheric acoustics

Facsimile record of acoustic echo sounding of atmosphere at the South Pole, February 9, 1975. 300 m = 984 ft, 600 m = 1969 ft. Dark regions above 300 m altitude correspond to temperature inhomogeneities associated with the passage of convective…

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from article Surface waves

Definition sketch for an oscillatory wave.

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from article Surface waves

Fluid particle orbital motions in deep-and shallow-water oscillatory waves. SWL = still-water level.

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from article Surface waves

Definition sketch for a solitary wave. SWL = still-water level.

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from article Surface waves

Definition sketch for a surge wave.

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from article Layered intrusion

Sequence of crystallization from basaltic magma. (a) Hypothetical phase diagram showing the derivation of the sequence olivine cumulate, orthopyroxene-olivine cumulate, orthopyroxene cumulate, as observed in cyclic units near the base of many…

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from article Layered intrusion

A sequence of layers of near-constant thickness and aspect that show a rather abrupt transition from a base rich in pyroxene (pyroxene-plagioclase cumulate) to a top composed nearly entirely of plagioclase (plagioclase cumulate). Ice axe is…

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from article Layered intrusion

Photomicrograph of an olivine cumulate from the LaPerouse gabbro. Early-crystallized olivine grains (ol; now fractured and incipiently altered) are enclosed in interstitial plagioclase (pl) and orthopyroxene (px). Mineral proportions suggest that…

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from article Layered intrusion

Repetitive darker layers of pyroxene cumulates within a thick sequence of relatively monotonous orthopyroxene-plagioclase cumulates, Dufek intrusion, Antarctica. Total thickness of cumulates shown is 1750 ft (530 m). (Art Ford, U.S. Geological…

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from article Weather forecasting and prediction

Correlation coefficients between 3-day, 4-day, and 5-day forecasts of sea-level pressure made by the National Meteorological Center and observed sea-level pressure. Domain of verification is North America and adjacent ocean areas. (Courtesy Wayman…

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from article Weather forecasting and prediction

The quality of weather forecasts, defined as the product of the accuracy and detail achievable, depicted schematically as a function of lead time for two different forecasting methods. Traditional forecasts based on numerical weather prediction deal…

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from article Weather forecasting and prediction

Daily average temperature at Des Moines, Iowa. The thinnest curve indicates daily average temperature for January 1–December 31, 1994. The thickest curve indicates the 90-day running mean. The remaining curve indicates the 30-year average of daily…

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from article Glacial geology and landforms

Worldwide glaciation: (a) present distribution and (b) 18,000 years ago at the maximum of the Late Wisconsinan. (Modified from T. L. McKnight and D. Hess, Physical Geography, 6th ed., 2000)

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from article Glacial geology and landforms

Striations and chattermarks on bedrock in front of Omsbreen, Norway, ice moving from right to left. People are shown for scale.

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from article Glacial geology and landforms

Erratic boulder, approximately 3 m (10 ft) high, sitting on the side of a field in southern Ontario, Canada.

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from article Glacial geology and landforms

Large pothole (glacial P-form), Finland. (Geological Survey of Finland).

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from article Glacial geology and landforms

Roche moutonée, approximately 25 m (80 ft) in length in front of the Nigardsbreen Glacier, Norway, with ice moving from right to left.

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from article Glacial geology and landforms

Fluted and streamlined bedrock forms: (a) small-scale flutes, Wilton, Ontario; (b) P-forms in bedrock, Espanola, Ontario; (c) subglacial meltwater erosion marks; and (d) P-forms, Espanola, Ontario (scale card is 8.5 cm long).

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from article Glacial geology and landforms

U-shaped valley, Muick, Scotland.

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from article Glacial geology and landforms

Erosional landscape system for alpine glaciation. (a) Region during period of maximum glaciation. (b) Glaciated topography. (Modified from E. J. Tarbuck and F. K. Lutgens, 2003)

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from article Glacial geology and landforms

Rogen moraine near Uthusslön, Sweden. (Courtesy of Jan Lunqvist)

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from article Glacial geology and landforms

Drumlin S. (a) General model, showing the variability of the internal composition. (b) Green Bay Lobe, Wisconsin. Ice direction from the upper right to lower left. (Courtesy of D. Setz)

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from article Glacial geology and landforms

Fluted moraine, Storbreen Glacier, Norway. Note boulder at he head of the flute; ice direction bottom right to middle left.

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from article Glacial geology and landforms

End moraine. (a) Findelen Glacier, Switzerland (courtesy of J. Matthews). (b) Sequence of retread of end moraines from Storbreen Glacier, Norway.

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from article Glacial geology and landforms

Esker ridge, Bylot Island, Canada. (Courtesy of C. Zdanowicz)

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from article Glacial geology and landforms

Models of (a) land-based glacial depositional system and (b) depositional system of an ice mass with a marine moraine.

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from article Glacial geology and landforms

Late Wisconsinan end moraines of the Green Bay Lobe, Lake Michigan Lobe, and Huron-Erie Lobe. (Modified from J. C. Frye and H. B. Willman, 1973)

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from article Playa

Dry lakebed, or playa, with the Warner Mountain Range, northeastern California, in the distance. (USGS).

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from article Plains

Ideal stages in the progressive development of a stream-eroded landscape. (a) Youth. (b) Maturity. (c) Old age. (After G. T. Trewartha, A. H. Robinson, and E. H. Hammond, Elements of Geography, 5th ed., McGraw-Hill, 1967)

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from article Plains

Surface form and structure of cuestas. Dissected form at right is more typical, especially in humid regions. (After G. T. Trewartha, A. H. Robinson, and E. H. Hammond, Elements of Geography, 5th ed., McGraw-Hill, 1967)

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from article Plains

Types of floodplains. (a) With braided channel. (b) With sinuous channel but too narrow for free meandering. (c) With freely meandering channel. (After G. T. Trewartha, A. H. Robinson, and E. H. Hammond, Elements of Geography, 5th ed., McGraw-Hill,…

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from article Plains

Salt marsh, swamp, and natural levee lands in the Mississippi River delta. 1 mi = 1. 6 km. (After G. T. Trewartha, A. H. Robinson, and E. H. Hammond, Elements of Geography, 5th ed., McGraw-Hill, 1967)

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from article Plains

Alluvial fans in the Mojave Desert, southeastern California. (J. L. Balsley, U.S. Geological Survey)

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from article Plains

Extent of former continental glaciers in North America and Eurasia. (After G. T. Trewartha, A. H. Robinson, and E. H. Hammond, Elements of Geography, 5th ed., McGraw-Hill, 1967)

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from article Plains

Diagram of the drainage pattern of a glaciated plain in eastern Wisconsin. 1 mi = 1.6 km. (After G. T. Trewartha, A. H. Robinson, and E. H. Hammond, Elements of Geography, 5th ed., McGraw-Hill, 1967)

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from article Plains

Plains of former glacial lakes in North America. (After G. T. Trewartha, A. H. Robinson, and E. H. Hammond, Elements of Geography, 5th ed., McGraw-Hill, 1967)

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from article Plains

View of an ideal tableland: Canyon de Chelly National Monument, northeastern Arizona. (Spence Air Photos)

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from article Plains

Death Valley, California, a basin of interior drainage in the Basin-and-Range province. (Courtesy of John S. Shelton)

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from article Aragonite

Aragonite. (a) Pseudohexagonally twinned specimen from Girgenti, Sicily (American Museum of Natural History specimens). (b) Arrangement of pseudohexagon twins (after C. Klein, Dana's Manual of Mineralogy, 21st ed., John Wiley and Sons, 1993).

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from article Lespedeza

Sericea lespedeza (Lespedeza cuneata). (Photo by Chuck Bargeron, University of Georgia; Bugwood.org)

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from article Atmosphere

Layers of the atmosphere. (Credit: NOAA)

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from article Atmosphere

Annually and globally averaged radiation energy budget of the Earth's atmosphere expressed as percentages of the total incoming solar radiation. (Credit: NOAA/National Weather Service)

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from article Atmosphere

Temperature of the atmosphere plotted as a function of height and showing the various layers. (Credit: NOAA)

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from article Sisal

Sisal (Agave sisalana). (Photo courtesy of Peter Lapshin)

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from article Wool

Sheep at a research facility near Dubois, Idaho. (Photo courtesy of the Agricultural Research Service, U.S. Department of Agriculture)

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from article Wool

Longitudinal section of a completely developed nonmedullated wool follicle, including sebaceous and sweat glands.

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from article Wool

Cuticle, cortex, and medulla of a wool fiber.

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from article Wool

Scale formation of Delaine Merino wool fibers.

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from article Wool

Fine wool staples showing distinct crimp (wavy) patterns. The length shown is the minimum for each classification.

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from article Brazil nut

Unshelled Brazil nuts (Bertholletia excelsa). (Photo courtesy of C. E. Timothy Paine)

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from article Cerargyrite

Cerargyrite crystals from Leadville, Colorado. (Specimen from Department of Geology, Bryn Mawr College)

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from article Castor plant

Seeds of the castor plant (Ricinus communis). These seeds, which are also known as castor beans, are processed to make castor oil. (Photo by Brian Prechtel, Agricultural Research Service, United States Department of Agriculture)

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from article Cowpea

Cowpea (Vigna unguiculata): pods and leaves. (Photo by Howard F. Schwartz, Colorado State University)

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from article Cowpea

Cowpea seeds, which are often called black-eyed peas. (Photo by Joseph Berger; Bugwood.org)

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from article Granulite

Southern part of peninsular India and Sri Lanka, showing broad tectonic and metamorphic features. (After A. P. Subramaniam, Charnockites and granulites of southern India: A review, Dan. Geol. Foren., 17:473–493, 1967)

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from article Kumquat

Fruits and foliage of the Nagami kumquat (Fortunella margarita). (Photo by Forest and Kim Starr)

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from article Melilite

Melilite crystals from Vesuvius, Italy. (Specimen from Department of Geology, Bryn Mawr College)

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from article Mulberry

White mulberry (Morus alba). (Photo courtesy of Forest and Kim Starr)

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from article Beech

Leaf on top of bark of American beech (Fagus grandifolia). (Photo courtesy of Robert H. Mohlenbrock, USDA–NRCS PLANTS Database)

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from article Beech

Beechnuts of the American beech (Fagusgrandifolia). (Photo courtesy of Steve Hurst, USDA–NRCS PLANTS Database)

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from article Oil sand

Tar sand deposits in Alberta. 1 mi = 1.6 km.

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from article Lightning

Natural cloud-to-ground lightning near Tucson, Arizona. Note that each discharge strikes the ground in more than one place. (Photo courtesy of Michael J. Leuthold)

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from article Lightning

Sketches of the different types of lightning between an idealized cloud and the ground: (a) type 1, (b) type 2, (c) type 3, and (d) type 4. Channel development within the cloud is not shown. Type 1 is the most common form of cloud-to-ground…

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from article Lightning

Global map showing the average yearly lightning flashes per km2 from 1995 to 2013. The map is based on data collected from 1998–2013 by the Lightning Imaging Sensor (LIS) on NASA’s Tropical Rainfall Measuring Mission satellite, and from 1995–2000 by…

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from article Lightning

Two hundred sensor locations show the total area (shaded) that makeup the North American Lightning Detection Network. The shaded area is defined by any flash location within 600 km of a sensor. Over 30 million cloud-to-ground lightning flashes are…

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from article Lightning

Annual average ground flash density for the North American Lightning Detection Network is shown for 10 years, 2001–2010.

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from article Marjoram

Close-up view of marjoram (Majorana hortensis; alternatively Origanum majorana). (Photo courtesy of Forest and Kim Starr)

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from article Devonian

Devonian, the fourth period of the Paleozoic Era.

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from article Devonian

Biostratigraphic zones based on conodonts (left) plotted to show approximate correspondence to the chronostratigraphic stages and series which compose the Devonian System (right) and relative sea-level changes (center) showing major fluctuations…

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from article Devonian

Reconstruction of Middle Devonian continental positions based on distribution of lithologic climatic indicators. Probable ocean currents derived from this paleogeography explain the biogeographic realms. Kolyma and Tarim are microcontinents of the…

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from article Smog

Smog, Downtown Los Angeles, California, USA. (Credit: Yenwen Lu/Getty Images)

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from article Smog

Average background concentration of ozone in the atmosphere as a function of altitude. Note the enhancement of O3 near the Earth's surface that can occur in polluted areas as a result of photochemical smog.

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from article Chestnut

American chestnut (Castanea dentata). (Photo courtesy of Forest and Kim Starr)

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from article Chestnut

Nuts of the Allegheny chinquapin (Castanea pumila). (Photo courtesy of Steve Hurst, USDA–NRCS PLANTS Database)

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from article Caraway

Caraway (Carum carvi) fruits (often called “seeds”). Scale bar = 1 mm. (Photo by Steve Hurst; USDA–NRCS PLANTS Database)

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from article Microcline

Microcline, variety amazon stone, Pikes Peak, Colorado. (American Museum of Natural History specimen)

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from article Dallis grass

Dallis grass (Paspalum dilatatum). (Photo courtesy of Larry Allain, USGS National Wetlands Research Center)

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from article Oriental vegetables

Bok choy, also known as pak choy or Chinese mustard (Brassica rapa or Brassica campestris, chinensis group). (Photo courtesy of the Agricultural Research Service, U.S. Department of Agriculture)

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from article Oriental vegetables