boulder

boulder, large rock fragment formed by detachment from its parent consolidated rock by weathering and erosion. In engineering and geology, especially in the United States, the term is applied to loose rocks having specific sizes according to various systems of classification, i.e. the Wentworth scale (for C. K. Wentworth, American geologist), where a boulder has one linear dimension of at least 10.1 in. (25.4 cm). Boulders transported by glacial ice are usually referred to as glacial erratics; glacial boulder fields, or felsenmeer, containing large blocks of angular rock broken from intense frost action are evidence that the region has experienced glacial action in the past. See drift; moraine.

In geology, the unsorted material deposited directly by glacial ice and showing no stratification. Till is sometimes called boulder clay because it is composed of clay, boulders of intermediate size, or both. The rock fragments are usually angular and sharp rather than rounded, because they are deposited from ice and have undergone little water transport. The pebbles and boulders may be faceted and striated from grinding while lodged in the glacier.

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or till-less agriculture

Cultivation technique in which the soil is disturbed only along the slit or hole into which seeds are planted. Reserved detritus from previous crops covers and protects the seedbed. Primary benefits are a decreased rate of soil erosion; reduced need for equipment, fuel, and fertilizer; and significantly less time required for tending crops. The method also improves soil-aggregate formation, microbial activity in the soil, and water infiltration and storage. Conventional tillage controls weed growth by plowing and cultivating, but no-till farming selectively uses herbicides to kill weeds and the remains of the previous crop. No-till farming is one of several primitive farming methods revived as conservation measures in the 20th century.

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German peasant trickster of folk and literary tales. The historical Till is said to have died in 1350; anecdotes associated with his name were printed circa 1500 in Low German and from 1515 in High German. In the tales the stupid yet cunning peasant demonstrates his superiority to the narrow, dishonest, condescending townsmen, as well as to the clergy and nobility. The tales were translated into Dutch and English (circa 1520), French (1532), and Latin (1558).

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formerly Boulder Dam

Highest concrete arch dam in the U.S., built on the Colorado River at the Arizona-Nevada border. It impounds Lake Mead. The dam, completed in 1936, is used for flood and silt control, electric power, irrigation, and domestic and industrial water supplies. It is 726 ft (221 m) high and 1,244 ft (379 m) long (along the crest), has a power capacity of 1,345 megawatts, and a volume of 4.4 million cu yd (3.36 million cu m).

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City (pop., 2000: 94,673), north-central Colorado, U.S. Located at the base of the Rocky Mountains northwest of Denver, it was settled by miners in 1858 and grew with the arrival of two railroads in 1873. An extensive government-industrial-educational complex has developed since the 1950s. It is the site of the University of Colorado.

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In geology, a boulder is a rock with grain size of usually no less than 256 mm (10 inches) diameter. While a boulder may be small enough to move or roll manually, others are extremely massive. In common usage, a boulder is too large for a person to move. Smaller boulders are usually just called rocks or stones. The word boulder comes from Middle English "bulder" which was probably of Scandinavian origin such as dialectal Swedish "bullersten" meaning "noisy stone" (Imagine a large stone in a stream, causing water to roar around it) from "bullra" (to roar, cf. Dutch "bulderen", with the same meaning) and "sten" (stone).

In places covered by ice sheets during Ice Ages, such as Scandinavia, northern North America, and Russia, ice has moved and formed granite boulders, also named glacial erratics. One of the largest is used as the pedestal of the Bronze Horseman in Saint Petersburg, Russia.

Some noted rock formations involve giant boulders exposed by erosion, such as the Devil's Marbles in Australia's Northern Territory, the Wairere Boulders in New Zealand, where an entire valley contains only boulders, and The Baths on the island of Virgin Gorda in the British Virgin Islands.

The climbing of large boulders often requires developing special abilities, and has given rise, since the late 19th century, to the sport of bouldering.