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Joints arise from brittle fracture of a rock or layer due to tensile stress.This stress may be imposed from outside; for example, by the stretching of layers, the rise of pore fluid pressure, or shrinkage caused by the cooling or desiccation of a rock body or layer whose outside boundaries remained fixed.
Columnar jointing is a geological structure where sets of intersecting closely spaced fractures, referred to as joints, result in the formation of a regular array of polygonal prisms (basalt prisms), or columns. Columnar jointing occurs in many types of igneous rocks and forms as the rock cools and contracts.
Basalt columns seen on Porto Santo Island, Portugal. Columnar jointing of volcanic rocks exists in many places on Earth. Perhaps the most famous basalt lava flow in the world is the Giant's Causeway in Northern Ireland, in which the vertical joints form polygonal columns and give the impression of having been artificially constructed.
Systematic Joints are joint systems in which all the joints are parallel or subparallel, and maintain roughly the same spacing from each other. Columnar Joints are joints that cut the formation vertically in (typically) hexagonal columns. These tend to be a result of cooling and contraction in hypabyssal intrusions or lava flows.
Triangle Dome displays a pattern of columnar cooling joints that indicates it was formed by volcanic activity in a subglacial environment. [32] A 24-metre-thick (79-foot) trachyte flow that may have issued during an early, fluid phase of the Glacier Dome eruption is exposed for 2 kilometres (1.2 miles) north of Pyramid Creek; its distal end ...
Spheroidal weathering of exposed sections of the dykes has focussed on cooling joints present within the body of intrusive rock. Radiometric dating of the dykes has returned ages of around 52 million years for their emplacement though an older age of around 61 million years has also been suggested by measurements.
In geotechnical engineering, a discontinuity (often referred to as a joint) is a plane or surface that marks a change in physical or chemical characteristics in a soil or rock mass. A discontinuity can be, for example, a bedding , schistosity , foliation , joint , cleavage , fracture , fissure , crack, or fault plane.
In geology and geophysics, thermal subsidence is a mechanism of subsidence in which conductive cooling of the mantle thickens the lithosphere and causes it to decrease in elevation. This is because of thermal expansion : as mantle material cools and becomes part of the mechanically rigid lithosphere, it becomes denser than the surrounding material.