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Perched Coastline
A perched coastline is a fossil coastline currently above the present coastline. It can be produced by one of two factors: * Higher sea levels in the past than today. For example, during the last ice age interglacial period, climates were significantly warmer than today, and thermal expansion of the oceans, together with increased melting of glaciers, meant that sea levels were higher than they are today. This has created evidence of perched coastlines all around the world. * Through coastal uplift from local geological processes, particularly along the edges of rift valleys or subduction zones of tectonic plates. This second kind of perched coastline is important archaeologically, as it can expose human remains that would otherwise be below sea level. See also * Paleoshoreline A paleoshoreline (ancient shoreline) is a shoreline which existed in the geologic past. (''Paleo'' is from an ancient Greek word meaning "old" or "ancient".) A perched coastline is an ancient (fo ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Fossil Coastline
A paleoshoreline (ancient shoreline) is a shoreline which existed in the geologic past. (''Paleo'' is from an ancient Greek word meaning "old" or "ancient".) A perched coastline is an ancient (fossil) shoreline positioned above the present shoreline. Tides cause the ocean to advance and recede in a very short time scale, in most places about twice per day; weather conditions can also cause short-term variations. Coastlines can also move due to coastal erosion, without a change in sea level. But "sea level" refers to the average level over a relatively long period (years). This average sea level can advance and recede over much longer periods (thousands or millions of years), causing paleoshorelines which may be difficult to identify. Just off the coast of parts of North America, in the last 15,000 years sea level has varied from over below, to as high as above its present level. That entire time, humans have lived in North America. A lake may also have a paleoshoreline. Pal ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Interglacial
An interglacial period (or alternatively interglacial, interglaciation) is a geological interval of warmer global average temperature lasting thousands of years that separates consecutive glacial periods within an ice age. The current Holocene interglacial began at the end of the Pleistocene, about 11,700 years ago. Pleistocene During the 2.5 million years of the Pleistocene, numerous glacials, or significant advances of continental ice sheets, in North America and Europe, occurred at intervals of approximately 40,000 to 100,000 years. The long glacial periods were separated by more temperate and shorter interglacials. During interglacials, such as the present one, the climate warms and the tundra recedes polewards following the ice sheets. Forests return to areas that once supported tundra vegetation. Interglacials are identified on land or in shallow epicontinental seas by their paleontology. Floral and faunal remains of species pointing to temperate climate and indicating a s ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Thermal Expansion
Thermal expansion is the tendency of matter to change its shape, area, volume, and density in response to a change in temperature, usually not including phase transitions. Temperature is a monotonic function of the average molecular kinetic energy of a substance. When a substance is heated, molecules begin to vibrate and move more, usually creating more distance between themselves. Substances which contract with increasing temperature are unusual, and only occur within limited temperature ranges (see examples below). The relative expansion (also called strain) divided by the change in temperature is called the material's coefficient of linear thermal expansion and generally varies with temperature. As energy in particles increases, they start moving faster and faster weakening the intermolecular forces between them, therefore expanding the substance. Overview Predicting expansion If an equation of state is available, it can be used to predict the values of the thermal expan ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Glacier
A glacier (; ) is a persistent body of dense ice that is constantly moving under its own weight. A glacier forms where the accumulation of snow exceeds its Ablation#Glaciology, ablation over many years, often Century, centuries. It acquires distinguishing features, such as Crevasse, crevasses and Serac, seracs, as it slowly flows and deforms under stresses induced by its weight. As it moves, it abrades rock and debris from its substrate to create landforms such as cirques, moraines, or fjords. Although a glacier may flow into a body of water, it forms only on land and is distinct from the much thinner sea ice and lake ice that form on the surface of bodies of water. On Earth, 99% of glacial ice is contained within vast ice sheets (also known as "continental glaciers") in the polar regions, but glaciers may be found in mountain ranges on every continent other than the Australian mainland, including Oceania's high-latitude oceanic island countries such as New Zealand. Between lati ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Sea Level
Mean sea level (MSL, often shortened to sea level) is an average surface level of one or more among Earth's coastal bodies of water from which heights such as elevation may be measured. The global MSL is a type of vertical datuma standardised geodetic datumthat is used, for example, as a chart datum in cartography and marine navigation, or, in aviation, as the standard sea level at which atmospheric pressure is measured to calibrate altitude and, consequently, aircraft flight levels. A common and relatively straightforward mean sea-level standard is instead the midpoint between a mean low and mean high tide at a particular location. Sea levels can be affected by many factors and are known to have varied greatly over geological time scales. Current sea level rise is mainly caused by human-induced climate change. When temperatures rise, Glacier, mountain glaciers and the Ice sheet, polar ice caps melt, increasing the amount of water in water bodies. Because most of human settlem ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Rift Valley
A rift valley is a linear shaped lowland between several highlands or mountain ranges created by the action of a geologic rift. Rifts are formed as a result of the pulling apart of the lithosphere due to extensional tectonics. The linear depression may subsequently be further deepened by the forces of erosion. More generally the valley is likely to be filled with sedimentary deposits derived from the rift flanks and the surrounding areas. In many cases rift lakes are formed. One of the best known examples of this process is the East African Rift. On Earth, rifts can occur at all elevations, from the sea floor to plateaus and mountain ranges in continental crust or in oceanic crust. They are often associated with a number of adjoining subsidiary or co-extensive valleys, which are typically considered part of the principal rift valley geologically. Earth's rift valleys The most extensive rift valley is located along the crest of the mid-ocean ridge system and is the result of s ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Subduction Zone
Subduction is a geological process in which the oceanic lithosphere is recycled into the Earth's mantle at convergent boundaries. Where the oceanic lithosphere of a tectonic plate converges with the less dense lithosphere of a second plate, the heavier plate dives beneath the second plate and sinks into the mantle. A region where this process occurs is known as a subduction zone, and its surface expression is known as an arc-trench complex. The process of subduction has created most of the Earth's continental crust. Rates of subduction are typically measured in centimeters per year, with the average rate of convergence being approximately two to eight centimeters per year along most plate boundaries. Subduction is possible because the cold oceanic lithosphere is slightly denser than the underlying asthenosphere, the hot, ductile layer in the upper mantle underlying the cold, rigid lithosphere. Once initiated, stable subduction is driven mostly by the negative buoyancy of the dens ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Tectonic Plate
Plate tectonics (from the la, label=Late Latin, tectonicus, from the grc, τεκτονικός, lit=pertaining to building) is the generally accepted scientific theory that considers the Earth's lithosphere to comprise a number of large tectonic plates which have been slowly moving since about 3.4 billion years ago. The model builds on the concept of ''continental drift'', an idea developed during the first decades of the 20th century. Plate tectonics came to be generally accepted by geoscientists after seafloor spreading was validated in the mid to late 1960s. Earth's lithosphere, which is the rigid outermost shell of the planet (the crust and upper mantle), is broken into seven or eight major plates (depending on how they are defined) and many minor plates or "platelets". Where the plates meet, their relative motion determines the type of plate boundary: '' convergent'', '' divergent'', or ''transform''. Earthquakes, volcanic activity, mountain-building, and oceanic tren ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Paleoshoreline
A paleoshoreline (ancient shoreline) is a shoreline which existed in the geologic past. (''Paleo'' is from an ancient Greek word meaning "old" or "ancient".) A perched coastline is an ancient (fossil) shoreline positioned above the present shoreline. Tides cause the ocean to advance and recede in a very short time scale, in most places about twice per day; weather conditions can also cause short-term variations. Coastlines can also move due to coastal erosion, without a change in sea level. But "sea level" refers to the average level over a relatively long period (years). This average sea level can advance and recede over much longer periods (thousands or millions of years), causing paleoshorelines which may be difficult to identify. Just off the coast of parts of North America, in the last 15,000 years sea level has varied from over below, to as high as above its present level. That entire time, humans have lived in North America. A lake may also have a paleoshoreline. Pal ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Coastal Geography
Coastal geography is the study of the constantly changing region between the ocean and the land, incorporating both the physical geography (i.e. coastal geomorphology, climatology and oceanography) and the human geography (sociology and history) of the coast. It includes understanding coastal weathering processes, particularly wave action, sediment movement and weather, and the ways in which humans interact with the coast. Wave action and longshore drift The waves of different strengths that constantly hit against the shoreline are the primary movers and shapers of the coastline. Despite the simplicity of this process, the differences between waves and the rocks they hit result in hugely varying shapes. The effect that waves have depends on their strength. Strong waves, also called destructive waves, occur on high-energy beaches and are typical of winter. They reduce the quantity of sediment present on the beach by carrying it out to bars under the sea. Constructive, weak waves ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
