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|Devils Tower National Monument|
Devils Tower, 1900
|Location||Crook County, Wyoming, USA|
|Nearest city||Hulett, Wyoming|
|Area||1,346.91 acres (5.45 km2)|
|Established||September 24, 1906|
|Visitors||386,558 (in 2004)|
|Governing body||National Park Service|
Devils Tower is a monolithic igneous intrusion or volcanic neck located in theBlack Hills near Hulett and Sundance in Crook County, northeastern Wyoming, above the Belle Fourche River. It rises dramatically 1,267 feet (386 m) above the surrounding terrain and the summit is 5,112 feet (1,558 m) above sea level.
Devils Tower was the first declared United States National Monument, established on September 24, 1906, by President Theodore Roosevelt. The Monument's boundary encloses an area of 1,347 acres (5.45 km2).
Theories of formation G
Uluru is an inselberg, literally "island mountain", an isolated remnant left after the slow erosion of an original mountain range. Uluru is also often referred to as a monolith, although this is a somewhat ambiguous term that is generally avoided by geologists. The remarkable feature of Uluru is its homogeneity and lack of jointing and parting at bedding surfaces, leading to the lack of development of scree slopes and soil. These characteristics led to its survival, while the surrounding rocks were eroded. For the purpose of mapping and describing the geological history of the area, geologists refer to the rock strata making up Uluru as the Mutitjulu Arkose, and it is one of many sedimentary formationsfilling the Amadeus Basin.
Uluru is dominantly composed of coarse-grained arkose, a type of sandstone characterized by an abundance of feldspar, and some conglomerate.Average composition is 50% feldspar, 25–35% quartz and up to 25% rock fragments; most feldspar is K-feldspar with only minor plagioclase as subrounded grains and highly altered inclusions within K-feldspar.The grains are typically 2–4 millimetres (0.079–0.16 in) in diameter, and are angular to subangular; the finer sandstone is well sorted, with sorting decreasing with increasing grain size. The rock fragments include subrounded basalt, invariably replaced to various degrees by chlorite and epidote. The minerals present suggest derivation from a predominantly granite source, similar to the Musgrave Block exposed to the south. When relatively fresh, the rock has a grey colour, but weathering of iron-bearing minerals by the process of oxidation gives the outer surface layer of rock a red-brown rusty colour. Features related to deposition of the sediment include cross-bedding and ripples, analysis of which indicated deposition from broad shallow high energy fluvial channels and sheet flooding, typical of alluvial fans.
Age and origin
The Mutitjulu Arkose is believed to be of about the same age as the conglomerate at Kata Tjuta, and to have a similar origin despite the rock type being different, but it is younger than the rocks exposed to the east at Mount Conner, and unrelated to them. The strata at Uluru are nearly vertical, dipping to the south west at 85°, and have an exposed thickness of at least 2,400 m (7,900 ft). The strata dip below the surrounding plain and no doubt extend well beyond Uluru in the subsurface, but the extent is not known. The rock was originally sand, deposited as part of an extensive alluvial fan that extended out from the ancestors of the Musgrave, Mann and Petermann Ranges to the south and west, but separate from a nearby fan that deposited the sand, pebbles and cobbles that now make up Kata Tjuta. The similar mineral composition of the Mutitjulu Arkose and the granite ranges to the south is now explained. The ancestors of the ranges to the south were once much larger than the eroded remnants we see today. They were thrust up during a mountain building episode referred to as the Petermann Orogeny that took place in late Neoproterozoic to early Cambrian times (550-530 Ma), and thus the Mutitjulu Arkose is believed to have been deposited at about the same time. The arkose sandstone which makes up the formation is composed of grains that show little sorting based on grain size, exhibit very little rounding and the feldspars in the rock are relatively fresh in appearance. This lack of sorting and grain rounding is typical of arkosic sandstones and is indicative of relatively rapid erosion from the granites of the growing mountains to the south. The layers of sand were nearly horizontal when deposited, but were tilted to their near vertical position during a later episode of mountain building, possibly the Alice Springs Orogeny of Palaeozoic age (400-300 Ma).
ARCHES NATIONAL PARK
Arches National Park is a U.S. National Park in eastern Utah. It is known for preserving over 2000 natural sandstone arches, including the world-famous Delicate Arch, in addition to a variety of unique geological resources and formations.
The park is located just outside of Moab, Utah, and is 119 square miles (310 km2) in size. Its highest elevation is 5,653 feet (1,723 m) at Elephant Butte, and its lowest elevation is 4,085 feet (1,245 m) at the visitor center. Forty-three arches have collapsed due to erosion since 1970. The park receives 10 inches (250 mm) of rain a year on average.
The national park lies atop an underground evaporite layer or salt bed, which is the main cause of the formation of the arches, spires, balanced rocks, sandstone fins, and eroded monoliths in the area. This salt bed is thousands of feet thick in places, and was deposited in the Paradox Basin of the Colorado Plateau some 300 million years ago when a sea flowed into the region and eventually evaporated. Over millions of years, the salt bed was covered with debris eroded from theUncompahgre Uplift to the northeast. During the Early Jurassic (about 210 Ma) desert conditions prevailed in the region and the vast Navajo Sandstone was deposited. An additional sequence of stream laid and windblown sediments, the Entrada Sandstone (about 140 Ma), was deposited on top of the Navajo. Over 5000 feet (1500 m) of younger sediments were deposited and have been mostly eroded away. Remnants of the cover exist in the area including exposures of the CretaceousMancos Shale. The arches of the area are developed mostly within the Entrada formation.
The weight of this cover caused the salt bed below it to liquefy and thrust up layers of rock into salt domes. The evaporites of the area formed more unusual salt anticlines or linear regions of uplift.Faulting occurred and whole sections of rock subsided into the areas between the domes. In some places, they turned almost on edge. The result of one such 2,500-foot (760 m) displacement, theMoab Fault, is seen from the visitor center.
As this subsurface movement of salt shaped the landscape, erosion removed the younger rock layers from the surface. Except for isolated remnants, the major formations visible in the park today are the salmon-colored Entrada Sandstone, in which most of the arches form, and the buff-coloredNavajo Sandstone. These are visible in layer cake fashion throughout most of the park. Over time, water seeped into the surface cracks, joints, and folds of these layers. Ice formed in the fissures, expanding and putting pressure on surrounding rock, breaking off bits and pieces. Winds later cleaned out the loose particles. A series of free-standing fins remained. Wind and water attacked these fins until, in some, the cementing material gave way and chunks of rock tumbled out. Many damaged fins collapsed. Others, with the right degree of hardness and balance, survived despite their missing sections. These became the famous arches.
Satellite photo of Death Valley
|Floor elevation||−282 ft (−86 m)|
Death Valley is a desert valley located in Eastern California. Situated within the Mojave Desert, it features the lowest, driest, and hottest locations in North America. Badwater, a basin located in Death Valley, is the specific location (36° 15' N 116° 49.5' W) of the lowestelevation in North America at 282 feet (86.0 m) below sea level. This point is only 84.6 miles (136.2 km) ESE of Mount Whitney, the highest point in the contiguous United States with an elevation of 14,505 feet (4,421 m). Death Valley holds the record for the highest reliably reported temperature in the Western hemisphere, 134 °F (56.7 °C) at Furnace Creek on July 10, 1913—just short of the world record, 136 °F (57.8 °C) in Al 'Aziziyah, Libya, on September 13, 1922.
Located near the border of California and Nevada, in the Great Basin, east of the Sierra Nevada mountains, Death Valley constitutes much of Death Valley National Park and is the principal feature of the Mojave and Colorado Deserts Biosphere Reserve. It is located mostly in Inyo County, California. It runs from north to south between the Amargosa Range on the east and the Panamint Range on the west; the Sylvania Mountains and the Owlshead Mountains form its northern and southern boundaries, respectively. It has an area of about 3,000 sq mi (7,800 km2). Death Valley shares many characteristics with other places below sea level.
Death Valley is one of the best geological examples of a basin and range configuration. It lies at the southern end of a geological troughknown as Walker Lane, which runs north into Oregon. The valley is bisected by a right lateral strike slip fault system, represented by theDeath Valley Fault and the Furnace Creek Fault. The eastern end of the left lateral Garlock Fault intersects the Death Valley Fault. Furnace Creek and the Amargosa River flow through the valley but eventually disappear into the sands of the valley floor.
Death Valley also contains salt pans. According to current geological consensus, during the middle of the Pleistocene era there was a succession of inland seas (collectively referred to as Lake Manly) located where Death Valley is today. As the area turned to desert the water evaporated, leaving behind the abundance of evaporitic salts such as common sodium salts and borax, which were subsequently exploited during the modern history of the region, primarily 1883 to 1907.
As a general rule, lower altitudes tend to have higher temperatures where the sun heats the ground and that heat is then radiated upward, but as the air begins to rise it is trapped by (1) the surrounding elevation and (2) the weight of the air (essentially the atmospheric pressure) above it. The atmospheric pressure is higher at very low altitudes than it is under the same conditions at sea level because there is more air (more distance) between the ground and the top of the atmosphere. This pressure traps the heat near the ground, and also creates wind currents that circulate very hot air, thereby distributing the heat to all areas, regardless of shade and other factors.
This process is especially important in Death Valley as it provides its specific climate and geography. The valley is surrounded by mountains, while its surface is mostly flat and devoid of plants, and of which a high percentage of the sun's heat is able to reach the ground, absorbed by soil and rock. When air at ground level is heated, it begins to rise, moving up past steep high mountain ranges, which then cools slightly, sinking back down towards the valley more compressed. This air is then reheated by the sun to a higher temperature, moving up the mountain again, whereby the air moves up and down in a circular motion in cycles, similar to how a convection oven works, albeit a natural one. This superheated air increases ground temperature markedly, forming the hot wind currents that are trapped by atmospheric pressure and mountains, thus stays mostly within the valley. Such hot wind currents contribute to perpetual drought-like conditions in Death Valley and prevent much cloud formation to pass through the confines of the valley, where precipitation is often in the form of a virga. Death Valley holds temperature records because it has an unusually high number of factors that lead to high atmospheric temperatures.