The Sahara Desert, covering most of North Africa, is the largest desert in the world. From north to south, the Sahara is between 800 and 1,200 miles and is at least 3,000 miles (4,800 km) from east to west. Due to the massive size of the Sahara, Africa is split into two regions that which lies above or forms part of the Sahara and the rest of Africa, south of the Sahara (ThinkQuest Team, 1998). Some of the Sahara deserts geological features would include butte, blowout, and loess, as illustrated above.
Butte
It is a narrow, flat-topped hill of resistant rock with very steep sides and probably a former mesa (Katz, 2010). This landform is most often composed of sedimentary rock, formed by the accumulation and compression of sediment. The top layer is a hardened layer of rock that is resistant to erosion, which is the gradual wearing away of Earth surfaces through the action of wind and water. Sometimes this top layer, called the cap rock, is not sedimentary rock but is cooled and hardened lava that had spread out across the landscape in repeated flows from fissures or cracks in the ground (Mesa, 2010).
Going to the Sun Road, Glacier National Park
Source
Above is a picture of mountain ranges in Glacier National Park. It is a photo taken by a person going to the Sun Road.
Horns
When three or more corries erode backwards and meet, they cannot form an arete it has steep sides but does not have the length to make a ridge. Imagine three corries at the corners of a triangle, eventually all eroding back and meeting in the middle. A sharp pointed pyramid shape is created. This is called a pyramidal peak, or horn, and is a common shape for mountain tops in well-glaciated areas (Aretes, 2006).
Arete
It is a steep-sided, sharp-edged bedrock ridge formed by two glaciers eroding away on opposite sides of the ridge (Lemke, 1998). When a corrie is formed, its back and side walls tend to be steep and jagged, perhaps almost vertical. When two corries form next to each other, and their adjacent walls are eroded backwards until they meet, a narrow and pointed rock ridge is formed. This is often likened to a knife edge, with near vertical sides and a sharp top edge. This feature is called an arete (Aretes, 2006).
U-shaped valley
U-shaped valleys often start as river valleys that existed before glaciation occurred. The glaciers then followed the existing V-shaped valleys, eroding and deepening them as the ice moved. Over time the valleys become straightened, widened and deepened, keeping the steep sides and acquiring a flat base. U-shaped valleys are also known as glacial troughs (U-shaped, 2006).
Source
The central part of Panum Crater is a rhyolite dome, formed around 650 years ago by slow rising of viscous, relatively cool magma, rich in silica, hence the high obsidian content of the resulting rocks. Surrounding the dome is a tufa ring, slightly lower in height, composed of ash and pumice ejected from the vent in an earlier, more violent stage of the eruption. The narrow spires seen today on top of the dome were created when the main mass had cooled and hardened, but the residual lava below still had enough force to split the surface and extrude into pinnacles (Crossley).
Crater
A volcanic crater is a circular-lowered ground caused by volcanic activity at the top of the volcano, the opening of the volcano. It is a circular basin in which magma erupts as gases, lava and ejecta. It can be in various sizes and various depths. In majority, craters occur from volcanic deposits such as lava flows and tephra.
Dome
A lava dome occurs when the volcano rebuilds itself. Domes are roughly circular-shaped protrusion resulting from the slow extrusion during the eruption of the volcano. It forms mostly within the crater. The dome shape occurs because of the high viscosity that prevents the lava to flow very far. Domes may reach heights of several hundred meters, and can grow slowly and steadily for months.
Tephra (Ejecta) Ring The ejecta ring is made up of small bits of pumice, ash, obsidian fragments, and well-rounded granitic pebbles (which are part of the surrounding rock and not formed during the eruption) that are ejected during the final explosive stage of the eruption.
Butte
It is a narrow, flat-topped hill of resistant rock with very steep sides and probably a former mesa (Katz, 2010). This landform is most often composed of sedimentary rock, formed by the accumulation and compression of sediment. The top layer is a hardened layer of rock that is resistant to erosion, which is the gradual wearing away of Earth surfaces through the action of wind and water. Sometimes this top layer, called the cap rock, is not sedimentary rock but is cooled and hardened lava that had spread out across the landscape in repeated flows from fissures or cracks in the ground (Mesa, 2010).
Going to the Sun Road, Glacier National Park
Source
Above is a picture of mountain ranges in Glacier National Park. It is a photo taken by a person going to the Sun Road.
Horns
When three or more corries erode backwards and meet, they cannot form an arete it has steep sides but does not have the length to make a ridge. Imagine three corries at the corners of a triangle, eventually all eroding back and meeting in the middle. A sharp pointed pyramid shape is created. This is called a pyramidal peak, or horn, and is a common shape for mountain tops in well-glaciated areas (Aretes, 2006).
Arete
It is a steep-sided, sharp-edged bedrock ridge formed by two glaciers eroding away on opposite sides of the ridge (Lemke, 1998). When a corrie is formed, its back and side walls tend to be steep and jagged, perhaps almost vertical. When two corries form next to each other, and their adjacent walls are eroded backwards until they meet, a narrow and pointed rock ridge is formed. This is often likened to a knife edge, with near vertical sides and a sharp top edge. This feature is called an arete (Aretes, 2006).
U-shaped valley
U-shaped valleys often start as river valleys that existed before glaciation occurred. The glaciers then followed the existing V-shaped valleys, eroding and deepening them as the ice moved. Over time the valleys become straightened, widened and deepened, keeping the steep sides and acquiring a flat base. U-shaped valleys are also known as glacial troughs (U-shaped, 2006).
Source
The central part of Panum Crater is a rhyolite dome, formed around 650 years ago by slow rising of viscous, relatively cool magma, rich in silica, hence the high obsidian content of the resulting rocks. Surrounding the dome is a tufa ring, slightly lower in height, composed of ash and pumice ejected from the vent in an earlier, more violent stage of the eruption. The narrow spires seen today on top of the dome were created when the main mass had cooled and hardened, but the residual lava below still had enough force to split the surface and extrude into pinnacles (Crossley).
Crater
A volcanic crater is a circular-lowered ground caused by volcanic activity at the top of the volcano, the opening of the volcano. It is a circular basin in which magma erupts as gases, lava and ejecta. It can be in various sizes and various depths. In majority, craters occur from volcanic deposits such as lava flows and tephra.
Dome
A lava dome occurs when the volcano rebuilds itself. Domes are roughly circular-shaped protrusion resulting from the slow extrusion during the eruption of the volcano. It forms mostly within the crater. The dome shape occurs because of the high viscosity that prevents the lava to flow very far. Domes may reach heights of several hundred meters, and can grow slowly and steadily for months.
Tephra (Ejecta) Ring The ejecta ring is made up of small bits of pumice, ash, obsidian fragments, and well-rounded granitic pebbles (which are part of the surrounding rock and not formed during the eruption) that are ejected during the final explosive stage of the eruption.
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