https://padlet.com/21297242/1oy1xajgy8z5 Emma Croteau / Honors Earth Science / Block 3 / Wednesday, November 1st, 2017 en-us 2017-11-03 16:33:36 UTC 2017-11-08 15:58:44 UTC hello@padlet.com 21297242 https://padlet.com/21297242/1oy1xajgy8z5/wish/203378699 These are often formed through wind on beaches or in deserts. When wind blows sand against an object or obstacle in a sheltered area, the dunes continue to grow as the grains of sand blown accumulate to form the dunes. The windward side of a dune is the side where the wind blows against and pushes the sand up. The slip side of a dune is the side which is not facing the wind, resulting in it having a smoother surface. Many dunes together (like the ones shown below) are known as a dune belt or field.]]> 2017-11-03 16:39:38 UTC https://padlet.com/21297242/1oy1xajgy8z5/wish/203378699 21297242 https://padlet.com/21297242/1oy1xajgy8z5/wish/203379915 These distinct rock formations are formed through various weathering and erosion processes, those being frost wedging and erosion from (slightly acidic) rainwater. Because of this, hoodoos are often found in High Plateaus regions in North America that have continuous freezing and eroding cycles. Hoodoos originate from larger rock areas and then break off over time due to their forced expansion from frost wedging. As they continue to break off and crack, the resistant layer allows the softer rock to erode underneath. Then, when that "cap" of the resistant rock layer remains, it provides protection for some of that soft layer. The rainwater, often being acidic, is able to meticulously dissolve the rock grain by grain and round/shape the edges of the hoodoo. ]]> 2017-11-03 16:41:56 UTC https://padlet.com/21297242/1oy1xajgy8z5/wish/203379915 21297242 https://padlet.com/21297242/1oy1xajgy8z5/wish/203380829 Many pinnacles occur in desert areas, as seen in the ones below. These pinnacles are formed through an extensive process. First, many sand grains are comprised of small grains of quartz and calcite. When it rains in these areas, the moisture dissolves and leeches the calcite from the sand's upper levels, as it precipitates it into cement from its lower levels. Over time, a layer of calcrete is formed which separates the surface layer from the lower layers. This calcrete layer is then broken apart by cracks and plant roots, which allows the rain to dissolve further into calcite layers. Thus the areas become enriched in quartz sand, allowing the leaching zones to form low spots between pinnacles with calcrete caps. Finally, through the use of wind erosion, the sediment is removed during the process of gradual deflation and, as the cracks breach the caliche capping, the wind erodes away the excess sand, leaving the pinnacles.]]> 2017-11-03 16:43:32 UTC https://padlet.com/21297242/1oy1xajgy8z5/wish/203380829 21297242 https://padlet.com/21297242/1oy1xajgy8z5/wish/203960420 Arches first began to form when the wrinkling and folding of buried sandstone began, producing anticlines and, as it was warped, tearing fractures through it and establishing patterns of rock layers. Erosion forces (such as rain, wind, etc.) carves away these rock layers that later rebound and expand after being exposed. These create more fractures which allow for frost wedging and water erosion to occur. The frost wedging breaks off many chunks of sandstone from the rock, while the rain erodes it and carries away sediments. As recesses develop in the rock because of these processes, they continue to expand and turn the fractured rock layers into fins and then arches. Potholes near cliff edges also grow bigger because of erosion until they wear through the cliff rock below and form an arch.]]> 2017-11-06 16:10:12 UTC https://padlet.com/21297242/1oy1xajgy8z5/wish/203960420 21297242 https://padlet.com/21297242/1oy1xajgy8z5/wish/203961262 Talus slopes are formed due to the accumulation of loose, coarse, and mostly angular rock debris at the foot of bare rock slopes. This mostly occurs in environments where physical weathering processes are common and gravitational processes allow for the down slope (present here). There are two main processes that can result in the formation of talus slopes. The first being where detachment of granite pieces from vertical edges (because of frost wedging or tree roots, etc.) cause them to slide and wear down. The second process occurs due to the accumulation of debris on irregular cliff surfaces, leading to rock deposition. Snow avalanches, surface water flow, and animals are also contributing factors. ]]> 2017-11-06 16:11:32 UTC https://padlet.com/21297242/1oy1xajgy8z5/wish/203961262 21297242 https://padlet.com/21297242/1oy1xajgy8z5/wish/203962193 V-shaped valleys are mainly due to water erosion by rivers and other forms of water flow. These processes occur in mountain ranges, where rivers have steep gradients, and thus produce steep walls and bottoms for the hills they erode. The fast-flowing rivers have more dominant vertical erosion in their upper course, thus quickly removing sediment from the bottom of the stream channel rather than the sides. This process is known as down cutting. ]]> 2017-11-06 16:13:00 UTC https://padlet.com/21297242/1oy1xajgy8z5/wish/203962193 21297242 https://padlet.com/21297242/1oy1xajgy8z5/wish/203964019 These are formed when a stream and its water flow erodes the outer river banks, thus widening the valley it is located in. When this occurs, the moving water in the center of the river has less energy flow, which leads to the deposition of silt. This is all due to the fact that "a stream of any volume may assume a meandering course, alternately eroding sediments from the outside of a bend and depositing them on the inside" (Stolum, Hans Henrik, 1998). ]]> 2017-11-06 16:15:45 UTC https://padlet.com/21297242/1oy1xajgy8z5/wish/203964019 21297242 https://padlet.com/21297242/1oy1xajgy8z5/wish/204664920 Ox-bow lakes are formed from meandering streams which become very curved over time. As the neck of the meander grows increasingly narrow, the river cuts along the neck during times of flooding, separating it. The lake is thus formed due to erosion by water flow.]]> 2017-11-08 03:48:08 UTC https://padlet.com/21297242/1oy1xajgy8z5/wish/204664920 21297242 https://padlet.com/21297242/1oy1xajgy8z5/wish/204665073 These occur when an underground layer of rock is dissolved by acidic water when rainfall leeks through the soil, reacting with decaying vegetation and carbon dioxide present. As this now acidic water erodes away at the lower rock layers, cavernous spaces in the ground are created. This eventually leads to the collapse of the upper layers, and thus the hole in the earth. Which often is smoothed due to erosion by wind and water.]]> 2017-11-08 03:49:01 UTC https://padlet.com/21297242/1oy1xajgy8z5/wish/204665073 21297242 https://padlet.com/21297242/1oy1xajgy8z5/wish/204665218 Both are formed primarily in caves due to water erosion, which leads to mineral deposition. As water flows from the upper ground overhead, it leaks into the cave and its cracks, where it dissolves a mineral called calcite. This dripping water leaves behind these traces of calcite, which continue to build up until they form the stalactites. As even more water drips from these stalactites, the calcite accumulates in piles on cave floors. These, over time, form the cone-like structures of stalagmites. ]]> 2017-11-08 03:50:08 UTC https://padlet.com/21297242/1oy1xajgy8z5/wish/204665218 21297242 https://padlet.com/21297242/1oy1xajgy8z5/wish/204665527 These narrow ridges of rock separating two valleys are often formed due to glacier erosion and collision. When two glaciers erode parallel to one another in a u-shaped valley, this rock ridge is formed. It becomes more defined and steep over time (as seen below) due to weathering processes, such as erosion by wind and water. As the glacier passes both sides of a mountain, it wears down the rock and forms a sharp, jagged edge. ]]> 2017-11-08 03:52:06 UTC https://padlet.com/21297242/1oy1xajgy8z5/wish/204665527 21297242 https://padlet.com/21297242/1oy1xajgy8z5/wish/204665705 These result from arêtes that have gone through more extensive erosion processes. When at least three or more arêtes which diverge from a certain point are eroded by glacial flow, a sharp-edged peak is formed.]]> 2017-11-08 03:53:08 UTC https://padlet.com/21297242/1oy1xajgy8z5/wish/204665705 21297242 https://padlet.com/21297242/1oy1xajgy8z5/wish/204666205 These are often due to trough valleys or glacial troughs, also known as glaciation. When a large glacier travels across and down a mountain slope, it carves out the valley through a scoring process. Over time, this results in its characteristic shape of steep, straight sides and a relatively flat bottom that only the sleek sides of glacial ice can produce. ]]> 2017-11-08 03:56:39 UTC https://padlet.com/21297242/1oy1xajgy8z5/wish/204666205 21297242 https://padlet.com/21297242/1oy1xajgy8z5/wish/204666391 These are mountain valleys which have become hallowed out rock due to water erosion from small glaciers. These depressions often occur on the sides of mountains where snow and ice is able to accumulate and later erode off the sides. ]]> 2017-11-08 03:57:54 UTC https://padlet.com/21297242/1oy1xajgy8z5/wish/204666391 21297242 https://padlet.com/21297242/1oy1xajgy8z5/wish/204666573 These are formed from river valleys that have been filled with large glaciers. Through processes of abrasion by water flow, the glaciers deepen, straighten, and widen the valleys until the side valley has been cut off from the main valley below it. Waterfalls are often formed from this steep drop created due to the difference in the valley floors. These waterfalls later lead to more extensive erosion.]]> 2017-11-08 03:59:38 UTC https://padlet.com/21297242/1oy1xajgy8z5/wish/204666573 21297242 https://padlet.com/21297242/1oy1xajgy8z5/wish/204666715 Moraines are often formed by lateral movement on the sides of a glacier. As the glacier moves along the rough ground, it tears rock and soil up along its path. This material is then deposited on the glacier's edges, creating the streaks seen below. This process mainly occurs in matching ridges on either sides of a glacier. ]]> 2017-11-08 04:00:48 UTC https://padlet.com/21297242/1oy1xajgy8z5/wish/204666715 21297242 https://padlet.com/21297242/1oy1xajgy8z5/wish/204666824 This is a long process caused by a slow progression of rock and soil down a low grade slope. As sediments in the soil expand due to freezing or heating processes, they are lifted at right angles to the slope. Then, when they later shrink, the particles fall back down, thus moving at a downward angle. Creep often happens on slopes that contain loose, weathered material. And, eventually, this results in the tilting of trees, poles, fences, etc. The most contributing force that contributes to this process is frost heaving. This is the process described above, when water freezes, it forces the particles in the earth to be perpendicular to the slope and, when melting occurs, the particles are drawn directly downward by gravity.]]> 2017-11-08 04:01:56 UTC https://padlet.com/21297242/1oy1xajgy8z5/wish/204666824 21297242 https://padlet.com/21297242/1oy1xajgy8z5/wish/204666902 Many things can lead to this phenomenon, including soil erosion, earthquakes, and volcanic activity. These factors thus allow gravity to move rocks, soil, and/or debris down a slope, eroding away the earth below it.]]> 2017-11-08 04:02:49 UTC https://padlet.com/21297242/1oy1xajgy8z5/wish/204666902 21297242 https://padlet.com/21297242/1oy1xajgy8z5/wish/204667131 When masses of soil and fragmented rock rush down mountainsides due to water flow, they funnel into paths and channels and erode away objects in their path. This thus forms deposits on valley floors, as seen below. ]]> 2017-11-08 04:04:44 UTC https://padlet.com/21297242/1oy1xajgy8z5/wish/204667131 21297242 https://padlet.com/21297242/1oy1xajgy8z5/wish/204667262 Slumps form when a large masses of loose materials moves short distances down a slope, or slide along an upward or planar surface. The rock debris' movement downwards leads back-tilting of the top and slumped masses as earth removal occurs.]]> 2017-11-08 04:05:39 UTC https://padlet.com/21297242/1oy1xajgy8z5/wish/204667262 21297242 https://padlet.com/21297242/1oy1xajgy8z5/wish/204667393 When tectonic stresses and erosion occur, the granite rock fractures. These fractures develop parallel to the surface and lead to sheeting processes of the rock. This leads to the sliding/movement of granite debris downward, eventually leading to the accumulation of it at the bottom of large rock masses. When water enters the bedrock, ice wedging can also contribute due to the pressure it exhibits on unstable rocks.]]> 2017-11-08 04:06:54 UTC https://padlet.com/21297242/1oy1xajgy8z5/wish/204667393