IBL - Forces that Change the Geosphere Lesson

 

Forces that Change the Geosphere

Despite our tendency to consider Earth as static, it is actually a dynamic and ever-changing planet. Wind, water, and land erode and shape the geosphere which can affect all other spheres. Throughout earth's history several things have changed the face of the Earth including but not limited to volcanoes, glaciers, earthquakes, erosion, wind, etc.

Erosion

Wind, water, and ice are the three agents of erosion, or the carrying away of rock, sediment, and soil. Erosion is distinguished from weathering — the physical or chemical breakdown of the minerals in rock. However, weathering and erosion can happen simultaneously. Erosion is a natural process, though it is often increased by humans' use of the land. Deforestation, overgrazing, construction, and road building often expose soil and sediments and lead to increased erosion. Excessive erosion leads to loss of soil, ecosystem damage, and a buildup of sediments in water sources. Building terraces and planting trees can help reduce erosion.

Glaciers

In the Arctic and sub-Arctic, glacial erosion has shaped much of the landscape. Glaciers primarily erode through plucking and abrasion. Plucking occurs as a glacier flows over bedrock, softening and lifting blocks of rock that are brought into the ice. The intense pressure at the base of the glacier causes some of the ice to melt, forming a thin layer of subglacial water. This water flows into cracks in the bedrock. As the water refreezes, the ice acts as a lever loosening the rock by lifting it. The fractured rock is thus incorporated into the glacier's load and is carried along as the glacier slowly moves. Abrasion happens when the glacier's ice and rock fragments act as sandpaper, crushing the rock into finely ground rock flour and smoothing the rock below. Meltwater streams of many glaciers are grayish in color due to high amounts of rock flour.

Coastal erosion has become a major issue in recent years in the Arctic, with Alaska's North Slope losing as much as 30 meters (100 feet) per year! Climate change is thought to be the underlying cause. As the climate warms and sea ice melts, more of the sun's energy is absorbed by ocean water. As this heat is transferred to the land, the permafrost (frozen soil) thaws, making the coast vulnerable to erosion from wave action and storms (which are more frequent due to warmer temperatures and open water).

This documentary short shows how rapidly The Glaciers in Glacier National Park are shrinking. Historic photography and time-lapse video supports informative narration that describes how all of the park's glaciers will disappear perhaps in the next decade.

Watch the video:

Wind

Wind is also an agent of erosion. It can carry dust, sand, and volcanic ash from one area to another. The force of wind can blow sand into towering dunes (as seen in the Gobi desert), or blast sand against rock with such force wearing the rock away (as seen in the Arches National Park).

Wind can also erode material until nothing remains at all. Over millions of years, wind and water eroded an entire mountain range in central Australia. Uluru, also known as Ayers Rock, is the only remnant of those mountains.

Plate Tectonics

The theory of plate tectonics describes the motions of earth's geosphere, or outermost layer of hard, solid rock over geologic time. Plate tectonics provide scientists with a great deal of information about an area's past. The Earth is broken down into seven major and many minor tectonic plates. These plates move in relation to each other, slowly changing the location of earth's continents and oceans. Geological evidence from Antarctica supports the theory that North America and Antarctica were connected approximately one billion years ago in the global supercontinent Rodinia. The continents eventually broke apart, merging again approximately 200 million years ago in the supercontinent Pangaea. Fossil evidence from this time period confirms that Antarctica was connected to Australia and South America and much warmer than it is today. The movement of the tectonic plates also means that they are associated with much of the world's volcanic and seismic activity.

Volcanoes

A volcano is simply an area where magma, or molten rock, from the earth's mantle reaches the earth's surface, becoming lava. Most volcanoes occur at plate boundaries, where two plates are moving away (diverging) or together (converging). A few volcanoes like the Hawaiian Islands form from a hot spot, or a weak spot in earth's crust, where magma forces its way to the surface. Volcanic eruptions may be explosive (violent) or effusive (passive), depending on the lava chemistry (amounts of silica and dissolved gases). Silica is a mineral found in nature as sand or quartz. High levels of silica mean very viscous (thick) lava, and low levels mean more fluid lava. Dissolved gases build up inside the volcano, much like a can of soda or other carbonated beverage. The higher the level of gas, the more pressure that builds - and the more violent an explosion. The combination of silica and dissolved gas levels determines the type of eruption and shape of the volcano.

Earthquakes

Seismic activity (earthquakes) is most often associated with tectonic plate boundaries. As plates slowly move, their jagged edges stick and suddenly slip, causing an earthquake. Earth quakes can cause ground motion and displacement, damage to buildings, and quake-caused fires, landslides, and seismic sea waves (tsunamis) all of which can change the Earth's landscape.

 

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