Erosion And Weathering: Looking At Land (1976)

this Valley once supported a thriving agricultural Community now only the skeleton of the Town remains these buildings were full of life but now no one lives here and only the wind moves across the land from a distance the building seem to stand intact but a closer look shows signs of change the old hotel built of adobe bricks and wood still stands but it's slowly being worn away year after a year Wind and Rain cold and heat attack the structure these are the Agents of weathering the natural process by which material are broken down and taken apart roofs have collapsed and walls have crumbled these are signs of physical weathering a process by which materials are broken down into smaller and smaller pieces without their composition being changed these wagon wheels are evidence of the town's agricultural past but in time the wheels too will weather away the wood and iron are broken down by the process of chemical weathering in which the composition of materials is changed chemical weathering is causing this plow to rust as oxygen from rainwater combines with the iron in time the iron decomposes and returns to the Earth the process of weathering and erosion occur at the same time erosion is the wearing away and the movement of weathered materials from one place to another wind is an agent of erosion and moves small rock materials as easily as tumble weed this Gully which was washed out by water is now being filled with tumble weeds and weathered materials carried here by the wind the Gully was once a road that took people in and out of town but the wagon tracks are eroding and eventually all signs of the road will be gone Wind and Rain are also at work in the Town Cemetery Rippling the long grass and buffeting the tombstones perhaps the town's people hoped their monuments would last forever but the wood is weathering and the letters are so faded that they can hardly be read anymore even Stone monuments are wearing away in time there will be no clues that people once lived here the buildings and monuments are weathering and eroding the Adobe walls are returning to the Earth the same processes of weathering are changing this Boulder as time passes it too will disintegrate and return to the earth once it was part of this mountain but the Agents of weathering are wearing the mountain down reducing this mass of solid rock to Pieces large and small Boulders Pebbles and grains of sand at the same time the process of erosion carries these materials away a rock may set here for a hundred years and then loosened by the wind or rain tumble downhill pulled into the canyon by the force of gravity in this way the canyon slowly grows wider the River cuts the canyon deeper and removes Rock and soil that have been carried down by gravity over a short period of time the landscape doesn't appear to change because erosion here occurs over hundreds of thousands of years the most visible clue that erosion is taking place is the color of the river it is nearly the same color as the land as the river rushes along it eats away at the land running water is the most important agent of erosion for it transports much Earth material Downstream as it moves along the river widens and deepens the valley when the river slows the heavier materials are deposited the water also contains minerals which it has dissolved out of the rock the minerals are carried in solution so we cannot see them until they are deposited these Terraces have been built by the minerals that the river water has deposited so as the river flows it can build as well as erode The Terraces at Yellowstone National Park are built of minerals eroded from deep within the Earth and brought to the surface by Hot Springs hot water can hold more minerals in Solutions than cold water so when water from the hot spring cools at the surface it deposits relatively large quantities of a type of limestone called travertine Terraces like these May build in a few decades similar travertine formations are found underground in caves but here the building process is much much slower over many thousands of years groundwater has eroded the underground Limestone to form this Cavern now minerals carried in Solution by the groundwater are deposited as the water drips and splashes on the cavern floor but it can take hundreds or even thousands of years to build a single formation petrified wood is also formed by solution and deposition as groundwater seeps through a buried tree trunk it dissolves the wood and molecule by molecule replaces it with minerals for millions of years the Petrified Wood was buried deep beneath this desert but the softer sediments have eroded away revealing the logs this cap rock made of petrified wood protects the softer underlying material as this sediment erodes away the landscape is sculptured and the more resistant rocks and logs are left behind this cap Rock rests on a pillar of soil this rock rests on ice the ice is melting revealing rocks of all shapes and sizes the rocks are being carried along on the surface of a glacier in some places glaciers have been major agents of erosion they collect and carry enormous amounts of material grinding and shaping it as the ice erodes the land even extremely large Boulders can be carried many Kil mm on the ice you can think of a glacier as a slow moving River of ice as it flows down this Valley it reshapes the land it also widens and deepens the valley here is evidence of the power of glacial ice this rock has been scratched and scarred by rocks embedded in the Moon Glacier the landscape at Yus National Park was shaped by glaciers that move through and ground down the rock leaving behind this distinctive U-shaped valley the feature known as Half Dome has one flat side where erosion has removed much of the granite rock the eroded Rock was carried down the valley by the glacier today this landscape is no longer being changed by glaciers but periodic freezing and thawing weathers the rock erosion continues running water has tremendous power to change the landscape to erode it and to carry away materials in time almost all eroded materials are carried to the Sea one of the best places to see water at work is along an ocean Coast where powerful surf rolls in constantly pounding the shore the ocean is the final resting place of most of the Earth's sediments Pebbles sand and soil that are carried here by Rivers sediments are shifted about from place to place the water attacks the Pebbles washing over them again and again as the Rocks grind against each other they are gradually rounded and reduced in size erosion creates these rugged Coastal features the waves constantly pound the shoreline day after day year after year eroding the Rocks breaking them into smaller and smaller pieces es and carrying them along the shore eventually the surf can turn the irregular Rocky Coast into a smooth Sandy Beach the action of water reduces the rocks to Tiny grains of sand then washes them along the shore building a Beach water is the major force that is leveling the Earth's surface through erosion and and deposition wind does the same work eroding transporting and depositing settlements wind May pick up tiny Rock particles and carry them through the air for great distances when the wind speed is reduced the sand particles are deposited as sediment this is how sand dunes are built a dune is simply a pile of wind deposited sand it seems permanent solid and still but look closer the wind is at work Shifting the tiny grains of sand from place to place rearranging the Dune at the same time it creates it the sand continues to build up in some places hundreds of meters thick after millions of years the buried sand may turn into sandstone as the Sandstone is eroded the landscape changes again wind and water hollow out the Rock millions of years can pass the hollow in the rock may become a natural bridge in time only a remnant of the bridge remains an arch towering above the eroded landscape and eventually even the arch will be worn away all Landscapes are changing and can be explained in terms of erosion and deposition we cannot see most changes taking place because they occur too slowly but we can reconstruct what happened in the past by observing and interpreting the Rocks this is a long wall of volcanic rock called a dyke once it was below a mountain created by a volcano weathering and erosion slowly removed the mountain and Stripped Away Great layers of rock exposing the Dyke this explanation provides meaning for these Rock [Music] Pinnacles we recognize them as the eroded source of an ancient volcano stripped bare of its outer layers [Music] the base of this volcano is still hidden but in time it will be revealed long before this happens the town will be gone meanwhile the geologic processes of weathering and erosion will continue creating the Landscapes of the future e