On the road of least resistance
Weathering and erosion slowly chisel, polish, and buff Earth's rock into ever evolving works of art—and then wash the remains into the sea.
The processes are definitively independent, but not exclusive. Weathering is the mechanical and chemical processses that break down and sculpts the rocks. Erosion transports the fragments away.
Working together they create and reveal marvels of nature from tumbling boulders high in the mountains to sandstone arches in the parched desert to polished cliffs braced against violent seas.
Water is nature's most versatile tool. For example, take rain on a frigid day. The water pools in cracks and crevices. Then, at night, the temperature drops and the water expands as it turns to ice, splitting the rock like a sledgehammer to a wedge. The next day, under the beating sun, the ice melts and trickles the cracked fragments away.
Repeated swings in temperature can also weaken and eventually fragment rock, which expands when hot and shrinks when cold. Such pulsing slowly turns stones in the arid desert to sand. Likewise, constant cycles from wet to dry will crumble clay.
Bits of sand are picked up and carried off by the wind, which can then blast the sides of nearby rocks, buffing and polishing them smooth. On the seashore, the action of waves chips away at cliffs and rakes the fragments back and forth into fine sand.
Plants and animals also take a heavy toll on Earth's hardened minerals. Lichens and mosses can squeeze into cracks and crevices, where they take root. As they grow, so do the cracks, eventually splitting into bits and pieces. Critters big and small trample, crush, and plow rocks as they scurry across the surface and burrow underground. Plants and animals also produce acids that mix with rainwater, a combination that eats away at rocks.
Rainwater also mixes with chemicals as it falls from the sky, forming an acidic concoction that dissolves rock. For example, acid rain dissolves limestone to form karst, a type of terrain filled with fissures, underground streams, and caves like the cenotes of Mexico's Yucatán Peninsula.
Back up on the mountains, snow and ice build up into glaciers that weigh on the rocks beneath and slowly push them downhill under the force of gravity. Together with advancing ice, the rocks carve out a path as the glacier slumps down the mountain. When the glacier begins to melt, it deposits its cargo of soil and rock, transporting the rocky debris toward the sea. Every year, rivers deposit millions of tons of sediment into the oceans.
Without the erosive forces of water, wind, and ice, rock debris would simply pile up where it forms and obscure from view nature's weathered sculptures. Although erosion is a natural process, abusive land-use practices such as deforestationand overgrazing can expedite erosion and strip the land of soils needed for food to grow.
CaCO3 and H2O
The solubility of limestone in water and weak acid solutions leads to karst landscapes, in which water erodes the limestone over thousands to millions of years. Most cave systems are through limestone bedrock. Since limestone is very pourous it is under extream subject to weathering and erosion.
Limestone often contains variable amounts of silica in the form of chert (chalcedony, flint, jasper, etc.) or siliceous skeletal fragment (sponge spicules, diatoms, radiolarians), and varying amounts of clay, silt and sand (terrestrialdetritus) carried in by rivers.
Some limestones do not consist of grains at all, and are formed completely by the chemical precipitation of calcite or aragonite, i.e. travertine. Secondary calcite may be deposited by supersaturated meteoric waters (groundwater that precipitates the material in caves). This produces speleothems, such as stalagmites and stalactites. Another form taken by calcite is oolitic limestone, which can be recognized by its granular (oolite) appearance.
The primary source of the calcite in limestone is most commonly marine organisms. Some of these organisms can construct mounds of rock known as reefs, building upon past generations. Below about 3,000 meters, water pressure and temperature conditions cause the dissolution of calcite to increase nonlinearly, so limestone typically does not form in deeper waters (see lysocline). Limestones may also form in lacustrine and evaporitedepositional environments.
Calcite can be dissolved or precipitated by groundwater, depending on several factors, including the water temperature, pH, and dissolved ionconcentrations. Calcite exhibits an unusual characteristic called retrograde solubility, in which it becomes less soluble in water as the temperature increases.
A Rolling stone Gathers no moss.
In the context of stream hydrology, sediment is inorganic and organic material that is transported by, suspended in, or deposited by streams. Sediment load, which is the quantity of sediment transported by a stream, is a function of stream discharge, soil and land-cover features, weather conditions, land-use activities, and many other factors. Sediment load carried by streams and rivers can be composed either of fine materials, mostly silts and clays, or larger materials such as sand.
Solid sediment load can be divided into two components on the basis of the mode of sediment transport: suspended sediment, and bedload sediment, each of which is produced by mechanical weathering processes, is clearly visible, and is able to settle out of water. Suspended sediment consists of silt-sized and clay-sized particles held in suspension by turbulence in flowing water. Bedload sediment consists of larger particles which slide, roll, or bounce along the streambed by the force of moving water. Dissolved load consists of inconspicuous material in solution moving downstream. It is produced by chemical weathering processes, and does not settle out of water.
Sediment yield is the total quantity of sediment transported from a watershed (drainage basin) at a given location in a given period of time. Low suspended sediment yields can be attributed to, among other factors, a region's low erosion rate. Permeable soils and low topographic relief, in general, help limit the availability of eroded material from within a watershed. Conversely, relatively impermeable soils and steep topography can yield high erosion rates and therefore greater sediment yield.
Did you know?
Each kind of sedimentary rock turns into a different kind of metamorphic rock - limestone turns into travertine or marble, and shale turns into slate, and sandstone turns into quartzite. Even though slate is a metamorphic rock, it still looks a lot like a sedimentary rock - it is still in thin layers.
Now that we learned a little bit about erosion and the effects it has on limestone, take a moment to study ground zero, as well as the placards for GZ. With the information above, and information at GZ you should be able to answer the following questions. You have 24 hours to send me an email (found in my geocaching profile) with the correct answers. Failure to do so will result in the removal of your "Found it log". Please add the GC code and title in the subject line. If you are sending answers for multiple people in your group, please add all the names in your email to ensure they don't have their log deleted :) Photos with you or in the group of the area would be greatly appreciated.
Requirements: (please do not put your answers in the log)
1 According to the Ground Zero Placard, Steams flow in the the watercourse of what?
2 What Process of erosion is going on under your feet?
3 Explain what has happend to the limestone at the "S" curve of this stream.
4 What man made device is allowing you to observe Sedimentary
5 Look at the limestone within the water, describe it's characteristics (without getting wet, but extra credit if you do).
6 What is the last four words above the number 36 on the placard at Ground Zero?
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