Weathering, Erosion, Deposition

• Weathering is the breakdown of rock into sediments
• Physical/mechanical weathering (disintegration) changes only the side and shape of material, NOT composition.
• Frost/ice wedging (frost action) is a type of physical weathering in which water gets into cracks, freezes and expands, melts, more water gets in, freezes and expands, etc. until the rock breaks. This is common in New York and causes potholes
• Wind abrasion ("sandblasting") occurs when rocks have flat/angular surfaces, cuts, or grooves ("ventifacts")
• Abrasion by moving water such as rivers, streams, and ocean waves weathers rocks by breaking off small pieces/"corners" over time as rocks rub or bounce against each other. The sediments become smaller, and rounded/smoothed.
• Glaciers (ice) abrasion weathers rocks by scraping the rocks below. After the abrasion, the rocks have striations (grooves) following the direction of ice flow.
• Abrasion is a type of physical weathering
• Organisms physically weather material because plants roots can grow in cracks and pry rocks apart, and animals can break rocks apart by digging.
• Exfoliation (jointing) is a type of physical weathering in which overlying layers of rock are removed, pressure is released, rocks below expand and break along curved joints (parallel to surface), and peel off like layers of an onion. Exfoliation can also result from expansion and contraction due to temperature changes
• Chemical weathering (decomposition) is when chemical reactions change the composition of rock, and forms new substances
• Oxidation is a type of chemical weathering in which oxygen reacts with minerals in rock. (ex. iron + oxygen = iron oxide (rust))
• Hydrocolysis is a type of chemical weathering in which minerals and rocks are chemically broken down when combined with water (ex. feldspar + water = salts of calcium, potassium, and sodium dissolved in water + clay minerals
• Carbonation is a type of chemical weathering in which carbon dioxide dissolved in water produces carbonic acid, which reacts with and dissolves some rocks and minerals. Limestone and marble are most susceptible because they are calcite-based. Carbonation can cause sinkholes and caverns
• Organisms can chemically weather material because of acids formed by lichens (fungi and algae)the decay of dead organisms can dissolve rock
• Under normal conditions, weathering is slow, but rate is affected by mineral composition, climate, and surface area
• Mineral composition can affect weathering rate. The harder the mineral (ex. quartz-based), the more resistant it is to weathering (slower weathering rate). The softer the mineral (ex. calcite-based), the less resistant it is to weathering (faster weathering rate).
• Climate can affect weathering rate. In arid (dry) climates, their is slow, mostly physical weathering, such as wind abrasion. In cold and wet climates, there is faster, mostly physical weathering, such as frost action. In warm and wet climates, there is faster, mostly chemical weathering (sped up by temperature)
• Surface area can affect weathering rate. Smaller pieces have more surface area (than a larger piece with the same total volume) causing faster weathering
• Soil is a mixture of rocks (minerals), and air, water, and organic matter. It is generally made of 25% air, 25% water, 5% organic matter, and 45% mineral.
• Rocks weather, eventually becoming soil
• Humus (horizon O) is the top layer of soil. It is organic material in soil, which comes from decaying organisms, mostly leaves, twigs, and animal remains and wastes.
• Topsoil (horizon A) is the second layer of soil. It is loose soil, rich in organic material needed by plants, like humus and nitrogen. It contains most soil life
• Subsoil (horizon B) is the third layer of soil. It is rich in minerals like aluminum and iron. It contains humus and clays
• Parent material (horizon C) is the 4th and final layer of soil. It is mostly pieces of of weathered rock. The layers above it developed from this layer. The parent material determines the soil's pH
• Bedrock (horizon R) is below the parent material. It is a mass of rock, like granite, quartzite, limestone, or sandstone. It is not soil (located beneath horizon C)
• Residual soil is when the parent material is the local bedrock beneath the soil
• Transported soil is when the soil formed from parent material in a different area and was brought into a new area by wind, water, or ice (doesn't "match" the bedrock). Most soils in NY are transported soil because they were transported by a glacier.
• Climate affects soil formation. Arid climates have high mineral content and low organic matter because there are fewer plants. Humid climates have thick soils, low mineral content, and high organic matter because there are more plants.
• Organisms (decomposers) affect soil formation by adding nutrients and forming the topsoil
• Time affects soil formation because the longer the time of formation, the deeper the soil
• Once rocks are weathered, the sediments are eroded and deposited.
• Erosion is the transport of sediments
• Deposition is the dropping of sediments
• The main agents of erosion and deposition are gravity, wind, waves, and running water
• Gravity is the driving force behind most agents of erosion
• Sorting and shape of eroded sediments give evidence as to how/by which agent they were eroded and deposited.
• Sorted sediments are when larger, more dense, and rounded particles settle out first (on bottom). There are layers, and they're usually easy to see. Sorted sediments are associated with water and wind.
• Unsorted sediments are when sediments do not drop out in layers. They are all mixed up. Unsorted sediments are associated with gravity and ice.
• The topography (shape of land) depends on the balance between constructive processes (uplift/mountain building, deposition, lava flows, etc.) and destructive processes.
• Mass movements are the downhill transportation of rocks or sediment, caused directly by gravity. It is affected by slope, amount of water in soil, bedrock composition and structure. Sediments are angular and unsorted. They form the talus slope.