Romano - 223 What are the different ways rocks can be weathered? Weathering - the breakdown of rocks and minerals at the Earth s surface 1. 2. PHYSICAL WEATHERING Rock is broken into smaller pieces with NO change in its chemical composition CHEMICAL WEATHERING Rock is broken down by chemical reactions with air and water resulting in a change in chemical composition. a. ABRASION a wearing, grinding, or rubbing away of rock material by friction a. OXIDATION oxygen chemically unites with iron and water to form iron oxide (rust) b. THERMAL EXPANSION - heating and cooling causes rocks to expand and contract causing rock to crack b. CARBONATION - CO 2 dissolved in H 2 O makes carbonic acid which dissolves calcite-rich rocks. (limestone cave formation) c. FROST ACTION (ice wedging) - water repeatedly seeps into cracks, freezes, expands, and eventually splits rock c. HYDROLYSIS feldspar chemically unites with water to form clay d. ROOT ACTION (plant action, root pry) - plant s roots grow into cracks and break apart rock d. ACTION OF ACIDS - - organic acids - when plants and animals decay, they release acids which can dissolve rock - acid rain (from air pollution).
Romano - 224 CLIMATE chemical weathering occurs faster in warmer, wetter climates COMPOSITION harder rocks and minerals are more resistant to weathering and break down slower What factors affect the rate of weathering? PARTICLE SIZE smaller particles have more surface area exposed and weather faster PARTICLE SHAPE angular particles weather faster because they have more edges that are easier to break off
Romano - 229 GRAVITY a.k.a. mass movement the driving force behind all erosion - landslides - mudslides - avalanches (unsorted sediments at the bottom of a steep slope) RUNNING WATER the dominant type of erosion on Earth Evidence: rounded, smooth, sorted sediments (separated by size) What are the different agents of erosion? the movement of weathered material WIND dominant in dry regions (deserts) Evidence: frosted, sorted sediments dune formation and migration wind blows sand up sand builds up, then slides down dune moves GLACIERS large masses of moving ice Evidence: scratched, polished bedrock (grooves / striations) hills of unsorted sediments U-shaped valleys
Romano - 230 How do streams cause erosion? 1. Gradient The steeper the gradient, the faster the velocity of a stream. 2. Stream Discharge ( or volume of the water in the stream) The greater the discharge, the faster the velocity. Discharge is greatest in the spring when snowcaps on mountains melt and stream channels fill with melt-water. 3. Channel Shape The straighter the stream channel, the faster the velocity. (abrasion at curves causes stream to slow down.) The greater the stream velocity, the greater the stream s carrying power. Faster streams can carry more particles, and larger particles. **Use the chart to determine the minimum velocity necessary to carry specific particle sizes.** 1. Rolling Larger, denser particles bounce and roll along streambed. 2. Suspension Finer particles are carried along in the water. 3. Solution Some minerals dissolve and become ions in the water (salt).
Romano - 232 What are the stages in the development of a stream? Straight and narrow channels Steep slopes Waterfalls and rapids V-shaped valleys (down-cutting dominant) Some meanders (curves) Slopes less steep Development of a floodplain (flat area surrounding stream that gets covered with water during flood stage) Many meanders Much flatter terrain Large floodplain Wider channels (side-cutting dominant) Oxbow lakes (horseshoe-shaped cut-offs of stream channel)
Romano - 233 Weathering, Erosion, and Deposition How does the shape of a stream change over time? Water moves faster on the outside curve causing more erosion. On the inside curve water moves slower depositing (dropping off) sediments. B and E are outside curves water moves faster causing more erosion. A and F are inside curves water slows down and sediment is deposited. point bars mini-beaches formed by deposition on the inside curve of a stream where the current slows down
Romano - 234 STREAM VELOCITY As a stream slows down, more sediments are deposited PARTICLE SIZE The larger the particle size, the faster the rate of deposition What factors affect the rate of deposition by a stream? the dropping off of sediments how fast a particle settles (cm/sec) how long it takes for a particle to settle (seconds) PARTICLE DENSITY The more dense the particle, the faster the rate of deposition PARTICLE SHAPE The flatter the particle, the slower the rate of deposition
Romano - 235 What are the different depositional sorting patterns? particles get naturally the separated natural separation by size, of density, sediments and/or shape based on size, shape and density VERTICAL SORTING - occurs when there is a sudden depositional event in water - larger particles fall first, followed by smaller ones on top LAYERING or GRADED BEDDING indicates multiple depositional events HORIZONTAL SORTING When a stream enters a body of still water (lake or ocean) it loses kinetic energy (slows down) dropping off bigger particles right at the mouth (end of stream). Smaller particles are carried farther into the still water. Leads to formation of a delta (triangular depositional feature at the mouth of a stream). stream flow still water pebbles sand silt clay
Romano 235A What are the different parts of a stream system? 1. Watershed - A watershed is the area of land that catches rain and snow and drains into streams, rivers, lakes, and groundwater. Since rivers are connected, problems in one place of the watershed can affect other places in the watershed even hundreds of miles away. 2. Tributaries - rivers and streams that feed into a larger one 3. Delta - A delta is a triangular-shaped depositional feature formed at the mouth (end) of a stream. Deltas form when a stream slows down upon entering the ocean and sediment gets dropped off and accumulates over time.
Romano 235B How does wave erosion / deposition affect coastal areas? sand accumulation sand deprivation Longshore Drift movement of sand parallel to the shoreline as waves strike the beach at an angle Jetties and Groins man-made walls built perpendicular to the beach to try and slow the effects of longshore drift change the coastal landscape by preventing sand from moving down shore C sandbars waves pull sand away from the shoreline and builds up under water barrier island forms when a when a sandbar accumulates enough sand to rise above sea level (Jones Beach Island, Fire Island)
Romano - 238 1. Glacier Profile When accumulation is greater than melting, a glacier advances. When melting is greater than accumulation, a glacier retreats (appears to move backwards). As glaciers move across the land, boulders carried by glaciers scratch the bedrock leaving parallel grooves (striations) that indicate direction of glacier movement. erratics random boulders dropped by the glacier snow accumulation How does glacial erosion/deposition affect landscapes? melting 2. Glacier Cross-Section U-shaped valley Middle of glacier moves faster than sides as shown by experiments with surface markers
Romano - 239 3. Glacially-Formed Landscape Features a. Moraines - elongated hills of glacial till (unsorted deposits) dropped off directly by glacier when it melts (hills on Long Island s north shore) b. Drumlins - unsorted teardrop-shaped hills that point in direction of glacier movement c. Kettle Lakes steep lake left when glacier carves out a hole and then ice from glacier melts to fill it (N.Y. s Finger Lakes) d. Outwash Plain sorted rock material deposited by glacial meltwater (Long Island s flat south shore)