Exam 4 Review and Terms PDF

Preview

Summary

Download Exam 4 Review and Terms PDF

Description

E XAM R EVIEW – U NIT 4 River channel: The bottom of a valley and the outline or border of a river; types include braided streams (high sediment load, high velocity) and meanders (low sediment load, low velocity). River valley: Encompass the entire area between the tops of the slopes on both sides of the river or stream. The cross-sectional profile of many river valleys is v-shaped, but many other valleys have a broad, low profile. Floodplain: A stream channel migrating over the floor of a valley; flat area in valley level with top of channel. In broad valleys, a floodplain can lie on either side of the channel. Erosional floodplains can form when a stream erodes bedrock or unconsolidated sediment as it migrates. Successive floods build up natural levees. Mountains streams: Streams are narrow and have steep walls, and the channel may occupy most or all of the valley bottom. Braided streams: Channel divides into a network of channels then rejoins to form a pattern that looks like braids of hair. Tend to form in rivers with large variations in volume of flow combined with a high sediment load and easily erodible banks. They do not form oxbow bonds. Meandering rivers: Floodplains or channels that have curves and bends. Usual in streams flowing on low slopes in plains or lowlands. They are less pronounced but still common where the channel flows on higher slopes and harder bedrock. In such terrain, meandering stretches may alternate with long, relatively straight ones and can create oxbow lakes and have point bars. Levees: Ridges of coarse material that confine the stream within its banks between floods, even when water levels are high. Where natural levees have reached a height of several meters and the stream almost fills the channel, the floodplain level is below the stream level. Cut banks: The outside bank of a water channel (stream), which is continually undergoing erosion, they are shaped like a cliff and are opposite of the point bar. Velocity of floodwaters: If floodwaters spread out the velocity of the water slows down and the current loses the ability to carry sediments. The floodwater velocity drops most quickly along the immediate borders of the channel. As a result, the current deposits much coarse sediment, typically sand and gravel, along a narrow strip at the edge of the channel. Drainage networks: Drainage divides force water to run down one side of the rise. Every topographic rise between two streams, despite its size, forms a divide – a ridge of high ground along which all rainfall runs off down one side of the rise or the other. A drainage basin is an area of land, bounded by divides, that funnels all its water into the network of streams draining the area; may be a small area, such as a ravine surrounding a small stream, or a great region drained by a major river and its tributaries. A continent has several major drainage basins separated by major divides. 1

The different drainage patterns are: (1) Dendritic drainage which is characterized by branches similar to branches on a tree, typical of terrains where the bedrock is uniform, such as horizontally bedded sedimentary rocks or massive igneous or metamorphic rocks. (2) Rectangular drainage is developed on a strongly jointed rocky terrain that tends to follow the joint pattern. (3) Trellis drainage develops in valley and ridge terrain, where rocks of varying resistance to erosion are folded into anticlines and synclines. (4) Radial drainage patterns develop on a single large peak, such as a large dormant volcano. River erosion of solid rock: Abrasion (sand and pebbles carried by the river slowly wear the rock out the rock out), headward erosion (process in which rivers cut upstream, rather than downstream, and usually widens and deepens the valley), physical weathering (impact of objects against the rock), chemical weathering (changes in a rock’s minerals and weakens it along joints and cracks), and gullies (landform created by running water, eroding sharply into soil, typically on a hillside). Laminar flow of water: The simplest kind of movement, straight or gently curved streamlines run parallel to one another without mixing or crossing between layers; affected by factors such as velocity, depth, and viscosity. Turbulent flow of water: A more complex pattern of movement, in which streamlines mix, cross, and form swirls and eddies. Fast-moving river waters typically show this kind of motion and they are affected by factors such as velocity, depth, and viscosity. Saltation: Sand grains in a flow typically move by an intermittent jumping motion along the streambed. The grains are sucked up into the flow by turbulent eddies, move with the current for a short distance, and then fall back to the bottom. Stream capacity: The total sediment load carried by a flow. The velocity and the volume of a flow affect both the competence and the capacity of a stream. Stream competence: A flow’s ability to carry material of a given size. As a current increases in velocity and coarser particles are suspended, the suspended load grows. The velocity and the volume of a flow affect both the competence and the capacity of a stream. Evaporation: Requires a lot of energy, so factors that affect evaporation like soil moisture, vegetation, and subsurface flow of water are very important. The cyclical movement of water – from the ocean to the atmosphere by evaporation, to the surface through rain, to streams through runoff and groundwater, and back to the ocean – is the hydrologic cycle. Transpiration: Release of water vapor from plants, and is a component of the hydrologic cycle. Sublimation: When a solid becomes a gas by skipping the liquid stage. Runoff–precipitation relationship: When levels of precipitation and runoff are measured over a large area (such as all the states drained by a major river) and over a long period, the relationship is less extreme but still strong. Stronger in local areas but weaker in regional areas.

2

Precipitation in arid areas: Rarely rains so water is a precious resource. Much of the precipitation is lost by evaporation and infiltration and only a small fraction of precipitation ends up as runoff. Rock porosity: Tells us how much water a rock can hold; higher in soils, sediments, and sedimentary rocks (10 to 40%) than in igneous or metamorphic rocks, where porosity is created mostly by fractures, including joints and cleavage planes. It depends on the size and shape of the grains that make up soils and siliciclastic sedimentary rocks and on how they are packed together. Rock permeability: Ability for fluids (gas or liquid) to flow through rocks. High permeability means that fluids can move rapidly but the permeability is affected by the pressure of the rock. Aquiclude: An aquifer that is that has a relatively impermeable bed; groundwater either cannot flow through them or flows through them very slowly. When aquicludes lie both over and under an aquifer, they form a confined aquifer. Artesian well: Wells that are in a confined aquifer where the elevation of the ground surface is lower than that of the water table in the recharge area. They are desirable because the pressure brings the water to the surface. At any point in the aquifer, the pressure is equivalent to the weight of all the water in the aquifer above that point. Aquifer: Beds that store and transmit groundwater. Unconfined aquifers, impermeable aquifers that have water traveling through beds of more or less uniform permeability that extend to the surface in both discharge and recharge areas. The level of the reservoir for the unconfined aquifer is the same as the height of the water table. Permeable aquifers are bounded above and below by low-permeability beds. Abundance of gases in the atmosphere: Atmospheric composition is 78% nitrogen, 21% oxygen, and 1% other gases (argon, carbon dioxide, water vapor, ozone, methane, etc.) Water vapor concentrated near Earth’s surface; it and carbon dioxide are the principal greenhouse gases. If there were no greenhouse gases, heat generated by solar radiation would pass out easily through the atmosphere, and Earth’s climate would be much colder. Cryosphere: The ice component of the climate system, comprises 33 million cubic km of ice, primarily in the ice caps and glaciers of the Polar Regions. Today continental glaciers and ice sheets cover 10% of the land surface (15 million square km), storing about 75% of the world’s fresh water. The sea ice covers 14-16 million square km during winter in the Arctic Ocean and 17-20 million square km of the Southern Ocean around Antarctica. About 33% of the land surface is covered by seasonal snows; only 2% is not covered in the Northern Hemisphere. Floating ice includes sea ice and frozen lake and river water. The seasonal exchange of water between the cryosphere and hydrosphere is an important process of the climate system. Melting snow is the source of much of the fresh water in the hydrosphere. Lithosphere impact on climate: Important factor of the lithosphere is the land surface which makes up 30% of Earth’s total area and affects how solar energy is absorbed and returned to the atmosphere. This can affect the fresh water on earth due to evaporation. As the temperature rises, the land radiates more energy as infrared waves back into the atmosphere and more water evaporates from the land surface. 3

Evaporation requires considerable energy, so soil moisture and other factors that influence evaporation – such as vegetation and the subsurface flow of water – are very important in controlling surface temperatures. Albedo: The reflection of solar energy back into space. A rise in temperature reduces the accumulation of ice and snow in the cryosphere, which decreases Earth’s albedo and increases the energy its surface absorbs. The increased warming of the atmosphere enhances the temperature rise – another example of positive feedback. Greenhouse gas effect: Gases such as water vapor, carbon dioxide, and ozone absorb solar energy coming directly from the Sun or reflected from Earth’s surface and reradiate it as infrared energy in all directions, including downward to the surface. The net effect is to trap heat within the atmosphere by increasing the temperature of the surface relative to the temperature at higher levels of the atmosphere. Relative humidity: The amount of water vapor in the air, expressed as a percentage of the total amount of water the air could hold at that temperature if saturated. Warm air can hold more vapor than cold air: When unsaturated warm air at a given relative humidity cools enough, it becomes supersaturated and some of the vapor condenses into water droplets which form clouds. Latitudinal variation in rainfall: Variations in precipitation patterns control weathering and erosion rates, which influence rates of tectonic uplift. Mountain ranges can form rain shadows, areas of low rainfall on their leeward (downwind) slopes. Thermohaline circulation: Differences in temperature and salinity. On a planetary scale, the thermohaline circulation acts like a conveyor belt running through the oceans that moves heat from the equatorial regions toward the pole. Changes to it can impact global climate. Ozone in the atmosphere: Another minor constituent of the atmosphere is ozone (O3+), a highly reactive gas produced primarily by the ionization of oxygen by ultraviolet radiation from the Sun. In the lower part of the atmosphere, ozone exists in only tiny amounts although it is a strong enough greenhouse gas to play a significant role in the atmospheric heat budget. Oxygen isotope variations between glacials and inter-glacials: A precise record of glacial movements can be obtained by measuring the proportion of two oxygen isotopes preserved in oceanic sediments. The lighter and more common isotope, oxygen-16, has a greater tendency to evaporate from the ocean surface than the heavier oxygen-18. Therefore, during glaciations, marine sediments become enriched in oxygen-18, because oxygen-16 is preferentially evaporated from the oceans and trapped in glacial ice. The “Little Ice Age”: Period between about 1300 and 1870 during which Europe and North America were subjected to much colder winters than during the 20th century. The period can be divided in two phases, the first beginning around 1300 and continuing until the late 1400s.

4...