Earth's Climatic Regions PDF

EARTH’S CLIMATIC REGIONS GES 2613 Topic 9 – 10/02/24  QUESTIONS FOR TODAY What is climate and how is it classified? What are the distinguishing factors of our main climatic regions?  CLIMATOLOGY Climate is the average condi...

EARTH’S CLIMATIC REGIONS GES 2613 Topic 9 – 10/02/24  QUESTIONS FOR TODAY What is climate and how is it classified? What are the distinguishing factors of our main climatic regions?  CLIMATOLOGY Climate is the average condition of weather over many years This average condition can still differ over time, which is called climate change Climatology is the study of climate and its variability, including long-term weather patterns and causal factors  CLIMATIC REGION Even though no two places have the same climate, we can group places into climatic regions based on overall similarities Climate is generally classified based on temperature and precipitation since they integrate pressure, lifting mechanisms, air masses, and energy availability  CLASSIFICATIONS Classification is the grouping of things into categories based on general similarities Climate classifications are based on an empirical approach that uses real world data  CLIMATE CLASSIFICATIONS The boundaries of climate regions are transition zones or areas of gradual change Climate can be classified into six main categories: Tropical – tropical latitudes with no winter Mesothermal – midlatitudes with mild winters Microthermal – mid/high latitudes with cold winters Polar – high latitudes Highland – high elevation at all latitudes Dry – permanent moisture deficit at all latitudes CLIMATE CLASSIFICATIONS  TROPICAL CLIMATES Tropical climates are the most extensive as they occupy ~36% of Earth’s total surface Located around the equator between ~20°N/S Winterless climates produced by consistent insolation and subcategories determined by the dominance of the ITCZ  TROPICAL CLIMATES – TROPICAL RAIN FOREST Tropical rainforest climates are constantly moist and warm because the ITCZ is present all year Notable water surpluses power some of the world’s greatest rivers (e.g., Amazon, Congo Rivers) Dense tree canopy created Amazon by evergreen broadleaf trees Rainforest TROPICAL CLIMATES – TROPICAL RAIN FOREST Amazon Rainforest  TROPICAL CLIMATES – TROPICAL MONSOON Tropical monsoon climates feature a dry season that lasts ~1 month or longer The wet season lasts for ~6 months or more since this is when the ITCZ is present Often located along the coast, since the climate is also influenced by seasonal variations in wind Yangon, Myanmar  TROPICAL CLIMATES – TROPICAL SAVANNA Tropical savanna climates have a pronounced dry season when a water budget deficit develops The wet season lasts for ~6 months or less since the ITCZ is present for a shorter duration Land cover consists of grasslands and scattered Serengeti, trees Tanzania TROPICAL CLIMATES – TROPICAL SAVANNA Serengeti, Tanzania  MESOTHERMAL CLIMATES Mesothermal climates describe warm and temperate climates where true seasonality begins Highly variable weather since these climates are where air mass interactions are most common  MESOTHERMAL CLIMATES – HUMID SUBTROPICAL HOT SUMMER Influenced during the summer by mT air masses that enable convective showers In the fall, winter, and spring midlatitude cyclones produce precipitation These two mechanisms together provide steady precipitation year round Columbia, South Carolina  MESOTHERMAL CLIMATES – HUMID SUBTROPICAL DRY WINTER Influenced by the winter dry phase of the monsoon Have a summer month that receives ~10x more precipitation than the driest winter month Typically located poleward of tropical savanna climate Chengdu, China  MESOTHERMAL CLIMATES – MARINE WEST COAST Marine west coast climates feature mild winters and cool summers, particularly for their latitudes, due to the moderating influence of water Regions are dominated by mP air masses so severe weather is less common Dunedin, New Zealand  MESOTHERMAL CLIMATES – MEDITERRANEAN Receive at least 70% of their annual precipitation during the winter months because summer months are dominated by subtropical high pressure A water balance deficit develops during the summer San Francisco  MICROTHERMAL CLIMATES Microthermal climates are cool to cold and occur poleward of mesothermal climates Located primarily in the Northern Hemisphere due to lack of sizable land masses in the Southern Hemisphere More extreme seasonality  MICROTHERMAL CLIMATES – HUMID CONTINENTAL HOT Humid continental hot summer climates have the warmest summer temperatures within the microthermal class In the summer, mT air masses influence precipitation Pervasive climate type in the Midwest New York City  MICROTHERMAL CLIMATES – HUMID CONTINENTAL MILD Humid continental mild summer climates are slightly cooler and located farther toward the poles Overall, precipitation is lower but snowfall is much heavier and important to soil-moisture recharge Moscow  MICROTHERMAL CLIMATES – SUBARCTIC COOL SUMMER Subarctic cool summer climates cover vast stretches of Canada, Alaska and Russia Precipitation is low but so is potential evapotranspiration, so soils are generally moist and support forests Average monthly temperatures are below freezing for ~7 months Churchill, Manitoba  MICROTHERMAL CLIMATES – SUBARCTIC COLD WINTER Subarctic cold winter climates occur only in Russia The extreme continentality contributes to some of the largest annual temperature ranges on Earth, which can exceed 100°F Verkhoyansk, Russia  POLAR AND HIGHLAND CLIMATES Polar and highland climates experience no true summer Temperatures are too cold to allow for tree growth Low sun altitude throughout the year or high elevation responsible for the cold temperatures Low precipitation so the regions are frozen deserts  POLAR AND HIGHLAND CLIMATES – TUNDRA Land is under snow cover for 8 – 10 months This severely restricts plant growth Some tundra climates have a strong marine influence that moderate temperature extremes  POLAR AND HIGHLAND CLIMATES – ICE CAP AND ICE SHEET An ice sheet is a continuous layer of ice covering an extensive continental region (i.e., Antarctica and Greenland) Ice caps cover a smaller area Monthly average temperatures always below freezing, and climate is dominated by dry, frigid air masses  DRY CLIMATES Water demand exceeds precipitation creating permanent water deficits The degree of the deficit helps differentiate between deserts (bigger deficit) and steppes (smaller deficit) Dominated by subtropical high-pressure systems or rain shadows  DRY CLIMATES – TROPICAL/ SUBTROPICAL HOT DESERT Annual average temperatures above 65°F Some regions receive virtually no rainfall while others receive up to 14 inches Summer temperatures regularly exceed 120°F for certain locations Riyadh, Saudi Arabia  DRY CLIMATES – MIDLATITUDE COLD DESERT Located in portions of the American Southwest Because of the lower temperatures and reduced water demand, rainfall must be low – in the realm of 6 inches – to be classified as a midlatitude cold desert Albuquerque  DRY CLIMATES – TROPICAL/ SUBTROPICAL HOT STEPPE Typically located around the edges of hot deserts Subtropical high not quite as dominate so precipitation can approach 24 inches Walgett, Australia  DRY CLIMATES – MIDLATITUDE COLD STEPPE Typically occur poleward of 30° N/S and of the midlatitude cold desert climate types Rainfall is sporadic and can range from 8 inches to 15 inches Predominant climate type of the Great Plains in North America Lethbridge, Alberta WATER RESOURCES GES 2613 Topic 8 – 09/30/24  QUESTIONS FOR TODAY Where did the water on Earth come from and how is it distributed? How does the hydrologic cycle work? What is a water budget and how is it calculated? How are the surface and ground water resources managed?  HYDROLOGY Hydrology is the scientific study of water including its global circulation, distribution and properties with an emphasis on water at and below Earth’s surface In the solar system, Earth is the only planet with significant quantities of water as it covers 71% of its area  WATER ON EARTH Much of Earth’s water originated from its interior It escapes via outgassing where water and water vapor emerge from below the surface as a gas Still occurs today at geysers and during volcanic eruptions  DISTRIBUTION OF WATER 97.2% of water resides in oceans The remaining 2.8% is freshwater Ice sheets and glaciers contain the greatest amount of freshwater Surface water represents less than 1% of freshwater  HYDROLOGIC CYCLE Circulation of water between the atmosphere, hydrosphere, biosphere and lithosphere Can be divided into three main components: Atmosphere (residency time of ~10 days and fastest portion of the cycle) Surface Subsurface  HYDROLOGIC CYCLE – ATMOSPHERE Atmospheric Inputs: Evaporation – 86% occurs over oceans Transpiration – plants releasing water vapor from their leaves Atmospheric Outputs: Precipitation – 78% occurs over oceans  HYDROLOGIC CYCLE – SURFACE Pathways for precipitation as it reaches the surface: Interception – precipitation lands on vegetation prior to reaching the ground Throughfall – precipitation that reaches the ground Pathways for precipitation once on the surface: Infiltration – water that soaks into the subsurface Overland flow – water that flows across the surface due to saturation or imperviousness  HYDROLOGIC CYCLE – SURFACE Two primary surface outputs: Evapotranspiration – combination of evaporation and transpiration Percolation – slow passage of water through porous soil to groundwater  HYDROLOGIC CYCLE – SUBSURFACE Water reaches the subsurface Comal Springs at Landa Park through infiltration and then further percolation Most subsurface water returns to the atmosphere by evaporation from the soil or transpiration Groundwater can also leave the subsurface by intersecting a stream channel or in the form of springs  WATER BUDGETS A water budget is derived by measuring the water inputs, outputs, and storage for a given location and time Important for water resources management - - =  WATER BUDGETS Precipitation, in all its forms, is what supplies moisture to Earth’s surface It is often measured using tipping bucket rain gauges Spatial patterns of precipitation mirror location of lifting mechanisms and certain air mass types  WATER BUDGETS The moisture demand is determined by actual evapotranspiration (AET) into the atmosphere Potential Evapotranspiration (PET) is the amount of evapotranspiration that would occur if moisture was unlimited If PET > AET, water demand must be met by moisture storage Evapotranspiration can be measured using a lysimeter  WATER BUDGETS Water can be stored in soil-moisture storage Soil moisture recharge – filling up the soil moisture storage Soil moisture utilization – soil moisture used to meet water demand Capillary water is what is available to meet demand  WATER BUDGETS If all expenditure demands are met, there is a surplus that often becomes runoff and feeds streams/lakes and replenishes ground water If precipitation and soil moisture do not meet demand, there is a deficit that can cause drought conditions  SURFACE WATER RESOURCES The largest amount of surface freshwater on Earth is locked in glaciers and polar ice The seasonal melting of glaciers and snowpack feeds streamflow and helps enhance water supply  SURFACE WATER RESOURCES Surface runoff and baseflow from groundwater move across Earth’s surface in rivers and streams Lake Baikal in Russia is the largest lake in the world by volume  SURFACE WATER RESOURCES Reservoirs, human made Olmos Dam – Built after the devastating flood in 1921 lakes by dams, are often used for hydroelectric power and water storage 2015 – Hydro accounted for 6% of power generation in the US Flood control is another purpose of building dams  GROUNDWATER RESOURCES Groundwater lies beneath the surface and can accumulate over long periods of time as water percolates down through the soil An aquifer is a subsurface layer of permeable rock through which groundwater can flow in amounts adequate for wells and springs  GROUNDWATER RESOURCES Unconfined Aquifer: has a permeable layer above it which allows water to pass through Confined Aquifer: has impermeable layers above and below so it is pressurized EDWARDS AQUIFER  EDWARDS AQUIFER Contributing Zone: rolling area Goat Cave Karst Nature Preserve in the Hill Country where precipitation moves towards the recharge zone via streams Recharge Zone: area of highly fractured outcropping limestone, which enables water to flow into the Aquifer Artesian Zone: area where the Aquifer is confined  WATER USE Non-consumptive: diversion of water which is used for some purpose but is ultimately returned to the same supply Consumptive: permanent removal of water from its immediate water environment  WATER POLLUTION Water can be polluted by point sources (e.g., pipe leak, oil well leak, etc.) and non-point sources (involve more dispersed runoff mechanisms)  WATER POLICY Clean Water Act passed in 1972 made it illegal to discharge pollutants from a point source without a permit Conservation Easements are a voluntary agreement where a landowner is paid to preserve the natural condition of lands  ONGOING & FUTURE WATER STRATEGIES Since some regions face a water deficit, water transfer projects help improve dependability The Vista Ridge Pipeline moves water from the Carizzo-Wilcox Aquifer in Burleson County to Bexar County Reduces reliance on Edwards Aquifer Mainly serves houses in Stone Oak area  ONGOING & FUTURE WATER STRATEGIES Water conservation (using less water) and water efficiency (more effective use of water) can both help reduce water demand SAWS programs have reduced water consumption from 225 GPCD in 1982 to 117 GPCD in 2016  ONGOING & FUTURE WATER STRATEGIES Since most water is in SAWS Desalination Plant the ocean, desalination (removing salt from the water) is gaining more attention as a potential water source It is expensive and energy intensive  KNOWLEDGE CHECK 4 You get two attempts with your highest-grade counting Covers Topics 7 & 8 Due Wed Oct 9 @ 11:30 am *** No Class Oct 7th *** WEATHER SYSTEMS GES 2613 Topic 7 – 09/25/24  QUESTIONS FOR TODAY What are air masses and how are they relevant to weather? How do lifting mechanisms work? What are the various life cycle stages of midlatitude cyclones? How do destructive weather systems form?  METEOROLOGY Meteorology is the scientific study of the atmosphere’s physical characteristics, motions, and linkages with other Earth systems Weather is the short-term day to day condition of the atmosphere How does this differ from climate?  AIR MASSES Weather is often created by different air masses, with distinct temperature and moisture characteristics, colliding together Air masses take on the characteristics of their source region  AIR MASSES Classifications based on moisture: What would you call and extremely Maritime (m) dry cold air mass? Continental (c) cA Classifications based on temperature: Arctic (A) Polar (P) Tropical (T) Air masses named by moisture then temperature  AIR MASSES cP air masses are associated with cold, stable, and clear conditions mT air masses from the Gulf are warm, humid, and unstable  AIR MASS MODIFICATION The longer an air mass remains over its source region the more defined its characteristics become As the air mass moves, its characteristics evolve to more closely resemble the underlying surface  LIFTING MECHANISMS Since rising air cools adiabatically and enables condensation/ cloud formation, lifting mechanisms are important drivers of weather systems: Convergent Lifting Convectional Lifting Orographic Lifting Frontal Lifting  CONVERGENT LIFTING Air flowing into a low-pressure area converges, which forces air upwards This is the process that drives the ITCZ  CONVECTIONAL LIFTING Heating from an underlying surface (e.g., urban area, plowed field, etc.) creates buoyant air that rises Since the Sun’s radiation heats the land throughout the day, convectional lifting is often responsible for afternoon showers  OROGRAPHIC LIFTING Occurs when air is forced up a mountain On the windward slope, the rising air cools and precipitation is more likely to occur On the leeward slope, the sinking air warms and is dry creating a rain shadow Examples??? OROGRAPHIC LIFTING  FRONTAL LIFTING A front is the boundary between two different air masses It is a narrow zone of “conflict” where temperature, humidity, and winds vary to create weather The leading edge of a cold air mass is a cold front The leading edge of a warm air mass is a warm front  FRONTAL LIFTING The cold dense air behind a cold front, forces the warm moist air in front of it up quickly This abrupt rising motion can create thunderstorms and intense precipitation  FRONTAL LIFTING The warm buoyant air associated with a warm front gradually slides up over the cold air in front of it The gentle slope creates a larger area of atmospheric lifting with cloud formation and less intense precipitation  MIDLATITUDE CYCLONES Frontal collisions can develop into midlatitude cyclones, which are organized around a low- pressure center Midlatitude cyclones can move across North America and are guided by the jet stream  MIDLATITUDE CYCLONES A midlatitude cyclone generally takes 3–10 days to progress through its life cycle stages: Cyclogenesis is the first stage of a midlatitude cyclone, which starts with an initial disturbance in the stationary polar front  MIDLATITUDE CYCLONES During the mature stage, a well pronounced cold and warm front emerge with counterclockwise flow around a strengthening low-pressure center During the occluded stage, the cold front catches up to the warm front and cuts the warm air off from the surface  MIDLATITUDE CYCLONES During the dissipating stage, the occlusion becomes more pronounced, which cuts the midlatitude cyclone off from the temperature contrast that was its energy source  THUNDERSTORMS A thunderstorm is a type of turbulent weather accompanied by lightning and thunder Occur most frequently in areas dominated by mT air masses  THUNDERSTORMS Single-cell thunderstorms are fueled by the rapid upward movement of warm moist air Cumulus Stage: updraft forms initial cumulus cloud Mature Stage: strong up and downdrafts develop Dissipating Stage: downdraft cuts off the updraft and cell weakens  THUNDERSTORMS The updrafts and downdrafts in thunderstorms create areas of positive and negative charge Lightning: flashes of light resulting from the discharge of electricity built up between two oppositely charged areas Thunder: sound produced by the violent expansion of air  TORNADOES Often produced by supercell thunderstorms, which have a very strong rotating updraft A tornado is a violently rotating vortex that extends down from a cloud to the surface  TORNADOES Wind shear, the change in wind characteristics with height, starts tornado formation as a spinning cylinder of air is created at the surface The rotating cylinder is lifted by an updraft and is stretched vertically, which increases the rotation speed  TORNADOES Tornado strength is estimated based upon the damage that they do using the Enhanced Fujita (EF) scale  TROPICAL CYCLONES Tropical cyclones are rotating low pressure systems that originate over warm tropical waters Naming conventions depend on the region They are classified according to wind speed by the Saffir-Simpson Scale  TROPICAL CYCLONES Since there are essentially no fronts in the tropics, tropical cyclones are powered by warm ocean waters Hurricane season peaks in September for the Atlantic Basin  TROPICAL CYCLONES Eye: a relatively calm, generally clear area of sinking air and light winds at the center of the hurricane Eyewall: ring of tall thunderstorms that produce heavy rains and usually the strongest winds Outer Rainbands: bands of clouds and thunderstorms that trail away from the eye wall in a spiral fashion  TROPICAL CYCLONES Storm Surge: wall of seawater pushed inland by the storm Precipitation: heavy rainfall can produce flooding both at the coast and further inland Wind: strong winds particularly near the eye wall can be damaging CLIMATE CHANGE GES 2613 Topic 10 – 10/09/24  QUESTIONS FOR TODAY How do we study historical climate change? What natural factors influence climate change? What are the primary factors for modern climate change? How can we mitigate and adapt to climate change?  CLIMATE CHANGE SCIENCE Climate change science is the interdisciplinary study of the causes and consequences of climate change Study of past climates Measurement of current climatic changes Modeling and projection of future climate  PALEOCLIMATOLOGY To understand our current climate, we must know how climate varied before human-record keeping Paleoclimatology is the study of past climates dating back thousands to millions of years, which relies on proxy methods instead of direct measurements  PALEOCLIMATOLOGY – OXYGEN ISOTOPES Oxygen-16 (16O) is “light” oxygen and makes up 99% of all oxygen atoms Oxygen-18 (18O) is “heavy” oxygen and comprises 1 km in diameter) that forms at the summit of a volcano when it collapses inward after an eruption Lassen Volcanic National Park, CA Crater Lake, OR  EFFUSIVE ERUPTIONS Outpourings of low-viscosity magma that produce large lava flows from the vent and/or side vent Relatively gentle outflow produces a gradually rising shield volcano (e.g., Mauna Loa)  EXPLOSIVE ERUPTIONS Violent explosions of lava (less than effusive eruptions), gas and pyroclastics due to a buildup of pressure in the magma conduit The pressure buildup occurs because the higher viscosity magma plugs the conduit  EXPLOSIVE ERUPTIONS Mount St. Helens is one of the most widely studied explosive eruptions After the eruption, the rock that was fluidized by steam produced one of the biggest landslides witnessed https://www.youtube.com/watch?v=UK-- hvgP2uY&ab_channel=Storm  VOLCANO FORECASTING AND PLANNING Volcano monitoring systems have been deployed globally to observe developments Seismographic networks and remote sensing also assist with understanding the impacts  REMINDERS Knowledge Check 6 – Due Monday (10/28) @ 11:30 am Extra Credit Talk – Tuesday (10/29) @ 1:00 PM in MH 3.03.10 WEATHERING AND KARST LANDSCAPES GES 2613 Topic 13 – 10/28/24  QUESTIONS FOR TODAY What are the basic components that make up a hillslope? How does physical and chemical weathering happen? What are karst landscapes and how do they form?  EXOGENIC PROCESSES Exogenic processes include weathering, mass movement, and erosion Different from endogenic process Weathering is the process that breaks down rock into particles or dissolves them into water Erosion involves the transport of weathered materials Mass movement is the Arches National Park, Utah downslope movement of rocks and soil due to gravity  GEOMORPHOLOGY Geomorphology is the science of the origin, development and spatial distribution of landforms A landscape is in dynamic equilibrium, which is a balance between tectonic uplift and reduction by weathering and erosion Occasionally an abrupt change will destabilize the equilibrium through a geomorphic threshold (e.g., flood or landslide)  HILLSLOPES Hillslopes are curved inclined surfaces that form the boundaries of landforms For materials to move downslope, the forces of erosion must exceed the cohesion among particles and friction Water content can help increase cohesion  ANATOMY OF A HILLSLOPE Waxing slope is a convex surface where the hillslope is very steep A free face is a cliff where resistant rock is present The debris slope receives rocks fragments from above Waning slope is a concave surface at the base of the hillslope  WEATHERING PROCESSES The process of weathering breaks down rock into mineral particles or dissolves them into water Physical Weathering – involves mechanically breaking down the rock (e.g., freezing water cracking rocks) Chemical Weathering – dissolution of minerals into water Often work together since physical weathering increases the surface area exposed to chemical weathering  FACTORS INFLUENCING WEATHERING Rock Composition – certain rocks are softer and more soluble than others Climate – wetter, warmer environments speed up chemical weathering while cold environments enhance physical weathering because of freeze-thaw cycles  FACTORS INFLUENCING WEATHERING Slope Orientation – the way a slope faces influences insolation, wind, and precipitation which all influence weathering Vegetation – can decrease weathering by shielding rocks from raindrops and the stabilization provided by roots but roots can contribute to physical weathering  PHYSICAL WEATHERING The disintegration of rock without any chemical alteration can occur through: Frost Wedging Thermal Expansion Salt-Crystal Growth Exfoliation  PHYSICAL WEATHERING – FROST WEDGING When water freezes its volume expands, which produces a powerful mechanical force that can exceed rock strength Starts on small cracks which gradually expand via multiple freeze-thaw cycles Important mechanism in cold climates and areas of high elevation  PHYSICAL WEATHERING – THERMAL EXPANSION When rock surfaces are heated by the Sun they expand slightly and then they contract at night This loosens the rock surface and can cause it to crack away  PHYSICAL WEATHERING – SALT CRYSTAL GROWTH In arid environments, Trypophobia Warning!! evaporation leaves behind salts that from crystals The salt crystals change size with temperature and gouge out little pockets and form honeycomb formations Also a common mechanism in coastal areas  PHYSICAL WEATHERING – EXFOLIATION The process where rock peels off in sheets rather than breaking up into grains Exo = removal of outer layer Forms exfoliation domes When buried intrusive igneous rock is uplifted, pressure of overlying materials is relieved which causes the rock to crack Half Dome,Yosemite  CHEMICAL WEATHERING The chemical breakdown of the rock into its individual minerals due to: Hydration/Hydrolysis (water) Oxidation (oxygen) Dissolution of Carbonates Devil’s Marbles, Australia  CHEMICAL WEATHERING – HYDRATION/HYDROLYSIS Hydration = combining a mineral with water which changes the chemical structure but does not form a new chemical compound Hydrolysis = decomposition of a mineral by reaction with water, which produces a new mineral or chemical compound  CHEMICAL WEATHER – OXIDATION Oxidation occurs when metallic elements combine with oxygen (basically rusting) Results in a reddish hue and when oxidation removes iron it disrupts the crystal structure of minerals and makes them susceptible to additional weathering  CHEMICAL WEATHERING – DISSOLUTION OF CARBONATES Water vapor in the atmosphere dissolves carbon dioxide and produces carbonic acid When it rains, this acid can dissolve many minerals especially limestone (Calcium Carbonate) and marble (metamorphic form of limestone)  DIFFERENTIAL WEATHERING Differential weather is the process where different layers of rock weather differently even though they are exposed to the same weathering mechanisms It is responsible for landforms like arches  KARST LANDSCAPES In certain regions with extensive limestone formations, chemical weathering involving the dissolution of carbonates dominates the landscape It creates bumpy surface topography and underground caverns  KARST FORMATION Several conditions are necessary for a limestone landscape to develop into karst topography: Limestone formation must contain 80% or more calcium carbonate Joints that allow water to penetrate into the subsurface Air present between the ground surface and the water table Vegetation cover that provides organic acids to enhance dissolution  KARST LANDFORMS – SINKHOLES Sinkholes are circular depressions in the ground surface Solution sinkholes form by the slow subsidence of surface materials Collapse sinkholes occur over a period of days when a solution sinkhole collapses through the roof of an underground cave  KARST LANDFORMS – DISAPPEARING STREAMS Disappearing streams dive underground to recharge subsurface water levels This is how most water gets into the Edwards Aquifer  KARST LANDFORMS – CAVES Caves are natural underground areas large enough for humans to enter Any large cave formed by chemical processes (i.e., carbonate dissolution) is considered a cavern Carlsbad Caverns, New Mexico Natural Bridge Caverns  KARST LANDFORMS – CAVES Dripstones are speleothems formed as water containing dissolved minerals slowly drips from the cave ceiling Columns can form when stalactites growing from the ceiling meet stalagmites growing from the floor  KNOWLEDGE CHECK KC7 – Due Monday (11/4) @ 11:30 am RIVER SYSTEMS GES 2613 Topic 14 – 11/04/24  QUESTIONS FROM LAST TIME What are the basic components that make up a hillslope? Waxing slope, free face, debris field, waning slope How does physical and chemical weathering happen? Frost wedging, thermal expansion, salt crystals, exfoliation Hydration/Hydrolysis, Oxidation, Dissolution of Carbonate What are karst landscapes and how do they form? Limestone landscapes weathered extensively  QUESTIONS FOR TODAY What are the main components of a drainage basin? How do we evaluate streamflow? What mechanisms allow rivers to shape the landscape?  RIVER SYSTEMS Earth’s rivers make up only 0.003% of freshwater but they are important drivers of landscape change Fluvial processes are mechanisms involving rivers and streams Erosion – water dislodging and moving weather materials Deposition – when materials are deposited by the river  DRAINAGE BASINS Drainage basin is the portion of the landscape from which a stream receives water Water can flow overland in a drainage basin as sheetflow, which is a thin film spread over the ground surface  DRAINAGE BASINS Alternatively, water can be concentrated in rills (small groves) or deeper gullies and transported to stream channels Ridges act as drainage divides that determine which basin water will flow into  DRAINAGE DIVIDES Continental divides are a special type of drainage divide that determines what major water body runoff will flow into Rocky Mountains serve as the continental divide separating flow into the Pacific and Gulf/Atlantic  INTERNAL DRAINAGE The ultimate outlet for most drainage basins is the ocean However, some basins are dominated by internal drainage where water leaves via evaporation of subsurface gravitational flow  DRAINAGE PATTERNS Drainage density: total length of all stream channels divided by the drainage basin area Determined by geology and topography (easily erodible landscapes have higher drainage density) Drainage patterns are the spatial arrangement of channels in an area that are determined by topography, geology, and climate  DRAINAGE PATTERNS Dendritic: tree branch pattern of streams Parallel: streams flowing parallel to one another in response to steeper topography Rectangular: includes right angles and occurs in faulted and jointed landscapes  STREAMFLOW Streamflow is the volume of water flowing in a river Influenced by precipitation, temperature, snowmelt and groundwater Perennial Streams: flow all year long Ephemeral Streams: flow only after precipitation events  DISCHARGE Discharge is a stream’s volume of flow per unit of time (e.g., cfs) Amazon river has the greatest discharge Turbulent flow: occurs in streams with lots of friction and creates rapids Laminar flow: occurs in streams with less friction so water moves in organized parallel sheets  DISCHARGE OVER TIME A graph of discharge over time is a hydrograph Baseflow is the amount of discharge during dry periods which is sustained by local groundwater Peak flow is the highest discharge that occurs due to precipitation Urbanization causes the peak flow to be larger and happen earlier  STREAM EROSION Hydraulic action is the type of erosion performed by flowing water that loosens, lifts, and moves rocks/sediment Higher with turbulent flow Abrasion is another form of erosion that involves boulders and gravel moving along the channel hitting each other Maximized during floods when high flows pick up lots of debris  SEDIMENT LOAD The sand, pebbles, gravel, and boulders that a stream carries is its sediment load Higher discharge = Higher sediment load  SEDIMENT LOAD Dissolved Load: material that travels in solution due to chemical weathering Suspended Load: fine-grained particles that are held aloft in the stream Bed Load: coarser materials that are moved by traction (rolling along the streambed) or saltation (bouncing)  STREAM GRADIENT The gradient of a stream is defined as the drop in elevation per unit of distance Gradient is usually steeper closer to the headwaters and more gradual downstream at the mouth  NICKPOINTS Nickpoints are when the longitudinal profile of a stream shows an abrupt change (e.g., waterfall, rapids, etc.) Can be produced when a stream flows across a resistant rock layer or a surface deformation  WATERFALLS Waterfalls gradually migrate upstream as the more resistant strata is undercut Eventually this causes the lip to collapse and the gradient is reduced as debris gathers at the bottom  STREAM MEANDERING When the channel slope is gradual, streams weave back and forward to form meanders Maximum flow velocity is on the outside of the curve which can form an undercut bank Minimum flow velocity is on the inside of the curve so sediment is deposited to form a point bar  STREAM MEANDERING Oxbow Lakes form when the cutbank erodes through the neck separating two adjacent meanders and the old meander is gradually detached from the new stream channel by sediment infill  STREAM DEPOSITION Stream deposition occurs when a stream deposits sand, gravel, silt, etc. which forms depositional landforms (e.g., floodplains, terraces, deltas) High velocity streams transport larger materials so coarser items settle out closer to the headwaters and only finer sediment makes it to the mouth  DEPOSITIONAL LANDFORMS – FLOODPLAINS Floodplains are the flat low-lying areas adjacent to a channel that are inundated frequently When the water recedes, it leaves sediment deposits that are often fertile  DEPOSITIONAL LANDFORMS – NATURAL LEVEES When a river exceeds its banks, the stream spreads out and slows, so it drops coarser materials immediately along the banks After multiple floods, these coarser materials build up and form a natural levee  DEPOSITIONAL LANDFORMS – RIVER DELTAS A river’s velocity rapidly decreases at its mouth where it enters a larger standing water body A river delta is the deposition of sediment at the mouth as the coarser materials fall out first and finer sediment travels further Selenga River Delta (Lake Baikal)  DEPOSITIONAL LANDFORMS – RIVER DELTAS Arcuate Delta: has an intricate maze of channels running through an arch shaped delta Estuarine Delta: delta that is filling an estuary (where fresh and saltwater meet) Bird’s Foot Delta: has a few widely spaced channels that extend long distances into the main body of water  FLOODS A flood is when water passes over the natural banks of a stream Recurrence intervals are used to define flood probability 100–year flood = 1% chance a flood that size happens in a given year  FLOODS https://www.bexarflood.org/#!/main/map/2138 Fluvial Flooding: occurs when rivers overflow their banks Pluvial Flooding: happens when the ground is saturated with water from rainfall Tidal Flooding: caused by the sea and tidal rivers