Landform Geography Fluvial Systems and Landforms
Overland Flow & Drainage Basins Hydraulic Geometry & Channel Flow Fluvial Processes & Landforms Human Interactions with Streams
Overland Flow Perennial Streams – water runs all year Ephemeral Streams – water runs only part of year Sources of stream water: –Groundwater –Melting Ice –Surface Runoff
Drainage Basins Drainage Basin – area contributing groundwater and runoff to a stream Drainage basins are divided from each other by topographic barriers called watersheds Drainage Divide – elevated terrain forming rim around a drainage basin Drainage basins vary tremendously in size Basins are nested, smaller within larger
Small, Nested Drainage Basins
Common Drainage Pattern Types
Major US Watersheds
Drainage Density Total length of all streams Drainage Density = Area of drainage basin
Stream Ordering Represents stream size Smallest streams in basin order 1 – order rises when 2 streams of same order come together at confluence
Hydraulic Geometry Geometric attributes of river channels Variables: –w = channel width –d = channel depth –v = velocity of water –s = slope (steepness) also called gradient –Q = discharge (amt of water flowing) –Q = w x d x v (units m 3 /s or ft 3 /s)
Hydraulic Variables
Stream Hydrograph Graph showing fluctuation in stream discharge over time Lag between storm event and highest discharge Base flow – flow rate sustained by groundwater influx
Flooding Flood Stage – stream discharge increases so that water spills out of channel onto adjoining ground Return Period – time between events of a given magnitude, e.g. annual flood, 50-year flood, 100- year flood Larger floods occur less frequently
Mississippi River Floods At least 100-year flood, perhaps a 500-year flood Heavy winter rains saturated ground Stationary high pressure in Southeast in summer, blocking mid-latitude jet stream over Midwest Cool, dry air collided with warm, moist air along jet stream, creating constant precipitation Precipitation ran off into stream channels & rivers
Mississippi River Floods
2009 Carrollton Floods
Fluvial Processes and Landforms Running water is most important geomorphic (landform shaping) process on Earth’s surface All landforms due to either erosion or deposition Erosional landforms occur when sediment, soil, or rock is stripped away from land Depositional landforms occur where sediment accumulates after being dropped
Depositional vs. Erosional Landforms
Hillslopes Most active zones of fluvial erosion due to high relief creating fast-moving, powerful water Rills Gully
Ravine Canyon
Landforms Geography Glaciers
Glacial Geomorphology Development of a glacier Types of glaciers Glacial landforms
Development of a Glacier
Glacial Mass Budget
Glacial Movement
Glacier Types
Continental Glaciers
Glacial Landforms Rock & debris picked up by glaciers, transported in direction of movement & deposited Glacial erosion: –Glacial Abrasion – scratch and gouge bedrock –Glacial Striations – caused by glacial abrasion –Glacial Grooves – deep striations –Glacial Plucking – boulders ripped from ground by glacier – deposited by retreating glacier, called Glacial Erratics
Glacial Erosional Landforms Glacial grooves Roche Moutonnee Glacial striations
Alpine Erosional Landforms Glacial Erosion: –Cirque – bowl-like feature on mountain flanks –Tarn – small lake in bottom of cirque –Arête – narrow, steep ridges between cirques –Horn – mountain with 3 or more arêtes at summit –Glacial Trough – u-shape valley eroded by glacier
Alpine Erosional Landforms
Glacial Depositional Landforms – Glacial Drift Glacial Till – sediment directly deposited by glacier – many particle sizes Moraine – winding ridge formed by till at the front or side of glacier – Moraine types: –Lateral – along former edges of glacier –Terminal – along front of former glacier –Recessional – formed as glacier recedes –Medial – between 2 glaciers –Ground – irregular deposition as glacier recedes
Glacial Depositional Landforms (Till)
Glacial Depositional Landforms (outwash) Glacial Outwash – sediments deposited by water out & under a glacier as it melts – forms Outwash Plain, flat feature in front of former glacier Kame – large mound deposited near glacier front Esker – winding ridge from water flowing in tunnel through ice under glacier Kettle Lake – big ice block fallen off glacier front is buried by outwash, melts later forming lake
Glacial Depositional Landforms