Landform Geography

Fluvial Systems and Landforms

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 DensityTotal length of all streamsDrainage 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 m3/s or ft3/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 - 1993

• 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 - 1993

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 waterRills 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 Mass Budget

Glacial Movement

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