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Landforms of the Fluvial System. Objectives Describe formation and characteristics of alluvial fans Examine landforms formed by fluvial erosion and deposition.

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Presentation on theme: "Landforms of the Fluvial System. Objectives Describe formation and characteristics of alluvial fans Examine landforms formed by fluvial erosion and deposition."— Presentation transcript:

1 Landforms of the Fluvial System

2 Objectives Describe formation and characteristics of alluvial fans Examine landforms formed by fluvial erosion and deposition in river valleys Investigate the evolution of river deltas

3 Introduction Fluvial landforms built by: – Deposition – Erosion

4 Alluvial Fans Ephemeral streams emptying from mountain valleys construct alluvial fans Alluvial fans are fan-shaped – Formed of alluvial material – Debris flows in upper alluvial fans More common in deserts – But can form in humid areas

5 Flow and Deposits on Alluvial Fans Flow emptying from valley spread – Velocity decreases, sedimentation occurs – Unconfined water spreads across fan in shallow channel Deposits are poorly stratified – Thick near mountain – Thin outward from mountains Alluvial fans coalesce to form bajadas Older parts of fan may develop desert varnish/pavement

6 Landforms of River Valleys- Meandering Rivers Bends in sinuous channel termed meanders – Erosion on outside of bend – Deposition on inside of bendPt bar – Grow and migrate – Cut-off meanders form oxbow lakes

7 Landforms of River Valleys- Meandering Rivers Formation of oxbow lakes

8 Landforms of River Valleys - Braided Rivers River with multiple channels separated by sand or gravel bars Braiding forms by deposition of bar in mid- channel – Water flows around bar forming two channels High sediment load, steep slopes, variable discharge, loose bank materials may cause braiding

9 Landforms of River Valleys - Floodplain Flat, low-lying ground bordering channel Frequently flooded and sediment deposited – Levees form on channel margin Eroded by migrating meandering Growing pt. bar rebuilds floodplain

10 Landforms of River Valleys - Floodplain Widening of floodplain and devleopment of large meanders in meander belts

11 Landforms of River Valleys - Floodplain Flooding and levee development

12 Human Use of Floodplains Farming Development People do not adjust well as risk grows Flood control measures – Artificial levees, dams – Provide mostly artificial security – Must assume floods will recur

13 Terraces Benches above modern floodplain – Are older floodplains Develop through stream incision of floodplain – Lower floodplain develops – May have paired or mostly unpaired terraces May have aggradation before terrace formation – Increased sediment supply causes – Reduced sediment supply then results in incision – Fill terraces produced

14 Terraces Aggradation and terrace development

15 Deltas Triangular shaped deposits where streams empty into oceans or lakes – Coarse sediments deposited at river mouth – Fine sediments carried farther – Distributary channels form transporting water and sediments Delta form depends on: – Discharge and sediment transported – Configuration of seafloor – Strength of currents, waves, tides

16 Delta Types

17 The Delta Profile Consists of bottomset, foreset, and topset beds Compaction may occur causing subsidence


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