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Landforms of the Fluvial System

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Presentation on theme: "Landforms of the Fluvial System"— 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 bend—Pt 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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