River Series 3

Question 1

In topographically low parts of the landscape ______, ________, and _________ sediments are deposited

Answer 1

valleys, pidemonts, coastal plains

Question 2

Fluvial sediments are laid down, and depositional landforms are created at:

Answer 2

• Dominantly or partially subaerial conditions
• Topographic discontinuities
• Valleys and the margin of water bodies

Question 3

Restricted lateral movement and confined within the valley

Answer 3

upstream channel

Question 4

Channels are able to shift positions over wide areas

Answer 4

Near baselevel

Question 5

Arid to Semi-Arid Environments
Large Sediment Supply
Occurs in Fault fronts, Tectonic Mountain Fronts or Sudden Topographic Discontinuities
General gradient: 3-6°
Marginal screes: ~30°
Near the apex: ~10°

Answer 5

Alluvial Fans

Question 6

Upper part is incised passing outward to braided streams. Generally poorly sorted sediments near the head due to torrential deposition. It becomes better sorted sediments outwards with finer grains

Answer 6

Fan structure

Question 7

Conglomerates/unsorted sediments near the head, with bettering sorting and finer-ing of sediments outwards.

Answer 7

Sediment mechanics of alluvial fans

Question 8

Exhibits complex cross-bedding and Flow Structures

Answer 8

Bedding

Question 9

an size should be related to the size of the sediment source area AKA drainage basin.

Answer 9

Growth of fans

Question 10

Have a smaller fan, compared to fans underlain by mudstone and shale

Answer 10

Geology influences the relation, in a drainage basin e.g underlain by sandstone

Question 11

Fan surface is not dissected. Relatively smaller than fans of perennial streams

Answer 11

Dry fans

Question 12

Streams flows through incision. Coarser materials are rarely carried downstream. River widens downstream, braided. Progressively shifting channel

Answer 12

Wet fans

Question 13

Where alluvial fans are large enough, or sufficiently closely spaced, they may coalesce laterally to produce a depositional bed. To produce a __________.

Answer 13

Peidmont zone or Bajada

Question 14

Mainly are terraces and floodplains of a river. Normally finer upward. Channels are mainly braided to meandering though some other rivers

Answer 14

Valley fills

Question 15

Change in positive baselevel change: resulting into the backfilling of the
Uplift or Change in climate: resulting into increased sedimentation, sediment load progressively moves down the system
Uniform filling of the valley: increase in production of sediments from the numerous tributaries

Answer 15

Valley Filling

Question 16

Enumerate the channel types in valley fills

Answer 16

Meandering
Anastomosing
Braided
Straight

Question 17

Sinuous Channels
Near Baselevel
Low Gradient/Flat
Fine Sediments (Mainly suspended loads and dissolved loads)
Shifts laterally

Answer 17

Meandering channels

Question 18

Low Bedload discharge
Low sinuousity
Low bedload unless due to incision

Answer 18

Straight

Question 19

Relatively permanent
Cohesive banks, Sinuous channels
Diverges/Converges around stable, vegetated bars

Answer 19

Anastomosing stream

Question 20

High sediment supply
High Gradient changes
Low stability

Answer 20

Braided

Question 21

Enumerate the causes of braiding

Answer 21

Overloading of sediments discharge

Steep slopes which produce a wide shallow channel where bars and islands form readily

Easily erodible banks which permit widening at high flow

Large bed material load, in comparison with its suspended load where large material is immobile except during high flood stages

Question 22

Alluvial surface adjacent to a channel that is frequently inundated. Highest elevations normally occurs on the abandoned levee and point bar ridges

Answer 22

Floodplains

Question 23

Occasionally be formed by the incision of bedrock surfaces, but they are most likely the remnants of floodplains trenched by rivers. Caused by negative baselevel changes- resulting into headward surges of rejuvination

Answer 23

River terraces

Question 24

______ may represent reworking and may contain heavy mineral concentrations

Answer 24

Terrace sediments

Question 25

Formed when sediment-laden rivers flow into standing bodies of water.

Answer 25

Deltas

Question 26

Geomorphic Characteristics of deltas are determined by the following factors:

Answer 26

Relative densities of the river water and standing water River hydrology and variations of discharge The amount and caliber of river load esp. bed load and suspended load Intensity of coastal processes, particularly: wave action, longshore currents and tidal scour Geometry of the slope Vertical tectonic stability Climate

Question 27

The dynamics of the delta morphology is strongly influenced by the relative densities of the inflowing and standing waters

Answer 27

Delta morphology

Question 28

Carries large proportions of fine suspended load Usually occurs to the snout of tide water glacier Submarine slumps produce turbidity currents: Graded beddings

Answer 28

Hyperpycnal

Question 29

Typically is when rivers flow into freshwater lakes. Devoid of significant tidal or wave forces Bedload settles immediately

Answer 29

Homopycnal

Question 30

Rivers flow into saltwater (most common) Coarse bedload is deposited near the mouth as leeves Fine suspended load carried seaward in the surface which spreads over the sea Produces gently sloping submarine delta front

Answer 30

Hypopycnal

Question 31

Floodplain sands and silts; marsh organic deposits; platform sands.

Answer 31

Topset

Question 32

Cross-bedded coarser sands and silts of the delta slope, together with channel fingers- grading laterally into clay and marsh deposits and sand splays

Answer 32

Foreset

Question 33

Offshore clays, toeslope turbidity silt deposits

Answer 33

Bottomset

Question 34

Deltas are dominated by the removal of river debris by wave or tidal currents Wave Influenced/Dominated Tide Influenced/Dominated

Answer 34

High destructive

Question 35

Deltas are dominated by large debris supply from the river Lobate/Fan Elongate/Bird’s foot

Answer 35

High constructive

Question 36

Flattened in a pan Rapid removal of debris by strong longshore currents

Answer 36

Wave dominated

Question 37

Funnel Shaped distributaries Open and straight distributaries

Answer 37

Tide dominated

Question 38

Much of the debris is coarse Distributaries change in position similar to alluvial fans Compact distributaries

Answer 38

Lobate fans

Question 39

Delivers large quantity of fine sediment Builds out Constantly shifting

Answer 39

Elongate/ Birds foot delta