Dune types > Barchans

• Basic dune shape.

• Erosion (and gentle slope) on upwind/windward side.

• Deposition (and steep slope) on downwind/leeward side.

• Horns point downwind.

• Formed where winds are consistent and sand supply is limited. Often seen alone.

• Wind is coming from upper left to lower right in the photo; Dune is propagating towards lower right.

• Free dunes

• Scarce sand

• Consistent and effective wind from one direction

• Single slipface

• Horns of crescent point downwind

Barchanoid Ridge

• merged barchans

Dune types > Longitudinal Dunes

• Dunes run along the direction of the wind.

• Barchan horns of great length.

• High wind, limited sand.

• Usually seen in swarms.

• Hard to tell they're longitudinal dunes from ground-level.

• Winds variable in one direction

• Ridge forms parallel to consistent wind direction

• two slipfaces

• 100 – 400 m tall, up to 100 km long

Seif

• Sharp crest

• shorter in height

Dune types > Transverse Dunes

• Transverse to wind.

• Forms where there is lots of sand.

• Barchans merged left to right (stretched out across wind)

• Hard to tell if they're transverse dunes from ground-level.

• Free dunes

• Abundant sand supply

• Less effective wind

• Consistent direction of the wind

• Single slipfaces

Dune type > Parabolic Dunes

n Tied dune

n Vegetation stabilizes movement

n Consistent wind direction

n multiple slipfaces

n crescents point upwind

Dune type > Star dunes

• Pyramid of sand with radiating ridges (multi-arm star-shaped)

• Indicates three of more "prevailing" wind directions, often in monsoonal climates and near edge-effects like topographic barriers at edge of a dune area

• Winds variable in all directions

• Multiple slipfaces

• With effective winds, form high mounds

• With less effective winds, form networks of connected sinuous arms.

17. Describe the geological activity of the running water

Running water is the most important geologic agent in eroding, transporting and depositing sediment

Nearly every landscape on Earth shows the results of stream erosion or deposition

18. Describe the drainage systems of rivers

Drainage basins

· Drainage basin - the total area drained by a stream and its tributaries

· Tributary - a small stream flowing into

· a larger one

· Divide - ridge or high ground that divides one drainage basin from another

· Continental Divide separates the streams that flow into the Pacific from those that flow into the Atlantic and Gulf of Mexico

Drainage patterns

· Drainage pattern - the arrangement, in map view, of a stream and its tributaries

· Most tributaries join the main stream at an acute angle, forming a V or Y pointing downstream

· Dendritic - drainage pattern resembling the branches of a tree

· Radial pattern - streams diverge outward like the spokes of a wheel

· Typically form on conical mountains (volcanoes)

· Rectangular pattern - tributaries have frequent 90° bends and join other streams at right angles

· Trellis pattern - parallel streams with short tributaries meeting at right angles

19. Describe the river channel patterns, erosion by streams and deposition

Date: 2015-12-11; view: 918