### formation | ridge:

Sand dune
* Some sand dunes provide shelter.
  * are made when wind or a river pulls sand into a mountain-like shape. They can be found in deserts, but sometimes high up on beaches too.
* Watch how the fan makes dunes, pits, and sandstorms in the desert sand.
* act as buffers to erosion.
* are a vital part of our fragile ecosystem
  - accumulations of windblown sand piled up in mounds or ridges
  - an important part of coastal ecology
  - big hills of sand
  - conspicuous and spectacular features of many desert landscapes
  - found around the world, in varying types of climates
  - huge piles of sand blown there by strong gusts wind
  - mostly longitudinal, following the dominant wind directions of a high pressure cell
  - some results of wind's hard work
  - the main surface features in the northeast and southwest
  - very susceptible to damage by foot or vehicular traffic
  - vital to protect against beach erosion, which is why picking sea oats is illegal
  - well-known in poorly vegetated areas
* arrange themselves in parallel rows.
* can have a negative impact on humans when they encroach on human habitats
  - merge and split, and in so doing can change their shapes, and produce new offspring
* cover about half of the land.
* develop as a result of swirling winds around beach plants
  - their own type of plant succession called a psammosere
* form a line of defense, protecting marsh and woodlands from high tides and storms
  - along the shores of Lake Michigan
  - in many areas
  - protective bluffs with the help of swaying sea oates
  - some of the most spectacular and dynamic landforms on the planet
  - where there is an abundant source of sand available for movement by wind
* line the coast at The Gambia's southern border with Senegal.
* occupy only a fraction of the Saharan landscape.
* occur in many places on the earth from deserts to beaches
  - some areas
  - throughout the world, from coastal and lakeshore plains to arid desert regions
* provide a habitat for several rare plant species
  - numerous areas for primitive camping
* stretch in both directions.

### formation | ridge:

Sandbar
* also affect the outward flow of water
  - provide food and shelter for shorebirds, waterfowl, mammals, amphibians, and reptiles
* are bars
  - important for basking and egg laying sites
  - offshore shoals of sand deposited with slower moving water
  - preferred nesting habitat
* includes inclines
  - sections
  - slopes
* obstruct the mouths of all rivers, making entrance hazardous.
* often form in areas where longshore currents frequently occur.
* sharks lives in shallow coastal waters.
* support a variety of plant and animal life during the dry summer.

Wrinkle ridge
* are features created by compressive tectonic forces within the maria.
* occur in all mare regions and form circumferential or medially transecting patterns.

### formation | ridgeline:

Arete
* are people
* are sharp edged ridges between adjacent cirques
  - ridges eroded by glaciers
  - the sharp ridges leading away from horns

Riverbed
* are beds.
* provide habitat for a variety of species.

### formation:

Rock formation
* Many rock formations show repeating patterns of strata.
* Some rock formations are just below the surface
  - develop the unusual property of fluorescence
* range in color from dark red and orange to light purple and pink.
* slow process that has been occurring throughout geologic time.
+ Rhythmite, Longer-term rhythmites: Geology
  * Many rock formations show repeating patterns of strata. This is usually caused by repeating cycles of climate. In warmer times the sea rises, and carbonate rocks are deposited in shallow subtropical seas. Later, ice builds up at the poles and the sea level drops. Then the same area is close to shore, and gets sand and mud washed down by rivers.