Landforms of Rivers, Ice, Wind and Sea

Patterns:

• Dendritic: like the veins of a leaf, tributaries joining at acute angles. Forms on uniform rock and a regular slope. The most common pattern.
• Trellis: main streams parallel, short tributaries joining at right angles. Forms on folded rock.
• Rectangular: streams bend at right angles along joints and faults.
• Radial: streams flow outward from a central high point, such as a volcano or dome (Amarkantak).
• Centripetal: streams flow inward from all sides into a lake or depression (Loktak Lake).

Kinds of stream:

• Consequent: follows the original slope of the land.
• Subsequent: follows lines of weak rock structure.
• Resequent: flows the same way as the consequent stream but at a lower level.
• Obsequent: flows opposite to the consequent stream.
• Insequent: has no clear reason for the path it takes.

Landforms by stage:

• Youth: V-shaped valleys, gorges (deep, steep-sided) and canyons (deep, with step-like sides), waterfalls and rapids.
• Maturity: meanders (looping bends), a wide floodplain, braided channels where the river splits around bars.
• Old age: oxbow lakes, natural levees, deltas.
• A meander is a loop-shaped bend. The outer bank is eroded and the inner bank built up. A very tight meander is a gooseneck; a flood can cut through its neck and leave an oxbow lake.
• Rejuvenation: uplift of the land (or a fall in sea level) makes the river cut down again. It gives incised or entrenched meanders, knick points and river terraces.
• River terraces are flat steps marking old valley floors or floodplain levels. They may be bare bedrock or covered with alluvium, and they are made by the river cutting down (erosion).
• A wind gap is a dry notch in a ridge where a river once flowed before it was captured. Despite its name it is made by a river, not by wind.

Glacial landforms:

• Cirque: an armchair-shaped hollow at the head of a glacial valley. A lake in it is a tarn.
• Glacial trough: a U-shaped valley. Alpine glaciers strip the valley of its soil, regolith and sediment to make it. Parts of its floor can be flat, where lake and outwash deposits filled it in after the ice left.
• Fiord: a glacial trough whose floor lies below sea level, so the sea floods in as the ice retreats (Norway).
• Moraines: ridges of rock debris dropped by the ice. Eskers: winding ridges of sand and gravel laid by meltwater. Drumlins: egg-shaped mounds.

Periglacial landforms (frozen ground near ice sheets):

• Pingo: an ice-cored mound pushed up through permafrost.
• Patterned ground and solifluction lobes also form here.

Wind (aeolian) and desert landforms:

• Zeugen: a table of hard rock standing on a softer base, left after wind cut away the soft layers.
• Yardang: a long ridge of rock cut by wind, lying along the wind's direction.
• Mushroom rock or demoiselle: a rock with a narrow stem, worn at the base by blown sand.
• Dreikanter: a stone with three faces polished by wind.
• Inselberg: a lone residual hill on a desert plain. Playa: a flat, dry lake bed in a basin. Bajada: a gentle apron of joined alluvial fans at the foot of a desert mountain.

Coastal landforms:

• Wave erosion makes cliffs, arches and stacks (a pillar of rock left standing in the sea).
• Barrier islands are long, narrow ridges of sand lying close to and along the shore, cut off from the mainland by lagoons or marshes. Storms and hurricanes easily wash over them, so they are risky places to build.

Limestone (karst) landforms:

• The sinkhole (doline) is the most common karst landform: a hollow from under a metre to a few hundred metres deep, made by limestone dissolving.
• Also caves, stalactites (hanging) and stalagmites (rising).