Landscape Evolution in Humid Climates
Steven Dutch, Natural and Applied Sciences, University
of Wisconsin - Green Bay
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The picture here shows the evolution of landscapes in humid climates.
- The top left diagram shows the youthful stage. Rivers are
deepening their valleys but there is flat land between the valleys because
small streams have not yet had time to erode deep channels. The river
valleys are steep sided and V-shaped.
- The top right diagram shows the beginnings of the mature stage.
Valleys are still steep sided and V-shaped but have widened so that adjacent
valleys meet in sharp ridges. The rivers have cut as deeply as they can and
the landscape has maximum relief.
- The lower left diagram shows the later part of the mature stage. Rivers
can no longer cut their valleys deeper but erosion still affects the
surrounding landscape, causing ridges to round off and become lower. The
river wanders in its valley and creates a flood plain.
- The lower right diagram shows the old age stage. The landscape
has been reduced nearly to a flat plain called a peneplain. Resistant
masses of rock may stand up as isolated hills called monadnocks.
Since the river course is very flat, the river meanders, and
occasionally the river breaks through the necks of meanders to leave cutoff
C-shaped lakes called oxbows.
This cycle was first suggested over 100 years ago, and there are places where
landscapes have followed this script. However, there are many things that affect
- In many places, uplift of the land can reset the cycle or rejuvenate
- During the last two million years, ice caps have repeatedly formed and
taken water out of the oceans, lowering sea level and causing rivers to
deepen their valleys. Then the ice caps melt, raise sea level, and the
valleys fill in with sediment. So most of the world's rivers have been
repeatedly rejuvenated in the last couple of million years. The places that
best seem to fit this ideal cycle of landscape evolution are the interiors
of tropical continents, far enough inland for rivers not to have been
affected much by changes in sea level, and where climates have been fairly
- Meandering rivers are not necessarily ancient. Rivers meander because
they flow on flat land. The land may be flat because it is very ancient, but
it can also be flat because it is covered with recent deposits of sediment.
The lower Mississippi River meanders but the land surface dates only from
the end of the last ice age.
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Created 05 February 2008, Last Update
25 May 2011
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