meander river and underfit river?

Question

does someone know how the meander river becomes an underfit river ,
I only know taht when the discharge reduces( when ice retreat ......climate chagens ) , the ability of the water to erode its channle reduces , then , it vbcomes an underfit river

thanks

Answer 1

Also called "misfit river"--river is much smaller than expected for the width of its valleys--very common in areas that were once glaciated.
In the United States and Canada, several rivers are much smaller now than when they received vast outflow of water from glacial melts during the Ice Ages when there were vast continental glaciers covering Canada and the Great Lakes area. So, during Pleistocene time, the river systems cut wide valleys that seem not to "fit" the current volume of water flowing through the rivers.
Minnesota River: "Some 9,000 to 12,000 years ago, the Glacial River Warren flowed with great volumes of meltwater from the southern end of the Glacial Lake Agassiz. Those icy currents carved the wide, trough-like, loam-covered valley of the Minnesota River that we see today."
http://www.environmentaleducationohio.org/Biosphere/Case%20Studies/minnesota.html
Milk River: "Most of the canyon cutting took place when virtually all of the runoff from southwestern Alberta was being diverted into the Milk River as a result of blockage by ice of drainage to the northeast. With recession of the Laurentide glacier out of the region and opening of a route around the Cypress Hills, evolution of the modern South Saskatchewan drainage began, waters that previously were feeding the Milk River became incorporated into the Hudson Bay catchment basin" (Beaty, 1975)." http://www.uleth.ca/vft/milkriver/milk_river.html
Illinois River:"the old valley is exceptionally wide for the size of the new river. After the last glacier retreat ed, the Illinois permanently shrank to a much smaller river, fed only by rainfall and seepage from underground aquifers. The pulse of the river changed. In years with average rainfall, backwater lakes rose and expanded, temporary ponds developed, and grass lands became marshes in late winter and early spring. The water then drained out slowly; by midsummer the river flowed only in the main channel and much of the floodplain was dry again. "
http://dnr.state.il.us/orep/c2000/assessments/lower_sangamon/page4.htm.
Upper Mississippi River.

You can imagine drought, stream capture, and similar phenomenon causing a decline in flow.