{{short description|Rock formation caused by glaciers}} A '''washboard [[moraine]]''', also known as '''minor''' or '''corrugated moraine''', is a [[geomorphic]] feature caused by [[glacier]]s. The name "washboard moraine" refers to the fact that, from the air, it resembles a [[washboard (laundry)|washboard]].
== Formation == The exact washboard formation mechanism is not known. One theory proposes that as the glacier melts it leaves behind an accumulation of rock debris in the form of annual recessional moraines. These annual glacial advances and recessions cause parallel ridges to form a few metres apart. Because the accumulation of debris is annual, the moraines do not get very large and stand only a few metres high.
An alternative theory is that basal [[till]], weakened by high pore water pressure, deformed upwards into parallel basal [[crevasse]]s a short distance in from the glacial margin.<ref>{{Cite journal |last=Price |first=R. J. |date=1970 |title=Moraines at Fjallsjökull, Iceland |url=https://www.jstor.org/stable/1550139 |journal=Arctic and Alpine Research |volume=2 |issue=1 |pages=27–42 |doi=10.2307/1550139 |jstor=1550139 |issn=0004-0851 |archive-date=2016-06-04 |access-date=2017-09-18 |archive-url=https://web.archive.org/web/20160604171842/http://www.jstor.org/stable/1550139 |url-status=live |url-access=subscription }}</ref><ref>{{cite journal | last1 = Alley | first1 = R.B. | year = 1991 | title = Deforming bed model for southern Laurentide till sheets?. | journal = J. Glaciol. | volume = 37 | issue = 125| pages = 67–75 | doi = 10.1017/S0022143000042817 | doi-access = free }}</ref><ref>{{cite journal | last1 = Cline | first1 = M.D. | last2 = Iverson | first2 = N.R. | last3 = Harding | first3 = C. | year = 2015 | title = Origin of washboard moraines of the Des Moines Lobe: Spatial analyses with LiDAR data | journal = Geomorphology | volume = 246 | pages = 570–578 | doi=10.1016/j.geomorph.2015.07.021| bibcode = 2015Geomo.246..570C }}</ref> Crevasse fields of similar geometry to fields of washboard moraines have been observed on ice shelves of Antarctica experiencing large amounts of longitudinal extension, similar to the stresses that would have been experienced by the glaciers that formed these moraines.
== Examples == Washboard moraines can be seen in many places such as South Dakota, Iowa, Maine, and Iceland.
== References == {{reflist}}
[[Category:Moraines]] [[Category:Glaciology]] [[Category:Sediments]] {{glaciology-stub}}