A Sollefteå "Nipa"
Today we drove to Sollefteå, about 90 km north of our village. It was a grey day with desultory rain drops falling out of the clouds, not very inspiring but considering the forecast it could have been worse!  One of Sollefteaå's features are the “nipa”, mounds of naturally cemented sediment, usually very steep sided and up to 50 meters high. Despite much searching I cannot find a English term for these features.
Naturally I’m blipping one of these mounds. This one is typical, about 40 meters high and very steep. The holes you see are the nesting holes of birds - sand martins I believe.
So what is a “nipa”? Having blipped it I thought I better find out what they are. I found that they seem to be a fairly unusual feature, which is maybe why there is no English name for them. If you get bored by glaciology/geology explanations stop here...
20,000 years ago the northern European Ice sheet was at its thickest here. The 3000 metre thick ice sheet pushed the bed rock down into the crust of the earth. As the ice started to melt huge quantities of sediment filled water flooded down what today is the Ångerman river.  As the river met the sea the sediment dropped and formed a large delta. Then the land started to rise because the weight of the ice was gone. (So far the land has risen 185 meters.) The delta was lifted out of the sea, so in many places, beneath the modern forest floor is an unremarked 50 meter thick layer of glacial sediment. However, where the river and its tributaries continued flowing they cut down through the sediment, on their way to the now distant sea.  As the river, and its tributaries flowed they sometimes changed course and the result is many of these steep sided mounds of naturally cemented sediment.
Mostly they just sit there, an unusual feature only of interest to nerdy types like myself. They are stable enough that houses and roads have been built on them or right next to them. However, occasionally they collapse, particularly if they are undercut by a stream or river, or after a very wet summer and then they tend to make the local news!