Anomalous landscapes amid local forest

This is quite something. For some reason known only to geologists, the large forest to northwest of Hipolitów and southeast of Sułkowice contains a hilly ridge running through a landscape that's largely flat. Pines, birches and oak trees dominate the hillsides. The contoured sandy soil is exposed to the elements with several areas each of a couple of thousand square metres appearing to be sand pits.

I visited this fascinating landscape last Wednesday and again this morning, catching a train one stop south to Sułkowice and walking home (on Wednesday I did it the other way around – walked out, train back).

Below: a most unusual sight for this part of Mazovia; I am immediately reminded of Oxshott Heath, a frequent family weekend destination in my childhood, and the forests and dunes around Stella-Plage in northern France.

Below: trekking uphill, suddenly the vista opens up to a vast sand pit.

Below: the second sand bowl, to the northwest, this one popular with the quadricyclist community. Aerial images of this feature show that a lake can form at the bottom; it's now totally dried out without a trace. 

Below: after sunset on Wednesday evening, 25 September, the destination of my equiluxial walk. 

Below: and a few minutes later; dusk descends upon the scene. Through the forest I return to Sułkowice in darkness. It's 3km from here to Sułkowice station; I'm in good time to catch the 19:08 train; three minutes later and I'm back in Chynów.

Below: from geoportal.gov.pl, an orthophotographic map of the area showing the raised land snaking across a flat landscape, with the sand pits gouged out from the hillsides. The questions are: what geological event caused this S-shaped formation to rise some 20 metres above the surrounding flatlands? And were these sandpits once commercial excavations of building sand? (The sandpit at Oxshott Heath was originally dug to fill sandbags used in WW1.) 

Below: from Google Earth Pro, satellite imagery from 2011 and 2020. The maps can be aligned with the orthophoto above by means of the forest road running southwest to northeast. Note how their shape and size had changed over those nine years.

UPDATE 30 SEPTEMBER: My brother Marek points out that this feature is called an esker (in Polish, an oz). The Polish page is interesting in that it says that such features are found in the Grójec district.

"An esker or os is a long, winding ridge of stratified sand and gravel, examples of which occur in glaciated and formerly glaciated regions of Europe and North America. Eskers are frequently several kilometres long and, because of their uniform shape, look like railway embankments."

Below: fragment of a geological map of Poland, the forest west of Sułkowice enlarged, and within lies an elongated feature in orange marked with the number 35. As with many maps offered by the Polish state, there's no legend explaining what the numbers mean, but the location and the shape tally (compare the orange squiggle with the orthophoto above), so I can only guess that all features with the number 35 are indeed eskers, serpentine shapes in a sea of numbers 40 and 38. Whatever those are.

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