Rogen moraine

A Rogen moraine, also known as a ribbed moraine, is a subglacial landform primarily found in Fennoscandia, Scotland, Ireland, and Canada. These are one of three main types of hummocky moraines and occur over large areas once covered by ice, typically in the central regions of former ice sheets. Named after Lake Rogen in Sweden, their type locality, they form groups that are closely and regularly spaced.

Composed mainly of till, a glacial drift, Rogen moraines appear as large, wavy ridges oriented transverse to ice flow. Drumlins often accompany them, suggesting a concurrent formation process. Typically, these moraines range from 10–30 meters in height, 150–300 meters in width, and 300–1,200 meters in length.

The exact formation mechanism remains unclear, but several theories have emerged since the 1970s: they may form from megaripples eroded during subglacial floods; reshaping of existing landforms due to a 90-degree ice flow shift; shearing or folding of debris-rich basal ice; sediment wave growth under glaciers; or fracturing of sediment sheets during glacier thermal changes.

Given the diversity in their morphological features, multiple formation processes might be valid. Theories proposing origins near glacial margins, such as end moraines or calving in lakes, have been largely dismissed.