esker
A long, narrow, sinuous ridge created by deposits from a stream running beneath a glacier.
Another unusual ice-contact feature is an esker, a long, narrow, steep-sided ridge of glaciofluvial sand and gravel inhabiting a glaciated area. Eskers tend to follow valleys and lowlands, carefully picking a course between obstacles.
Where it comes from
From Irish eiscir (“esker, glacial ridge”).
Adapted from the Wiktionary entry esker (CC BY-SA 4.0).