a long, narrow, sinuous, steep-sided ridge composed of irregularly stratified sand and gravel that was deposited by a subglacial or supraglacial stream flowing between ice walls, or in an ice tunnel of a retreating glacier, and was left behind when the ice melted —note eskers range in length from < 1 km to > 160 km (< 0.6 to > 99.4 mi), and in height from 3 to 30 m (9.8 to 98.4 ft) This definition last updated 10/26/2008