Notes on the Sand Dunes of Northwestern Indiana

Abstract

Of the sand dunes of North America, few present more interesting phenomena than those bordering the southern shore of Lake Michigan. Not only do they illustrate all phases of dune activity but they have a significance in ecology and post-glacial history as well as rare scenic beauty. They are conspicuously developed in northwestern Indiana, their maximum development being confined to the 20 miles of shore between Gary and Michigan City. Heights of 1oo feet are common and the height of the frontal ridge along the lake commonly ranges from 75 to 175 feet. Parts of the dune complex are fixed and forested, while in other areas the sand is being shifted. The dunes are limited largely to a belt about a mile wide along the shore, although in places low dunes extend several miles inland. Along the western shore of Lake Michigan for 20 miles north of Chicago the waves are actively cutting into the thick drift, here composed of rather fine materials. This wave-cut cliff may be seen on the Highwood topographic map and in places is more than 80 feet high. A very considerable amount of erosion has taken place and some of the debris has been transported southward by the alongshore currents. Evidence of this movement is seen in the accumulations of sand on the northern sides of piers and the southerly deflectiofi of streams entering the lake where unprotected by breakwaters. With the wear and sorting involved in the transportation, the material which reaches the southern end of the lake is almost exclusively quartz sand. Here the topography and prevailing winds are such that deposition takes place. The shore sands become the prey of the winds and the dunes reach their greatest development. In order to examine the effect of the wind transportation on the sand grains, nearly fifty samples were gathered along seven lines