Glacial Moraine

Glacial moraine consists of soils formed over sandy glacial till and generally of the steeper soils formed over water-sorted sand and gravel.  Glacial moraine is as much a landform designation as a geologic designation.  The moraines are the hilly parts of Suffolk County, and the topography is characteristically that of many hills and depressions.  Since the engineering properties of the course-grained sand and gravel arenot very different, regardless of geologic origin, their engineering characteristics are determined to a large degree by their topographic differences. 

Among the differences between the till and outwash is the amount of fines in the soil.   The glacial till contains more silt-size and clay-size particles that the water-sorted glacial woutwash.  This generally decreases permeability, decreases conmpressability, and increases the strength of the soils.  Boulders and cobblestones are also scattered throughout the soil.  The wider range in gradation results in smaller voids and a more conpact soil.  A relatively compact layer is called a fragipan.

The topography of the moraines is perhaps the most severe limitation for engineering works.  Because of its hummocky nature, cuts and fills are necessary for almost any project.  The relative compactness of the glacial till makes excavation more difficult than in water-sorted materials.  The course grained soils have adequate strength for high embankments.  Settlement is by rearrangement of the particles rather than by the removal of water, and it generally occurs during construction. 

Depressions, or kettleholes, are within the moraines.  These depressions contain organic matter, silty inwash from the surrounding knobs, or water.  The organic should be removed if is not possible to bypass the depression.

Drainage of surface water on the moraines is almost exclusively by infiltration.   Where the fragipan occurs and where the under lying till is reached, infiltration is retarded.  Poorly drained areas are in the low places.

Many of the soils that formed over the glacial till are good sources of topsoil because of their large content of silt.  they have not been exploited to any degree for granular materials.  Extensive water-sorted deposits are in the moraines, and such areas provide such large quantities of sand and gravel.  Fill material from the moraine is good because the additional content of silt allows greater compaction. 

Soil Survey of Suffolk County, New York. 1975
United States Dept. of Agriculture, Soil Conservation Service, in cooperation with Cornell Agricultural Experiment Station