Glacial Deposit Resources of the Northeast



All four regions of the Northeast share a common source of non-mineral resources: the deposits left by glaciers of the most recent ice age. For the last 1.8 million years, a continental ice sheet originating in northern Canada has advanced and retreated over North America. Around 20,000 years ago, a warming climate put the glaciers in retreat, bringing the Northeast to its current interglacial period. Deposits associated with the massive, moving and melting ice remain today as valuable non-mineral resources in the Northeast. The glaciers covered the northern parts of all four regions of the Northeast as far south as northern Pennsylvania, New Jersey and Long Island.

The main non-mineral resources resulting from the last glacial advance are clay, peat, soil, sand and gravel. As the glaciers moved over the surface of the Northeast, they scraped and gouged the landscape. The numerous lakes dotting the Northeast resulted from the vigorous scouring activity of the glaciers. Much of the clay mined today in the Northeast comes from the bottom of these glacier-formed lakes. Used in bricks and pottery, the glacial clays are an important natural resource of the Northeast. Clay is also commonly used in place of heavier stone and gravel to make a lightweight concrete. As the glacial lakes filled and later drained to become bogs and swamps, organic material accumulated at the bottom. Bogs and swamps are ideal environments for the accumulation of dead plants. Kept wet and buried by more dead plant material, the stagnant water of a bog provides little if any oxygen for bacteria to completely decompose the plant material as it would on the forest floor or in a flowing stream. The resulting peat, a precursor to coal, is mined and used as mulch and as a soil conditioner. 

The glaciers also left deposits on the surface on which the Northeast soils have developed. In combination with the underlying bedrock, the glacial deposits contribute good and bad characteristics to the soil (from the perspective of cultivation). Till, the unsorted mix of sand, silt, clay and gravel that was deposited by melting glaciers, developed into impermeable soils that cannot properly drain water. The unsorted material has no spaces between particles, leaving nowhere for water to drain. Likewise, clay deposits from glacial lakes are also impermeable, being uniformly composed of very small, flat clay particles. Glacial outwash deposits of sand and gravel, on the other hand, are generally well sorted and thus well-drained.

The soils developed in the Northeast are a direct result of the underlying rock type and transported glacial sediment. Glacial clay, till, sand and gravel blanket much of the region and affect the permeability of soil. Also, the reason why New Englanders find so many rocks in their farms and gardens is because the glacial till became incorporated into the soil. The till has since become incorporated into the famous stone walls of New England.

Perhaps the most important resource left to the Northeast by the glaciers is sand and gravel. Dominating the natural resource economies of many of the Northeast states, sand and gravel is an extremely abundant, easily mined natural resource of the area. Naturally broken rock the size of sand and gravel was dumped all over the Northeast landscape by the glaciers. As the glaciers advanced over the landscape, their vigorous scraping action incorporated boulders, gravel, sand, silt and clay from the underlying bedrock and already loose sediment into the moving ice. Each time the glaciers stopped moving forward or backward, melting ice deposited drift and till in front of and to the sides of the glacier, creating mounds (called moraines) of sand and gravel. Significant deposits of sand and gravel were produced by deltas formed by glacial streams and in valleys filled by retreating glaciers. Sand also accumulated in snake-like tunnels beneath the ice, in which sand was deposited by flowing subglacial streams; these sinuous deposits of sand are called eskers. Glacial sand and gravel are easily mined because the glacial deposits are all at the surface and there is little if any processing involved. Sand and gravel composed of chunks of limestone, dolostone, sandstone, metamorphic and igneous rocks are mostly used for construction purposes. Shale and siltstone, being softer rocks, are generally too weak for construction, and are more often used together with lime in making concrete.