Adirondack Park Agency

Geology of the Adirondack Park

The Adirondack Dome

The Adirondack Mountains are very different in shape and content from other mountain systems. Unlike elongated ranges like the Rockies and the Appalachians, the Adirondacks form a circular dome, 160 miles wide and 1 mile high. Although the Dome as we know it today is a relatively recent development, having emerged about 5 million years ago, it is made of ancient rocks more than a 1,000 million years old. Hence, the Adirondacks are "new mountains from old rocks."

Birth of a Glacier

A quarter of a million years ago, when the earth was a few degrees cooler, the snow which fell in the winter did not melt entirely in the cool summers. As it accumulated over millennia, its enormous weight compressed the lower layers of snow into ice, eventually becoming thousands of feet thick. The increased pressure softened the lower ice, causing it to flow like thick molasses. A glacier was born.

Shaping the Landscape

As the ice advanced southward into the Adirondack region, soil and rock was scraped from the land and embedded in the ice like sand in sandpaper. Alternately scratching and smoothing the earth's surface, the glacier pulverized boulders into pebbles, carrying the debris as it moved. As it thickened, the glacier crept over hills and, eventually, over the highest mountains, breaking and lifting rocks as it rounded their summits. When the ice sheet melted, these rocks, called erratics, were deposited throughout the Adirondacks, where they can be seen today in fields, along forest trails, and scattered on mountaintops.

Glacial Landforms

Alpine Glaciers, Cirques, and Horns

As the massive continental glacier grew to the north, small alpine glaciers were forming in the Adirondack Mountains. These alpine glaciers carved the upper slopes of the mountains for thousands of years. Gradually, they became buried by the advance of the continental ice sheet. The distinctive summit of Whiteface Mountain owes its shape to alpine glaciers. Bowl-shaped amphitheaters called cirques were carved from the rock on the north, east and west sides of the mountain by three separate alpine glaciers. Where the tops of the cirques joined, sharp ridges, called aretes, were formed. If this process had continued, the cirques would have ended up back-to-back, leaving a horn, and Whiteface Mountain would now look like the Matterhorn in Switzerland.

Kettle Holes & Kettle Ponds

As the glacier thawed, iceberg-sized chunks of ice broke off and were buried beneath accumulating sand and gravel washed from the ice. When these ice blocks melted, they left depressions - kettle holes - in the landscape. When a kettle hole went below the water table, a kettle pond was established as the steady supply of water remained in the basin. Many of the small, circular ponds and wetlands in the Adirondacks were created in this fashion.

Eskers and Kames

Meltwater streams, flowing under and within the glacier through tunnels in the ice, built their own stream beds from rock material embedded in the glacier. After the glacier melted, these riverbed sediments were deposited on the landscape as winding ridges called eskers. When sediment-laden water flowed over the glacier's surface, it filled depressions with sand and gravel. As the glacier melted, material from circular depressions was deposited on the landscape as mounds called kames.


Adirondack soils are young, having developed only since the glacial retreat about 10,000 years ago. Unglaciated areas in the rest of the United States have soils that have developed over millions of years. Soils in the Adirondacks are generally thin, sandy, acid, infertile, and subject to drought.

Forest Soil

Forest soils have a layer of leaves, needles, twigs and other plant and animal parts covering the mineral soil. This organic debris accumulated with every season and, as it slowly decomposed, it recycles nutrients back to the growing plants. The mineral soil provides plants with solid anchorage for their roots and a secondary source of nutrients. Tree roots will grow in all directions within the soil in search of water, nutrients and support. Root growth will continue as long as the soil temperature is greater then 40 degree F and roots are not limited by rock or compacted soil, or by soil so water-saturated that it contains no oxygen for the roots.


The melting ice sheet created huge, sediment-laden rivers that roared across the Adirondacks, depositing sand and gravel outwash on giant, shifting floodplains. Coarse gravels and boulders settled on river bottoms; lighter sand particles, silts and clays were carried downstream. As the glacial rivers changed velocity and direction, layers of these various outwash materials built up on top of one another, forming the sedimentary strata normally found in valleys and lower elevations today.


The debris that was deposited directly on the land by melting glaciers without being carried and stratified by meltwater streams contained unsorted rocks of all shapes and sizes. These are referred to as till. Because they have not been smoothed by the movement of the meltwater stream, till materials are often rough and jagged.

Four Basic Ingredients

Soil is made up of four components: mineral and rock particles, decayed organic matter, live organisms, and space for air and water.

Minerals and Rocks

The mineral component of soil ranges from fine clays to rocks. The upper mineral layer - topsoil - may have organic matter incorporated into it. The lower mineral layers, or horizons, are collectively called the subsoil.

Organic Matter

Dead plants and animals and their waste products, in varying stages of decomposition, provide the organic component of soil. These horizons exist near the top of most forest soils.

Live Organisms

From microorganisms - bacteria, fungi, and protozoa to earthworms, soil organisms may account for 5 tons of living tissue per acre. These organisms aid in the essential enrichment of soil by destroying plant residues, decomposing the dead bodies of all organisms, and mixing and granulation soil particles.

Pore Space

Healthy soil promotes the recycling of nutrients from mineral and organic material to live organisms. This transfer occurs in the voids between materials in the soil, in the spaces for air and water, often called, collectively, pore space. Typically, topsoil has 50 percent pore space in its mix of organic and mineral materials. Growing conditions are ideal when soil pore space holds equal parts of air and water, allowing room for root expansion, diffusion of nutrients, and movement of soil life.

Soil Horizons

Soils are formed by the action of plants and animals and the physical breakdown of minerals, called weathering.
Plant and animal material which accumulated on the surface of the ground is decomposed by numerous micro-organisms. The by-products of the process are organic acids that are washed into the ground, making the soils acidic. These acids dissolve and transport organic matter, iron, and other elements into the soil, to a depth of one or two feet on the better drained sites. Organic matter accumulates to form blackened layers in the soil; below, iron accumulates to form red/rusty colored layers.

Formation of Water Systems

Melting ice, glacial debris, and changing glacial topography contributed to the continual disruption of the meltwater drainage system of the Adirondack region. Lakes and ponds were formed as ice debris dammed river valleys; as dams broke, sand and gravel were redistributed downstream. This process left glaciated regions like northern Minnesota, Wisconsin, and the Adirondacks dotted with thousands of beautiful, natural lakes. Yet for all this reconfiguration of the landscape, the major drainage patterns of the Adirondack Dome were essentially unchanged by glaciation. Taking the path of least resistance, Adirondack waters drain from the central high country to the region's periphery. Water flows east from the mountains to Lake Champlain, northwest to the St. Lawrence River, west to Lake Ontario, and southward to the Hudson and the Mohawk rivers, as it did before the arrival of the glaciers.

Rivers and Streams

Water is both the workhorse of the sun and the lifeblood of the living world, flowing in an endless cycle through the landscape. Continually replenished in flakes of snow, drops of rain and dew, or moisture condensed into clouds and fog, water links all the plant and animal communities of the Adirondack Park. Wherever it falls to earth, water moves downhill in response to gravity. Rivulets and trickles join brooks, which combine to form streams and rivers. Nearly 30,000 miles of streams and brooks that emerge from the mountains and forests form the network from which 1,000 miles of powerful Adirondack rivers gather their volume and strength. These rivers and their networks are perhaps the greatest multiple-use natural resources in the Adirondacks. They provide habitat for fish and wildlife from the kingfisher to the salmon to the otter. In the past, they were the vessels of transport for pulp and provided power for sawing logs into lumber for market. They also were the trade and travel corridors that set the pattern of settlement of Adirondack hamlets that we still see.

Riffles and Pools

In their mountainous headwater reaches, most streams fall steeply through narrow v-shaped channels in the shallow soil and bedrock, developing swift-running riffles that alternate with deeper, more sluggish pools. Riffles, places of high energy where air and water freely mix, charge stream water with oxygen. Pools are quieter areas where organic materials tend to collect and decompose, consuming oxygen in the process. This allows the vital recycling of nutrients necessary for living organisms in the stream. One after another, watershed streams join force, forming rivers that link the mountains with the sea.
The river carries sediments eroded from the hills down to the flatland, where, as it slows and meanders, it deposits its bounty in the slack water of bends or along the floodplain. Lakes and Ponds Flowing and still water has always been an integral part of the Adirondack landscape. But the lakes and ponds we know today are relatively young, resulting from the retreat of the last glacier, the Wisconsin, only 10,000 years ago. Each lake and pond is a separate ecosystem composed of a community of plants, animals and microbes living together in a stillwater environment. Ponds are typically shallow enough for sunlight to reach across their entire bottom; lakes usually fall off into darkness, where rooted aquatic plants cannot grow. Coldwater lakes are often deep and clear, with steep sides and rocky or sandy bottoms. Because light does not penetrate all the way to the bottom, relatively little plant growth takes place. Warmwater ponds are typically shallower, with gently sloping sides and thicker, organic-rich sediments. Their shoreline offers a fertile environment for aquatic plant growth.

More about the Adirondack Park...

Natural Communities
Adirondack History