Moving Water

When Water Moves...


When water moves it really is quite a powerful force on this planet.  A vast quantity of water on Earth is continually moving between the ocean, the atmosphere and the land.  Water is stored in large quantities in the ocean, on the land in lakes and ponds to which it arrives after traveling over the land in rivers and streams, and in the form of ice in large polar ice caps.  Additionally, throughout history large quantities of water have been trapped on the land in the form of great sheets of ice during many "Ice Ages" in times past.  During these times, the most recent of which began about two million years ago, large continental glaciers slowly ground over the land, shaping the landscape and depositing large quantities of material on the land and on the ocean floor.  Over the past two million years or so, the ice sheets have advanced and retreated over twenty times.  The most recent period of glaciation ended about twelve thousand years ago.  

Water has the ability to affect the landscape in either its liquid or its frozen form.  Liquid water moving over the land causes rocks to be weathered, or broken down into smaller pieces, transported over the land in moving water through the process of erosion, and deposited in other locations,  forming new rocks, in the processes of deposition and lithification.

Wave action may also break down and transport the rocks upon which they crash.  Wave erosion and deposition are responsible for forming many coastal features and depositing shoreline structures, including beaches.

The slow and steady force exerted on Earth by Ice moving slowly across its surface is responsible for much of the landscape that you see around you.  During the most recent period of glaciation during the last Ice Age, large glaciers, as much as two miles thick, covered much of the northern hemisphere, in this area, the ice extended as far south as New York.  The glacier that covered Maine and New England was nearly two miles thick in areas, and it moved ponderously under its own weight.  Though glaciers such as this don't move very fast, they have a lasting effect upon the land.  The glaciers moving across Maine erased most geological features that were formed earlier, leaving behind a new landscape loaded with clues about its icy origin.  Long scratches, called Glacial Striations, can be seen in many large areas of rock.  These scratches were caused when the glacier slowly ground its way over this rock, leaving behind scratches caused by rock embedded in the ice.  The direction of these scratches shows the direction that the glacier was moving.  Maine's mountains tend to have a profile where the sides are gently sloping to the northeast, and sharply jagged on the southwest.  This is caused by the slow movement of the glacier in this direction.  The sides of the mountain facing the glacier were slowly worn away until they were the gentle slopes we see today.  The side of the mountain facing the back of the glacier is often jagged, and many cliffs are present.  These are caused by the glacial action known as "plucking", where the retreating ice rips large chunks out of the stone as it passes.  Torrents of water flowing beneath the glaciers often deposited sediments in long ridges called eskers.  Many of Maine's earliest roads were built on the natural ridges formed by the eskers.  As the glacier reached the sea, and began to melt, large chunks of boulders would be deposited in random fashion.  These boulders had been carried by the ice sheet for many miles, until finally being deposited as the ice melted.  These large, seemingly out of place, boulders are called "glacial erratics". Perhaps you've seen "Bubble Rock" in Acadia National Park?  Here, a huge boulder the size of a house is perched right at the edge of a cliff several hundred feet high.  Though the boulder seems ready to tumble down the slope at any moment, it's rested in exactly the same position since the melting glacier deposited it there, about twelve thousand years ago.   The slow grinding movement of the ice sheet caused rock to be ground into smaller pieces.  This glacial till was deposited in Maine and became some of our rich farmlands, so important to the economy of Maine today.  Other glacial till formed economically important gravel pits, many still being used today to expand the network of roads in our state.  The melting ice sheet smoothed  out our mountains and hills, and gouged out our coastline,  deposited large amounts of till on the floor of the Gulf of Maine, helping to make it the incredibly productive fishing area it is today.  
The island of Long Island, in New York, was another result of the melting Ice Sheet.  As the glacier melted, long ridges of material were deposited near its edge.  These structures are called "End Moraines", and Long Island is a prime example.  Rocky debris was collected in the glacier's steady southward march.  As the ice melted, this debris was deposited at the glacier's edge.  Some of this material became the underwater banks, such as Georges' Bank, which separates the Gulf of Maine from the open Atlantic Ocean, and helps to make the Gulf of Maine one of the world's most productive fishing areas. Still more of this rocky debris would one day become known as "Long Island".  Look at Long Island on a map, you can see in it's outline, theancient footprint of the glacier that once would have covered this area in over a mile of ice.