Glaciers in Rhode Island -- Dr McConeghy

Matanuska Glacier in Alaska -- meltwater lake on top of the glacier-- mmcconeghy

Glaciers in Alaska? Yes, sure! But, how do we know there were Glaciers in Rhode Island?

1. Till and boulders

photo mmcconeghy Alaska 1999

This photo actually shows recently deposited till at the foot of Matanuska glacier in Alaska, but the image should be familiar to anyone who has hiked around New England.

Till is rocks that have been deposited by the glacier as it melts. The rocks are typically a mixture of all different sizes and shapes: some have been rounded off as they have been carried along by the ice, and further eroded by the water rushing out of the melting glacier. The glacial Till is often spread out into "braided" streams where it is further eroded and sorted. The rushing meltwater sorts the till into different sizes, rolling large boulders into piles, and carrying sand and silt further downstream than mid-sized rocks.

Big glaciers move a lot of rocks, and we have many places in New England where you can see glacial boulders that have been moved by the ice.

huge truck-sized boulder, Lincoln Woods, RI

pile of car-sized boulders, Exeter, RI

these watermelon-sized boulders were built into a wall by an Indian stonemason about the year 1670, Exeter, RI. Stone walls are a familiar sight in New England.

2. Eskers

Eskers -- mmcconeghy

An Esker is a kind of odd-shaped small hill which is found in territory where a large glacier has melted.

Eskers are formed when melting ice creates rivers within the body of a large glacier. The melt water carves a channel within the glacier and deposits sand or gravel along the channel as any stream or river would do.

When the glacier melts completely, the sand within these channels can create a long, snake-shaped curving hill. Some of these hills in New England resemble a winding railroad embankment or fortification -- about 20 feet high, thirty or forty feet wide and 100 yards or more long. Some eskers are much larger.

In Providence you can see excellent examples of eskers in the North Burial Ground on North Main Street, and in Roger Williams Park.

an Esker in the North Burial Ground in Providence RI. It is 100 - 200 meters or so long, about ten meters wide and about 6 - 8 meters high.

3. Glacial Scarring

Glaciers pick up broken rock from the hills they pass over. The broken rock is frozen into the glacier ice and as the glacier travels downhill, it scrapes the rock on the ground.

glacial scarring of a rock in Lincoln Woods, RI mmcconeghy

Sometimes you find glacial scarring in an unexpected place... here is a rock from Mauna Kea volcano in Hawaii that shows glacial scarring. Most people don't realize that Hawaii had a glacier in ancient times.

Glacial scarring of a rock at Mauna Kea volcano, Hawaii. Although it is much further south than Rhode Island, at over 13,000 feet this tall volcano was high enough to have a glacial covering at its peak thousands of years ago. (photo: mmcconeghy)

4. Glacial Trains

When a glacier passes over a hill, it breaks rock from the hill and carries it along. Then, when the glacier melts, it deposits the broken pieces 'downstream.'

One of the most recognizable glacial trains in the world is in Rhode Island. This occurs because a location in Cumberland, RI called Iron Mine Hill has a deposit of unique iron ore. The composition of this ore, Cumberlandite, is different from any other iron in the world, so it can be easily recognized and identified.

We find broken pieces of cumberlandite in a train reaching from Iron Mine Hill down into the Atlantic Ocean at the southern end of Narragansett Bay.

5. Bottom Cores

The mud deposited in the bottom of ponds and lakes is often formed in layers, formed annually during the different seasons of the year, very similar to the way circular yearly rings are formed in the wood of the trunk of trees. We can examine the mud from the bottom of New England ponds and lakes. When we do, we find that: 1) there are not nearly as many layers of mud in New England ponds as in some ponds in the southern US. 2) the lowest,oldest layers of the mud samples are very different from modern layers. The layers from 12,000 years ago have silty deposits characteristic of water running off glaciers, and they are sterile -- no remains of life. This is a big contrast with deep samples from ponds in the South -- 12,000 year old layers in the South have much the same composition and contents as modern layers.. 3) as you examine the layers from Northern ponds you find that as you look at layers closer and closer to the surface, the samples have pollen, leaf fragments, insect parts and occasionally a hair or tiny bone from an animal. Older layers have cold weather animals and plants, while more recent samples (of say, 3000 years ago) have more or less the same components as modern deposits.

If you think about these differences, you will realize that they tell a very clear story -- New England was covered with ice until about 12,000 years ago. The ice melted, gradually plants and animals moved into the area. The plants and animals that lived here were first cold weather types, but as time went on, different animals and plants suitable for warmer climates took over until we came to have the ecosystem that we recognize today as temperate forest.

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