Note: Please observe this geological feature from the posted coordinates and do not venture beyond the gate, even if it is open. Binoculars may be helpful, but are not absolutely necessary.
Approximately 2 million years ago, the ice ages began. There is some thought that since then, 20-30 different ice sheets have covered Maine and New Hampshire. However, the only evidence left in this region is from the last great ice age that began about 25,000 to 30,000 years ago and retreated from this area about 11,000 years ago. This was a time known as the Wisconsin Glacial period.
The ice sheet that covered Maine and New Hampshire during this period, known as the Laurentide Ice Sheet, was at least 6,500 feet thick and may have been even thicker. Geologists know that the ice sheet covered the top of Mt. Washington, New Hampshire's highest peak at 6,288 feet, so it was definitely thicker than that elevation.
At glacial maximum, approximately 18,000 years ago, the ice sheet extended from northern Canada to the New England continental shelf and covered all of Maine and New Hampshire. Sea level at that time was 200-300 feet lower than today. When the climate changed, rapid melting of the ice sheet occurred and sea level rose.
The weight of the ice sheet depressed the Earth's crust beneath it, so when the ice melted, sea level rose faster than the Earth's crust could rebound. By the time the ice margin had melted back to the present position of the Maine coast (about 13,000 years ago), the rising sea had caught up to the retreating ice front and flooded the depressed crust of coastal Maine. The coastline was as much as 100 miles farther inland than it is at present, and the edge of the glacier floated as a shelf of ice over what is today coastal Maine. The formation of great meltwater streams flushed sediments being shed from the melting ice onto the shallow seafloor. These glacial deposits in the shallow seawater formed moraines, deltas, and glacial mud flats.
The area you see before you at the posted coordinates was formerly a glacial delta. Deltas are found all over southern Maine and record the elevation of the water in which the sediments were deposited. These formations contain layers of sand and gravel and are mined today for construction materials, primarily for roads and highways. Because these sediments were deposited along the former shoreline, they don't contain any of the silts and clays that were carried further offshore. That makes these sand and gravel deposits perfect for use as building material because they are permeable to water.
To log this Earthcache, please send an email to me via my profile page. Please do not reveal any of the answers in your log. The email must be received within a couple of days of logging your find. Any logs not accompanied by an email will be deleted. Also, all geocachers must send their own email to get credit for this find. Do not state in your log that another geocacher is emailing the answers for you because your find will be deleted.
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Please state the name of the cache in the first sentence of your email.
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From the posted coordinates, estimate the width of this sand/gravel pit either in feet or tenths of a mile (whichever unit is more comfortable for you is acceptable).
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Estimate the depth of the pit at the deepest point. (Hint: you may want to use a tree or some other object as a reference point for comparison to estimate the depth).
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Glacial deltas have deposits that are stratified (layered) as opposed to till which is a mixture of various sediment sizes (silt, sand, gravel, cobbles, etc.) all mixed together. At this site, what evidence can you see of layering?
Thank you for completing this Earthcache. You may notice many other areas in southern Maine that consist of glacial deposits, both similar to and different from this particular site.