New Hampshire Geology New Hampshire Bedrock Map

Neocene Period page 1
(1.8 million years ago - Present)
Formerly known as the Quarternary Period


The Pleistocene Epoch
So Little Time, So Much To Do

The Pleistocene Epoch is the vast majority of the Neocene Period. It lasted from 1.8 million years ago until about 10,000 years ago.

If the Geologic Timeline were laid out on a 100 yard football field, the Neocene Period would be the last inch and a half, with the Pleistocene Epoch taking up all but the last 1/64th of an inch!  

The inch and a half would represent approximately 1.8 million years of geologic time.  In that time, there would be at least four separate episodes of advancing and retreating glaciers that, together with the debris they scooped up and brought along with them, would have the combined effect of 'polishing' our mountains and exposed bedrock to a new level of roundedness and smoothness.  

Many mountains took on the shape of roche moutonees (roash MOO-ton-ays). That's a French term meaning 'rock sheep' - because roche moutonees look like sheep lying on the ground!

Cannon Mountain is a classic roche moutonee. The northern and western side is a gradually rising slope. Its southern and eastern sides features cliffs and a talus slope. This is where the profile of the Old Man of the Mountain was located.

roche moutinee
The roche moutonee, or sheep's back shape of Cannon Mountain

(Click on the image for a closer look.)|
Image credit: Daniel E. Reidy

Glaciers started to form approximately 1.8 million years ago at the beginning of the Neocene Period.  

Glaciers form when the climate gets cool enough so that not all of a winter's snow melts in the summer. The snow starts to accumulate year after year.  As more and more snow stays behind, more and more sunlight is reflected back into space making the area even cooler.  This increasing coolness fosters more snow accumulation and less melting.  It becomes a vicious cycle that creates snow packs more than a mile thick!

Natures Sandpaper

The overlying weight of the upper snow levels cause the lower levels of the snowpack to turn to ice, embedding sand, gravel, and rocks of all sizes in the underside of the glacier.  

These bits of sand, gravel and rocks make the glacier behave like sandpaper. It smooths out the landscape as the glacier starts to move outward along all its edges due to the weight of the ice pack at the center of the glacier.

Ice alone cannot wear down mountains and leave scratches (striations) in bedrock.  

Try rubbing ice cubes on a brick. You won't notice much, if any, effect on the brick. Try this experiment again with ice cubes that have sand and gravel in them. You'll notice the difference!

The Glacier's Calling Cards

In the days before telephone answering machines and email (yes, there was a time without these electronic wonders), people wishing to do business with you would actually show up in person (what a concept).

If they happened to miss you, they would leave a small calling card with their name, phone number and address on it to let you know they had come by.

The last advance and retreat of the glaciers left several calling cards on our landscape.  

The glacier's passing has created many of today's landforms such as kettle hole ponds, eskers, kames, boulder caves, talus slopes, drumlins, glacial valleys and deltas.  

Glaciers also caused flooding of coastal portions of our state and the drowning of forests, the transportation of large boulders from one area of the Northeast to another (glacial boulders and glacial erratics), the creation and the drainage of vast glacial lakes, and the openings of gaps, or notches in the mountains.  

Some of New Hampshire's weathered and eroded bedrock (sand made up of quartz granules from weathered and eroded granite) ended up at the leading edge of the greatest advance of the ice sheets and become part of what is today Cape Cod, Martha's Vineyard and Nantucket Island.

  nauset cliffs
The cliffs at Nauset Beach on Cape Cod.
(Click on the image for a closer look.)
Image credit: Daniel E. Reidy

Note the layers of sand that were deposited from the edge of the melting glacier during summers at the end of the Ice Age.  Some of this sand may have come from New Hampshire.

Kettle Holes

Kettle hole ponds and lakes formed when large chunks of the receding edge of a glacier fell off and got buried by sediments washing out from the glacier's meltwaters.  

When the ice chunk finally melted, it left  a depression in the ground that filled with the glacial block's meltwater and rainfall and snow melt.

A well known example of a kettle hole lake in New Hampshire is Ossipee Lake.

Ossippee Lake as seen below from the summit of Mount Bayle in the Ossipee Mountains.

(Click on the image for a closer look.)

Image credit: Daniel E. Reidy

Talus Slopes

Cannon Mountain in Franconia Notch contains a classic example of a talus slope.  

A talus slope is a steep slope made up of boulders from collapsed cliffsides.  The boulders are pried loose through the actions of freezing and thawing of water in fractures in the rock.  

The fractures occur naturally due to thev expansion of the granite dome.  The granite dome was originally created miles underground.  The erosion of miles of overlying rock has relieved the pressure on the granite, causing it to expand.  

As it expands it cracks into layers, much like that of an onion.  Daytime heating and nighttime cooling also cause the exposed rock to expand and contract.  All of this contributes to the breaking up of the cliff face and the massive rock slides, called mass wasting, that occur periodically.  This process of the pealing and removal of the rock layers is known as exfoliation.  

These layers are clearly visible in the photo below.  This is how the profile of the Old Man of the Mountain was both created and destroyed. (The Old Man's rock slide is visible on the far right edge of the mountain as the smaller of two lighter colored streaks in the talus slope. )

(Click on the image for a closer look.)|
Image credit: Dan Reidy

Erratic or Not?

A glacial erratic is a boulder of one rock type sitting on bedrock of another type.  A glacial boulder is a large rock sitting on top of bedrock of the same type.  In both cases, it was glaciers that transported the boulders from where they formed to where they rest today.

In the town of Madison is one of the largest glacially transported boulders in the world, the Madison Boulder.  It is 87 feet long, 23 feet wide and 37 feet high.  How does this compare with your classroom?  With where you live?

The Madison Boulder is made of Conway granite and it sits on Concord Granite Bedrock.  Is it a glacial boulder or a glacial erratic?

madison boulder

(Click on the image for a closer look.)|
Image credit: Dan Reidy

Pleistocene Scene

Below is a map of the Earth during the Pleistocene Epoch showing the furthest advance of the ice sheets.

(Click on the image for a closer look.)|
Image credit: Christopher Scotese

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