Birch Point Pocket Beach EarthCache
Hidden : 2/3/2010
Difficulty:
2.5 out of 5
Terrain:
2.5 out of 5

Size: Size: other (other)

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Geocache Description:


Welcome to Birch Point State Park one of Maine's great coastal attractions where you will enjoy some of the most spectacular scenery on the Mid Coast including a classical example of a pocket beach. Located south of Ash Point on a very small peninsula along the Mussel Ridge Channel, Birch Point State Park affords the visitors majestic views of Penobscot Bay and the islands that lay past the channel. Ash Island rests to the north while the Mussel Ridge Islands rest to the south. Two Bush Island Lighthouse rests south of the island farther out into the Atlantic Ocean, while Whitehead Light is tucked closer to shore almost due south of the park.

The story of this earthcache begins approximately 421 million years ago with the formation of the white rocks of the Spruce Head pluton. This was once a large mass of molten rock that solidified deep underground, which was then exhumed by uplift and erosion over geologic time. The glacial ice then shaped the smoothly sculptured surface of the rock that you see on both sides of the beach. This rock surface has essentially remained unchanged since about 14,000 years ago, although sea level has changed dramatically in that time. It is these rocky headlands that have created what is known as a “pocket beach.”

The fact that this pocket beach is built on a base of cobble makes it extremely stable. Most sediment is suspended in seawater and transported along the coast by the longshore current, a stream of water flowing parallel to the beach that is created by the action of waves breaking at an angle to shore. In the second process, sand deposited onshore by the longshore current is then oscillated by waves breaking onto and receding from the beach. This continual onshore-offshore movement gradually pushes the sand along the beach edge. Seasonal cycles of sand deposition and loss dramatically affect the appearance of beaches from summer to winter. Wide and gently sloping in summer, they become steep-fronted and narrow in winter, and can vanish overnight, stripped of sand by violent storm waves.

While this is a sand beach there really is not a great deal of sand present. Unlike most coastal beach that have dunes formed from the wind, the dunes at this beach were formed in a major storm some time ago. The dunes at the head of this beach are made of cobbles, moved by high-energy storm waves.

The small waves and gently surf on the incoming tide gently wash the sand up the beach toward the dunes. At low tide, fresh water seeps from behind the dune and forms small streams that wash the sand back down the beach, exposing the cobbles beneath. The small streams that run down the beach face move side-to-side as they deposit sand in their own shallow channels. Because of the resulting pattern, this is called a "braided stream." These small channels are accentuated by concentrations of pinkish-red garnet. The lighter colored, less dense grains of quartz and feldspar sand are washed to the side leaving the pattern that you see when you visit the beach.

At the posted coordinates you will find yourself at the head of the beach on the cobble beams. The lowest layer represents a less violent storm. The most violent storm in the recent history of the beach is represented by the highest berm. Remember this is an earthcache so there is no container just an earth science lesson at a beautiful coastal natural feature. To log this cache: You should be able to see the grading of the rocks on the berm. In an email to me through my profile describe the difference between the cobble on the top and the face of the berm. Please include the name of the earthcache and the number of people in your group in your email. In your log please take the time to describe what you find special about this beach and its surrounding rocks. If you are there during low tide make sure to go out to the point to look back at the smooth shape of the pocket beach. It also would be nice if you would post a photo so others would know what they have to look forward to at this earth cache.

The Maine Geological Survey field locality "Birch Point Beach State Park, Owls Head, mid-coast Maine" at: (visit link) was used as reference.

If you enjoy this earthcache you may want to check the Maine Geological Survey located at (visit link)
They have developed a number of information sheets or field localities giving a great deal of information about geologic features. They also have a number of books and maps about Maine’s natural history/ geology that you might find interesting.

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