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Little Hunter's Beach

Introduction

Little Hunter’s Beach is located on the south-eastern coast of Mount Desert Island (MDI). Its shore is covered in large cobbles and boulders. There’s a small waterfall leading into a stream that runs into the ocean. It’s a great place to go tide pooling and searching for beach arachnids and large seabirds. But be careful and proceed with caution! This beach is also home to slimy marine algae and other slippery organisms.

Field Site Location in Relation to Bar Harbor

Key
Little Hunter's Beach
Bar Harbor
North
Parking
North
North

Geologic History

Little Hunter’s Beach is a bed of cobble framed by two large outcrops of shatter zone. This rock type is less commonly found on the island as it forms a semicircle cutting through the left side and bordering the coastline to the right (Gilman and Chapman, 1988).  The Shatter zone can be seen on the geologic bedrock map at the bottom of this page referenced as Dsz. This formation occurred around 420 million years ago at the time of heightened volcanic activity on Mount Desert Island. As the volcanic caldera was in the process of forming Cadillac Mountain granite (Dcg), energy was forced into the cooling magma from intrusions of gabbro and diorite. This caused the rock on top and around the chamber to shatter creating the shatter zone formation. This rock is comprised of country rock suspended in Cadillac Mountain Granite. At Little Hunter’s Beach, the clasts are mostly Bar Harbor Formation (SDbh) as this is the country rock of the southeastern side of the granite chamber (Braun and Braun, 2016). Bar Harbor Formation is a metasedimentary rock which formed about 465 mya and can be found mainly on the North Eastern coast (Braun and Braun, 2016).

The beach itself is home to rounded cobble, mostly made up of Cadillac Granite and shatter zone. This was formed in response to the sea level dropping with the recession of the last glacier around 20,000 years ago. The Presumpscot Formation of marine mud covering the end of the beach is evidence of glacial activity. At the base of the shatter zone outcrops, the rock is lower to the ground and appears to be much smoother. Hummocky potholes are the result of water erosion (Braun and Braun, 2016).

Shatter Zone:
The Shatter Zone (Dsz on the bedrock map) is made up of angular and rounded blocks of siltstone suspended in a granite matrix. In these pictures the inclusions are part of the Bar Harbor Formation (SDbh on the bedrock map). The Bar Harbor Formation is a meta-siltstone about 465ma (Braun and Braun, 2016).

“This is like living life on the edge!”

- Sarah and Anna (about standing on the Shatter Zone)

Eroded Basalt Dike Partially Carved by Pebbles in a High Energy Level Environment

​The grey rock in this picture is a basalt dike that we think cuts through the Shatter Zone. This would mean that the dike is younger than the Shatter Zone according to the law of cross cutting relationships. We tried to find the contact but it was buried under too much sediment. Basalt is a common igneous rock found around MDI as dikes and along most of the ocean floor.

 

Smooth, hummocky potholes from wave erosion - The movement of water, pebbles and sand can cause erosion to form potholes and depressions in the rock. These potholes are commonly seen around the island’s coast.

Bed Rock Geology of Mount Desert Island

Fracture Sets at Little Hunter's Beach:

Fracture Set 1

190, 180, 185, 188

Average: 189

Fracture Set 2

110, 105, 105, 100

Average: 105

Fracture Set 3

346, 345, 344, 343

Average: 345

Fractures are cracks in the bedrock caused by stress. If one were to measure all the fractures on the island they would find that there are more fractures trending certain directions than others. Fractures are important because they create habitats for animals like barnacles and birds. They also provide nice surfaces for climbers and inform the development of tide pools. In the case of Little Hunter's Beach, the fractures were a part of the shatter zone, which can be seen on the geologic bedrock map to the left.

Modified after Gilman and Chapman 1988.

Little Hunter's Beach

References:

Braun, D., Braun, R., 2016, Guide to the Geology of MDI and Acadia National Park: Berkeley, California, North Atlantic Books.

Gilman, R.A., and Chapman, C.A., 1988, Bedrock Geology of Mount Desert Island, A Visitor’s    Guide to the Geology of Acadia National Park: Maine Geological Survey Department of Conservation, Bulletin 38, scale 1:50,000.

Marvinney, Robert, Earth Shattering Events at Mount Desert Island!: Maine Geological Survey, 2010.

Page Written and Designed by Anna Capitano and Sarah Somes
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