Bianca Massacci
Katie McConaghy
Witch Hole Pond
Bianca Massacci
Katie McConaghy
Fig. 1. Witch Hole Pond. Photo by Katie McConaghy.
Mount Desert Island
Witch Hole Pond is located in Acadia National Park, close to College of the Atlantic. The popular Duck Brook carriage roads surround part of the pond as well as several near bodies of water. Biking or running around the ponds is a favorite pastime of both locals and tourists as there is beautiful scenery. In fact, even President Obama himself went cycling along the carriage roads (Sonmez 2010).
(Left) Fig. 2. Close up of Cadillac Mountain granite. Photo by Bianca Massacci.
Witch Hole Pond’s bedrock is composed of the Cadillac Mountain Granite (fig. 2), an intrusive, felsic, igneous rock. It is the dominant rock type on Mount Desert Island, formed about 420 million years ago as a result of a cooling magma chamber that intruded into the Ellsworth Schist and the Bar Harbor Formation (Braun and Braun, 2016).
The granite (fig. 2) is composed of:
Quartz = white color
Hornblende = black color
Potassium feldspar = pink color
At field site 7 (fig. 4) we spotted a dike intruding the granite. The dike, which is about 1 foot wide (fig. 3), is made of basalt, an aphanitic (very fine grained), mafic rock, rich in magnesium and iron. This extrusive igneous rocks was formed when the volcano of MDI erupted. The lava cooled quickly, in a matter of days to weeks, which is the reason why the basalt has such small grains.
(Right) Fig. 3. Basalt dike intruding into Cadillac Mountain Granite. Photo by Katie McConaghy.
Witch Hole Pond Bedrock Units
We measured 12 fracture sets in the entire area and found that there are two main orientation trends, one going NW-SE and the other NE-SW. The orientation of the dike corresponds to the NW-SE fracture set (fig. 5), which means that the basalt dike intruded into a preexisting fracture in the granite. This fracture set orientation is similar to the one of the adjacent coastline to the east of Witch Hole Pond, as well as that of small valleys and ridges surrounding it (fig 4). This shows how fractures affect geomorphology, the shape of the land related to its geology.
Witch Hole Pond
Latitude: 44°24'0.40"N
Longitude: 68°14'34.00"W
343°
343°
67°
Trends of fracture
orientations
Dike average orientation
343°
Fig. 4. Witch Hole Pond LiDAR map with bedrock units. Red crosses indicate field sites. Purple arrows indicate the orientation of one of the fracture sets. Bedrock units after Gilman et al. (1988). Created by Bianca Massacci.
Fig. 5. Dike and fracture orientations. The average orientation of the dike is the same as the average orientation of one of the fracture sets we found. Created by Katie McConaghy.
References:
Braun, Duane D., and Ruth Braun. Guide to the Geology of Mount Desert Island and Acadia National Park. Berkeley, CA: North Atlantic, 2016. Print.
Gilman, R.A., Chapman, C.A., Lowell, T.V., and Jr., Borns, H.W., 1988, The Geology of Mount Desert Island: A Visitor’s Guide to the Geology of Acadia National Park, Maine Geological Survey Department of Conservation: http://www.maine.gov/dacf/mgs/explore/bedrock/acadia/ B-38.pdf (accessed October 2016).
Sonmez, Felicia. "An Active First Family Is on the Move in Maine." Washington Post. The Washington Post, 18 July 2010. Web. 06 Nov. 2016.