Geology and Ecology of National Parks

Acadia National Park

Cadillac Mountains

A panorama of the summit of Cadillac Mountain. At 1,528 feet in elevation, Cadillac Mountain is the highest point in Acadia National Park, and is composed of a unique granite, the Cadillac Mountain granite unit.

(Credit: Alex Demas, USGS. Public domain.)

Acadia National Park, Maine’s only national park, is well known for its autumn foliage, sunrises (one of the earliest places in the US to catch the sunrise), and its rocky, pink granite rugged coastline. The park attracts 3.5 million visitors annually, making it one of the top ten most visited national park in the United States. Acadia is located in an area which has been subjected to hundreds of millions of years of geologic activity, including more recent glacial activity and coastal erosion.

Sunrise over Cadillac Mountain.

Sunrise over Cadillac Mountain.

(Credit: Kristi Rugg, NPS. Public domain.)

Over 500 million years ago, pressure beneath ancient oceans and heat from tectonic activity turned a mixture of underwater sedimentary rocks (mudstone and sandstone) and volcanic ash into the metamorphic rocks of the Ellsworth Schist, the oldest rock unit in the Mount Desert region. The Ellsworth Schist, identifiable by its green chlorite bands and white-gray quartz and feldspar bands, was exposed approximately 450 million years ago when a micro-terrane (mini-continent) called Avalonia slowly collided with North America. The Ellsworth Schist was left in a position which allowed sand and silt to accumulate on top of it. Eventually this accumulation hardened to become the Bar Harbor Formation, which today is visible as layers of sandstone and siltstone ranging in color from brown to grey. Layers of ash were deposited in the Bar Harbor Formation from nearby volcanoes (Cranberry Island Volcanics). Molten rock below Earth’s surface (magma), later intruded into this area, forming the igneous rocks (granites) of the Mount Desert Island as it cooled. The Cadillac Mountain Granite is amongst the largest bodies of granite on the island, and it is also one of the oldest in the region (~420 million years old).

 

Younger, dark-colored igneous dikes (diabase) cuts across lighter-colored intrusive igneous rock (granite).

Younger, dark-colored igneous dikes (diabase) cuts across lighter-colored intrusive igneous rock (granite).

(Credit: Georgia Hybels, NPS. Public domain.)

During the last two to three million years, thick glaciers flowed across the state of Maine, eroding mountains and carving valleys into the land across which they flowed. This activity peaked about 18,000 years ago during a period called the Wisconsin Glaciation. As large masses of ice (glaciers) receded, their bulldozer-like erosive power left scratches in the rocks called “striations” and gouges called “crescentic gouges.”

As the Earth warmed, the glaciers began to melt. As they melted, they deposited materials they had been scraping up and carrying along their journey. This left piles of rock, gravel, and sand in the wake of the melting glaciers, many of which are still present in Acadia National Park today.

Jordan Pond, a lake in Acadia National Park formed by glacial activity.

Jordan Pond, a lake in Acadia National Park formed by glacial activity. 

(Credit: Rebecca Lloyd, USGS. Public domain.)

Further changes to the land occurred around Acadia where heavy glacial ice created indentations in the land which allowed the Atlantic to flow inland once glaciers began melting. As the ocean flowed inland, mountains became islands and marine material covered what had been dry land. As the ice retreated further, the land around Acadia stabilized, rose up, and once again settled above sea level. Lakes and rivers remained in the valleys and the land became dry enough for animal habitation. Plants and animals began to recolonize what had previously been underwater.

Today, Mount Desert Island is home to 18 mountain summits and the highest cliffs on the Atlantic coast north of Rio de Janiero, as well as a population of over 10,000 people. Lakes and ponds are abundant within the park, including several large (>10 acres) ponds, known as Great Ponds.

Acadia is home to many lakes and ponds.

Acadia is home to many lakes and ponds.

(Credit: Cynthia Cullinane. Public domain.)

Acadia is also home to several miles of beaches. Each beach is composed of unique material, shaped by geological history and the strong force of the waves. Tidal valleys, protected from the brute force of ocean waves, are home to salt marshes while rocky headlands are battered by powerful waves from the Atlantic Ocean. Beaches such as Sand Beach, which are not subject to forceful wave action, are made up of fine-grained sand. Sand Beach is the longest continuous sand beach in the park and is located at the end of a cove between two headlands (Great Head and Otter Cliffs). The rock formation commonly known as “Old Soaker” is located near the center of the mouth of the cove between the headland points, adding further protection from the Atlantic Ocean waves. Much of Acadia’s coast is tectonically young and has only been subject to a limited geologic period of wave action, making sandy beaches quite rare. Less-sheltered beaches, particularly those facing the open ocean, are subject to strong wave action which removes fine-grained sand and deposits pebbles, cobbles, and even boulders along the rocky shores.

Not all beaches in Acadia National Park are composed of granite.

Not all beaches in Acadia National Park are composed of granite.

(Credit: Cynthia Cullinane. Public domain.)

Ecology of Acadia National Park

 

Acadia National Park is located in the transition zone between two ecosystems: northern boreal forest and eastern deciduous forest. Northern boreal forests, found primarily north of Acadia in Canada, are dominated by conifers. Eastern deciduous forests, which dominate the American east coast, are characterized by broad-leaf trees which shed their leaves in autumn and tend to be located in places which have four distinct seasons each year. This makes for an interesting ecological mix throughout the park and enables the presence of species common both in northern and southern regions.

Acadia National Park contains both coniferous trees (which generally don’t lose their leaves/needles in the autumn) and deciduous trees (which generally shed their leaves). Spruce-fir forests are most common throughout Acadia, but oak, maple, beech, and other New England hardwoods are plentiful in the area as well. Isolated communities of trees from farther north or south can also be found here. Pitch pine and scrub oak woodlands reach their northeastern range limit within Acadia, and jack pine reaches its southern limit.

Thousands of feet in the air, plants on Acadia’s mountain peaks are well-adapted to the cold. Spruce and pitch pine thrive in the low mountain temperatures, while subalpine plants blossom amongst cracks in the granite and on the leeward side of rocks. Gnarled, stunted trees tend to be the only ones found on open ridges on mountain peaks, which bear the brunt of the harsh Maine weather.

Wintertime in Acadia National Park.

Wintertime in Acadia National Park.

(Credit: Cynthia Cullinane. Public domain.)

Far below its mountain peaks, Acadia is also home to a very different type of habitat: wetlands. Wetlands, which comprise over 20% of the park, provide a rich ecosystem for numerous plant and animal species. Each wetland in Acadia is home to at least one rare species of plant, and more than half of the species classified as “rare” within Maine are indigenous to wetlands. These plants provide critical food and shelter for species which live in the park year-round, as well as those which pass through Acadia during migration. Acadia is home to both mineral soil and organic soil wetlands, allowing a diverse range of plants and animals to grow in these critical, delicate, areas. Closer to the coast, intertidal and subtidal zones characterize Acadia’s shoreline. Tidal pools, left behind as the ocean recedes with each low tide, are populated by sea cucumbers, rockweed, sea stars, dog whelks, mussels, and more.

Loons are large, deep-diving water birds with a unique call, and are some of Acadia’s most iconic residents. They build their nests along the edges of small ponds, often close to areas where humans enjoy swimming, kayaking, and walking their dogs. Acadia is also home to amphibians and reptiles, including snapping turtles and painted turtles.

A loon attends to its nest among the reeds.

A loon attends to its nest among the reeds.

(Credit: Cynthia Cullinane. Public domain.)

A turtle hatching emerges from the sand.

A turtle hatching emerges from the sand.

(Credit: Cynthia Cullinane. Public domain.)

Non-native species pose a direct threat to native species, who must compete with invasive species for food, water, sunlight, and other critical resources. Nearly one third of the park’s flora is non-native, and the National Parks Service currently categorizes the spread of 12 non-native species throughout the park as being of “high management concern.” To combat the encroachment of non-native species, officials in Acadia employ an integrated pest management strategy which relies upon an understanding of the invasive species’ biology and prioritizes the use of the least toxic treatments possible.

Fire is also an important factor in Acadia’s natural history. A large fire in 1947 burned most of the eastern side of Mount Desert Island is the most recent extensive fire Post-fire aspen-birch communities are still abundant. The spruce-fir forests, the dominant closed-canopy forest type on the island, include a large earlier-successional birch and red maple within the area that burned, along with the maturing spruce and fir. Vegetation on the western half of the island, which escaped the 1947 fire, reflects more clearly the underlying characteristics rather than the effects of recent fire.

Scientists supported by the USGS Northeast Climate Adaptation Science Center study a wide range of topics in the northeastern United States, including how climate may impact wildlife health, water quality and quantity, and ecosystems. Additionally, the USGS has been working with the National Park Service and other agencies to provide comprehensive maps of vegetation in several national parks, including Acadia. Learn more about that project here.

A lake in Acadia National Park.

A lake in Acadia National Park.

(Credit: Cynthia Cullinane. Public domain.)

Additional resources:

https://www.usgs.gov/media/images/jordan-pond-acadia-national-park

https://pubs.usgs.gov/sir/2014/5123/

https://www.usgs.gov/centers/water-dashboard/surface?state=me

https://www.nps.gov/acad/index.htm