Geological History of Acadia National Park

Norumbega Mountain, Acadia National Park, Maine

Norumbega Mountain, Acadia National Park, Maine (Photo credit: Wikipedia)

The formation of the landscape which we now know and love as Acadia National Park has its foundations many, many years ago. As long ago as 500 million years sand, mud and silt was transported by rivers to the floor of an ancient sea. The sediments built up around an inch every 100 years or so, which doesn’t sound like much but we’re talking millions of years here, remember, so they eventually reached depths of thousands of feet. A mixture of heat and pressure transformed the sediments into bedrock, titanic forces lift the bedrock to form a mountain range before the external forces of water, air and gravity begin grounding the mountains back again until very little remains. The rocks of the Ellsworth formation are really the only clue to the mountains of that time, long, long ago. That’s the geological history of the region of Acadia National Park in a nutshell!

These patterns kept repeating over history, and deposits which were . . . .erm . . . deposited over the Ellsworth formation became known as the Bar Harbor formation, until, around 400 million years ago (yes, we haven’t got far yet have we) volcanoes began belching out their contents . . . the ash eventually settling at the bottom off the sea. Pressure and heat transformed these deposits into the rocks which we now call the Cranberry Island formation. All of these formations, according to scientists, are “weak” rock which isn’t really fair, the rock is anything but weak, unless you’re comparing it to something like granite anyways.

Molten rock eventually invaded these “weak” rocks reshaping them, with each intrusion changing the bedrock both physically and chemically. Granite is the most common rock found in Arcadia these days.

Geological History of Acadia National Park

Time marched on, as they say, past the days when dinosaurs ruled the earth, and during these years the constant forces of erosion, rain, weathering and rivers removed the rocks which were overlying on Mount Desert. The granites which make up much of Arcadia was more erosion resistant and emerged to form an imposing mountainous ridge with stream valleys cutting through.  Just in time for the next phase in the geological history of Acadia National Park, glaciers.

 New England has been covered by giant ice sheets pretty regularly over the last two or three millions years, at least 20 or 30 times they reckon, and each new glacier significantly removes any signs of the preceding glacier, so unsurprisingly the most pronounced impact on the Acadia National Park we know and love today is from the last glacier, which was between 3,000 and 9,000 feet thick and moved from Canada across New England – that’s one pretty large glacier by anybody’s standards. As the ice reached the mountains not even the granite was able to resist the force, and even though the movement was a mere few inches, or at most a few feet each day, the strength of the force was insurmountable. As the glacier moved on so its ability to excavate valleys intensified, carving out deeper and deeper valleys. What do you think when the ice melted? Yes, you’ve got it, these deep valleys became water basins, places like Echo Lake and Eagle Lake . . . are you beginning to get the picture.

Around 18,000 years ago (wow, we’re getting closer now) the ice stopped growing, a little global warming put paid to its progress and it began to melt (where have I heard that before).  The leading edge of this glacier became the tail as it retreated and reached central Maine around 4,000 years after it first conquered the continental shelf. Great cliffs of ice broke down and released rivers from its massive bulk, as the glacier melted the sea level rose (well, all of that water had to go somewhere), but as the sea retreated the land began to rise in relation to the sea level, until it finally stabilized around 10,000 years ago.

The Shores of Acadia National Park

So let’s look at the overall picture . . . . there’s the bedrock which is the real substance of Acadia National Park, and the character which was added by the glaciers, but the awesome power of the sea has also had a real hand into shaping this dramatic landscape. Just take a look at Thunder Hole and you’ll be able to see exactly what I mean about the awesome power of the sea, when everything comes together just right, strong winds and the rising tide surging into this narrow chasm compressing the air captured within, a resounding boom can be heard, as well as felt. It’s not just the water though, the surging tides also carry stones and hurls them onto the chasm floor. The sea is not only a destructive force though, and has not only been instrument in the destruction of Acadia National Park, but also in re-building the landscape in other places. Whatever the sea carries away from one place, it deposits at another, stones and cobbles become shoals and gravel bars . . . Bar Harbor is a great example of this.

As you may have noticed, the geological history of Acadia National Park stretches back many millions of years, and can be accredited to very many things.

Acadia National Park

Acadia National Park (Photo credit: Wikipedia)


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