Discover the geological marvel of Bubble Rock, a highlight on the Acadia Earthcache Course, nestled atop South Bubble in Acadia National Park. As you ascend, prepare to witness a striking contrast beneath your feet and perched precariously on the cliff’s edge. Take a moment to observe the bedrock and the rounded boulder – do they appear distinct? Indeed, they are geological siblings of different origins, each telling a unique story of rock formation and glacial movement.
The bedrock you stand upon is Cadillac Mountain Granite, the very foundation of Cadillac Mountain and a signature stone throughout Acadia. However, Bubble Rock reveals a different heritage. It’s composed of Lucerne Granite, a rock type born not on Mount Desert Island, but approximately 30 miles northwest, near Lucerne, Maine. This difference in composition hints at an extraordinary journey.
Bubble Rock is a prime example of a glacial erratic, a geological term for a rock transported far from its origin by glacial ice and deposited upon a different bedrock. This 100-ton boulder, roughly the size of a minivan, embarked on an incredible journey carried by a massive glacier. Evidence of this glacial travel is etched into its very form. Notice how Bubble Rock is rounded, reminiscent of cobblestones smoothed by ocean waves along the Maine coast. This rounded appearance is a testament to the erosive power of glaciers; as the ice mass moved, sharp edges were ground away, sculpting the boulder during its long voyage. But how did this massive rock come to rest so dramatically on the cliff’s edge? As the glacier receded and melted, Bubble Rock was released from its icy grip, settling into its current gravity-defying position.
Glaciers are not only transporters of erratics but also powerful depositors of rock debris. As glaciers melt and retreat, they leave behind accumulations of boulders, stones, and till known as moraines. These moraines can act as natural dams, impounding meltwater and other water sources. A stunning example visible from the summit of South Bubble is Jordan Pond. This picturesque lake is dammed by an end moraine, formed at the glacier’s leading edge. From your vantage point at Bubble Rock, take in the panoramic view of Jordan Pond and the surrounding landscape, shaped by the immense forces of glacial activity.
