FAQs about the Natural History of the Inside Passage

6. How many tidewater glaciers remain in Glacier Bay? How fast are the glaciers retreating?

The glaciers seen in Glacier Bay today are remnants of the Little Ice Age that began about 4,000 years ago and reached its maximum extent in Glacier Bay around 1750, when general melting began. In 1794, Captain George Vancouver and his crew described what we now call Glacier Bay as just a small five-mile indent in a gigantic glacier that stretched to the horizon. That massive glacier was 4,000 feet thick, 20 miles wide, and extended more than 100 miles to the St. Elias mountain range. In 1879, when naturalist John Muir visited Glacier Bay, the ice had retreated more than 30 miles forming an actual bay. By 1916, the Grand Pacific Glacier, the primary glacier responsible for carving the bay, had melted back 60 miles to the head of Tarr Inlet.

Glacier Bay contains both tidewater and non-tidewater glaciers. According to the National Park Service, Glacier Bay National Park boundaries today include 11 tidewater glaciers, glaciers that flow out of the mountains and terminate in tidal waters. Eight of these tidewater glaciers flow into Glacier Bay. Many of the tidewater glaciers that Muir first observed in 1879 have been reduced to small glaciers that terminate on land.

In general, tidewater glaciers in Glacier Bay have been in a state of retreat since the 1750. However, between 1920 and 1930, the Johns Hopkins and Grand Pacific Glaciers began to advance. In 2004, the Johns Hopkins Glacier was advancing at the rate of 8 feet per day but the Grand Pacific was receding at approximately 4 feet per day. The most active tidewater glacier is McBride that is retreating at the rate of 3,000 feet per year.

Since tidewater glaciers follow their own cycles that are independent of climate changes, individual tidewater glaciers may recede, advance, or remain stable at any given time. There is one thing you can be certain—a glacier's face you see today will be changed by tomorrow and even more significantly 20 years from now.