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Eagle's Roost Park

Location #1

Location #1



Welcome to the first stop on the Naturalist’s Tour. From here at Eagle’s Roost Park, you can see Kupreanof Island and Petersburg Mountain on the other side of the Wrangell Narrows. You are currently standing on Mitkof Island. Small bodies of water like the Wrangell Narrows are part of a network of fjords, inlets, and channels that wind among Southeast Alaska’s mountainous islands. This archipelago was shaped by a tumultuous geologic past. Here in Southeast Alaska, the tectonic plate underlying the Pacific Ocean is moving northeastward, crashing into and sinking beneath the continental North American plate. This motion is by no means smooth or straight. First, the Pacific plate lifts up the North American plate before sinking entirely, raising up an impressive mountain range. Second, the overlying continental plate is shearing off chunks of the plates as they sink. These different chunks, or “terranes”, adhere to the edge of the continental plate. An eagle flying from the Canadian border west to the open ocean off Sitka will pass over five different terranes, each formed at a different time and under different conditions. Some of these terranes were formed when volcanos erupted, while others contain fossils of tropical sea life that lived 210 million years ago. Rocks in the terrain just to the west of here in Duncan Canal were originally located in the Arctic and travelled as far south as Washington before sliding back north to Southeast Alaska. Most of what you see in front of you is in the Gravina terrane, which is made up of shale and dark sandstone that was once the floor of a deep ocean basin. Now look away from town along the road and up toward the horizon. On most days, you’ll see the Coast Range Mountains rising across a large body of water known as Frederick Sound. The sheer cliffs of Devils Thumb feature prominently in this view. Why are the Coast Range Mountains jagged and bare while Petersburg Mountain is more softly rounded? The answer illustrates the power of water in its frozen form. During the last ice age, glaciers completely covered the lower mountains, smoothing their edges as they flowed southward, and carving out fjords at the same time. But the Coast Range Mountains remained above the height of the glaciers, and maintained their steep cliffs and sharp ridges. Before we continue walking, take a minute to imagine this entire area covered by ice over 3500 (thirty-five hundred) feet thick, higher than Petersburg Mountain.


Devils Thumb

Devils Thumb,
The Guardian of Frederick Sound,
has just now decided to flirt.
The shawl of snow worn low on her shoulders
reflects the sun stealing through the clouds,
and winks off her southern face;
An invitation to test the waves below.

Directions to next location

Now continue along North Nordic Drive, descending the hill until you reach the intersection with Baltic Road. Stop there and take a look onto the Wrangell Narrows.

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