Geology
A study of the geology (landforms, rocks and minerals) of the Tongass and Chugach National Forests is foundational to our understanding of the forests. Geology reveals the history of the earth, including the landforms, rocks and minerals so prominent on the Tongass and Chugach. The surface and subsurface minerals provide valuable commodities for human use. Extraction of those minerals is not only significant today, but has been an integral activity in the history and development of both forests. Broken down, as components of soil, these minerals also provide basic nutrients and elements for forest plants and animals.
Geology in Action
Described as “rivers of ice,” glaciers have carved much of the landscape of Alaska. Massive in size, spectacular in appearance, glaciers are prominent features on the Tongass and Chugach National Forests. No study of Alaska’s National Forests would be complete without a study of glaciers.
- Alaska’s Glaciers- The Alaska Centers, present information about Alaska’s public lands, including geomorphic features such as glaciers.
- Glacier Research: The US Geological Survey has studied many glaciers, including Portage Glacier and Columbia Glacier to track their patterns of movement. To learn about specific glaciers, a simple internet search of "USGS (insert the name) Glacier" will lead you to research about that glacier.
- Hubbard Glacier - has attracted national attention in recent years for its dramatic surges forward. In 1986 and 2002, the terminal moraine of the glacier almost completely blocked the connection between Russell Fiord and Disenchantment Bay, causing Russell Fiord to become a lake. Subsequently the water pressure behind the outlet burst through the glacial ice dam, lowering the water levels back to normal.
- Mendenhall Glacier (Tlingit: Áakʼw Tʼáak Sítʼ) - just outside Juneau in the Tongass National Forest, the 13.6 miles (21.9 km) long glacier has been retreating due to increasing temperatures.
Since the acquisition of Alaska from Russia in 1867, prospectors and miners have flooded north to seek their fortune, and most came through Southeast Alaska in their quest. Over the next 100 years or so, mining activities waxed and waned with the prevailing territorial and early statehood economic and political environments. But for the last 30 years, significant increases in commodity prices as well as the development of modern transportation and mining technologies to prospect and explore for and extract mineral resources have fueled renewed interest.
The 17-million acre Tongass National Forest is endowed with tremendous potential for the development of base (copper, lead, zinc) and precious (silver, gold, and platinum) metal mines. Today the Tongass administers the only two large mining operations (250+ employees) in Southeast Alaska, both based out of Juneau. The Kensington gold mine is on the Berners Peninsula about 45 miles northwest of Juneau, and the Greens Creek Mine (silver, zinc, lead & gold) is on Admiralty Island about 25 miles to the southwest. Several other mineral properties are in various stages of exploration throughout the Tongass.
The 5.6-million acre Chugach National Forest is endowed with the potential for the development of both lode and placer deposits. Placer gold mining has been of interest on the Chugach since the Russian Era (1848), when they prospected the Kenai Peninsula for the yellow metal. What they found was obviously not enough to keep them from selling Alaska to the Americans in 1867. But, 40 years later in the late 1880’s, gold was discovered on Resurrection Creek, and the rush was on! Many miners from the Cassiar and Klondike gold strikes were in the area and all the gold-bearing creeks on the Kenai were quickly claimed. Over the years, pick and shovel placer mining using simple wooden sluice boxes gave way to more efficient hydraulic methods, and by the 1920’s the profitable deposits were cleaned out. While most of the placer resource has been mined out, the Chugach still has the potential for small-scale placer gold mining, particularly though use of small suction dredges. The placer deposits led to the discovery of significant lode deposits of base (copper, lead, & zinc) and precious (gold & silver) metals, which were mined from large operations on several locations on the forest (1904 on Latouche Island through the late 1930’s). Wars, commodity prices, and economics (more easily mined deposits in the western US and overseas) closed the lode mines of Prince William Sound, but considerable potential exists for future reevaluations. The Chugach National Forest also has great potential for the development of common variety or salable minerals (sand & gravel, shot rock, rip-rap, building stone, etc.). Growth and sprawl of the greater Anchorage bowl area is creating great demand for such resources and the forest has some strategically located reserves - most notably, the Portage Valley on the Seward Highway, and the Spencer Glacier outwash plain along the Alaska Railroad
This education document was written by a group of scientists within and outside the Forest Service and published by the Forest Service. It is designed for use by middle and secondary school teachers. It is presented here in three sections for easier downloading:
El Capitan Cave Management Plan
The cave is located on north Prince of Wales Island, within the Thome Bay Ranger District, part of the Ketchikan Area of the Tongass National Forest. The cave is a large maze-like system, over 400 feet in depth with areas still not mapped.
A geological time scale, cool features on the top fossil finds, and a map of fossil areas.
A guide to recreational gold panning on the Kenai Peninsula of the Chugach National Forest.
Other Alaska Resources
- Alaska Department of Natural Resources, Division of Geological and Geophysical Surveys - This website discusses Alaska-specific information about geophysics, mineral and energy resources, vulcanology, seismology, and more.
- Alaska Geology Information- A collection of links pertaining to geology, minerals, and land records in Alaska. Five land and natural resource agencies in Alaska contribute information.
- Alaska State Museum's "Alaska Gold" website - gives a good overview of the important role the search for gold played in the history of Alaska. Many communities on or near the Tongass and Chugach National Forests began as gold rush camps.