Wrangell-St. Elias National Park

The Wrangell Mountains, which form much of Wrangell-St. Elias National Park and Preserve, are made up largely of thousands of lava flows that have erupted mostly from large, broad volcanoes during the past 26 million years. This extensive volcanic terrain, which is called the Wrangell volcanic field, covers about 4,000 square miles—an area a little smaller than the State of Connecticut—and extends eastward from the Copper River Basin through the Wrangell Mountains, into the St. Elias Mountains of Alaska and the Yukon Territory of Canada.

The Wrangell volcanoes are among the highest mountains in North America and some of the largest (by volume) in the world. In comparison to most stratovolcanoes associated with convergent plate margins, such as along the Pacific "rim of fire", the Wrangell shield volcanoes are much more voluminous. Mt. Wrangell and Mt. Sanford, for example, each consist of about 250 cubic miles of lava. Compare that to about eight cubic miles for Mt. St. Helens and 47 cubic miles for Mt. Rainier, or even Mt. Fujiyama with 184 cubic miles.

All the volcanoes of the western Wrangell Mountains are less than five million years old, with the youngest lava flows possibly as recent as 50,000 years ago. Most of volcanoes of the Western Wrangell Mountains are unlike other volcanoes located around the Pacific rim. Rather than erupting explosive lavas forming steep-sided cones, they have been built by the accumulation of hundreds of relatively fluid lava flows to form broad mountains with gentle slopes, typical of shield volcanoes. Now only youthful Mount Wrangell still displays a shield-like form; the other, generally older volcanoes have had much of their superstructure removed by glacial and other erosional processes.

More than 12 volcanic centers are known and mapped. Mounts Drum and Churchill have had explosive phases during their geologic changes.

Relatively recent eruptive activity has been noted in Mt. Wrangell in 1784, 1884-5, and 1900. On clear, cold, and calm days, steam plumes are often visible. Large volumes of ash were deposited 1,250 and 1,890 years ago from the eruption of Mt. Churchill (the White River Ash).

The principal basement rocks on which the Wrangell volcanoes erupted their great outpourings of lava are much older rocks and have had a complex geologic history. These rocks belong to what is referred to in the geologic literature as the Wrangellia terrane, which is part of an even larger group of exotic terranes—the Wrangellia composite terrane—that have been accreted to Alaska and the North American Continent over the past few hundred million years. On the basis of geophysical and fossil evidence, rocks of the Wrangellia terrane were formed in a tropical environment thousands of miles south of its present position. The Wrangellia terrane began as a volcanic arc about 300 million years ago, probably along the margin of an ancient North American Continent. As arc-related volcanic activity waned, a rift developed between the arc and continent, allowing the eruption of thousands of cubic miles of basalt lava flows that flooded and filled the rift-formed basin. Subsequently, shallow, warm seas inundated the land, depositing layers of marine limestone and other sediment on the volcanic rocks.

During the next 200 million years, the Wrangellia terrane was gradually transported northward, where it was welded to other terranes and eventually docked against western North America about 100 million years ago. It now forms a belt extending from southern Alaska to southern British Columbia. Subsequently, other terranes, such as those composing the Southern Margin composite terrane, have been carried northward and accreted to continental Alaska. The last terrane to arrive—the Yakutatterrane—docked about 26 million years ago, concurrent with and partly responsible for the development of the Wrangell volcanic field.

The basement rocks upon which the Wrangell volcanoes erupted their great outpourings of lava are much older and have had a complex geologic history. These rocks, known as the Wrangellia composite terrane, were formed at a considerably lower, warmer latitude (17 degrees) thousands of miles south of its present position and about 300 million years ago.

Essentially, the mountain ranges of interior Alaska are the result of the collision and accretion of smaller, moving tectonic plates with the North American continent.

The Malaspina Glacier flows out of the St. Elias Range between Icy Bay and Yakutat Bay in a mass larger than the State of Rhode Island. It carries so much glacial silt that plants and trees take hold on its extremities, grow to maturity, and topple over the edge as the glacier melts. Flowing from the glaciers are a multitude of meandering rivers and braided streams. The Copper River, the largest, forms the western boundary of the park starting in the Wrangells and emptying into the Gulf of Alaska in Chugach National Forest.

In the early 1900's the Kennecott Mining Co. transported copper from its mines near McCarthy by railroad along the Chitina and Copper rivers to ships at Cordova. Ore was extracted from these highly productive mines between 1911 and 1938 and lured many people to the area. During that period gold was extracted from the Nabesna area as well. Today mining still occurs on private lands within the park, and you can see evidence of earlier mining, including the ruins of the Kennecott mines, which have been placed on the National Register of Historic Places. Indian villages expanded and a number of new towns sprang up in mining's heyday. Copper Center, Chitina, Gulkana, and Chistochina are among the old Athapascin settlements. Yakutat, on the coast, is a traditional Tlingit fishing village.