Geology

Violent earthquakes have been a major factor in shaping the area.

Seismic activity is common, and earthquakes continue to change the landscape. On the eastern edge of the Copper River Delta, near Kayak Island, the Pacific plate forces its way under the North American plate. There is a fragment of earth crust that is trapped between, but is being slowly jammed underneath of the continental crust. Earthquakes caused by this conflict episodically transform the landscape, elevating shore-lands, shifting landmarks, triggering landslides, and causing tsunamis.

The area is in one of the most active tectonic areas in the world, and over 35 earthquakes greater than 5.0 on the Richter scale have occurred in the last 40 years. The epicenter of the 1964 Alaska earthquake, one of the largest in recent world history at 9.2 Richter scale, was only fifty miles west of the delta. Some areas in the delta rose as much as ten feet, and some uplands nearby shifted as much as thirty-five feet southward.

Tectonic action has formed the highest coastal mountain range in the world, rising from sea level to over 18,000 feet in just 36 miles to its high point at Mt. St. Elias. Four of the fifteen highest peaks in North America are here. There are at least 12 eruptive centers around the area, including Capitol Mountain, Mt. Tanada, Mt. Fordon, and Mt. Jurvis, Regal Mountain, Mt. Bear, and Universtiy Peak. In the Copper River basin, four of the glacier-coated volcanoes dominate the view: Mt. Sanford (16,237′), Mt. Drum (12,010′), Mt. Wrangell (14,163′), and Mt. Blackburn (16,390′). Mt. Wrangell still occasionally vents hot gases and sometimes ash coats the ice-covered summit. Geothermal activity is well documented, and thermal scanning has revealed hotspots in the northern part of the Copper River watershed.

These intense tectonic interactions create ideal geology for minerals. Gold, silver, platinum, molybdenum, lead, zinc, manganese, chromate, antimony, nickel, tungsten, and copper are found here.

The Bonanza-Kennicott Copper Mine near McCarthy held some of the purest copper deposits ever exploited, and from 1911 until the mines closed in 1938 produced over $200 million of copper, gold and silver.

Oil and gas deposits are found in the North Gulf and Copper River sedimentary provinces, with surface oil seeps common in the area along the coast between Icy Bay and Katalla. In September 1902 the first commercial oil in Alaska was pumped from the ground at Katalla.

The Katalla field is located on the onshore portion of the Gulf of Alaska Territory Province. The oil is contained in the complexly faulted Poul Creek formation. Wells drilled between 1901 and 1932 varied in depth from several hundred feet to 2,300 feet. Most of the limited oil production came from wells producing from depths between 360 and 1,750 feet. In all, 44 wells were drilled, and most were dry holes, plugged and abandoned. Only 154,000 barrels of oil were pumped from the 18 producing wells over the life of the field. A small refinery at Katalla produced gasoline, diesel, kerosene and lube oil for area markets before a fire destroyed the refinery on Christmas Day in 1932. Oil production was never resumed.

In addition to Katalla exploration, 25 other exploratory wells were drilled and abandoned in the area in the 1950′s and 60′s. In off shore areas, 12 wells were drilled and abandoned between 1975 and 1983, and one abandoned attempt was made at Katalla in 1985. Attempts to find exploitable quantities of oil have been unsuccessful, and a recent specialist report on minerals by the US Forest Service rated the potential low.

In the upper Copper River Basin, 11 exploratory wells were drilled between 1957 and 1983. The deepest reached a depth of 8,840 feet. Two wells had small gas shows. One well had a minor occurrence of residual tar, an indication that oil had migrated through the area. All have been plugged and abandoned. The Alaska Department of Natural Resources reports that the oil potential is low to moderate.

Non-metallic minerals include limestone and coal. Shallow sediments in some Copper River Basin areas contain low rank coal in individual seams up to 30 feet thick, at depths of 700 to 2,000 feet. Small amounts of methane gas may be available from shallow wells. Higher-grade coal deposits are found in the Carbon mountain area near Katalla.

The Chugach and Wrangell-St.Elias Mountains are home to one of the world’s most extensive ice fields; the Bering Glacier-Beagley Icefield covers over 2,300 square miles, the most extensive in the world outside the polar ice caps and Greenland. This icefield is home to the largest surging glacier on earth.

© 2011 Copper River Knowledge System