page_title: Lake Atna
section_title: Remnants and effects
hierarchical_section_title: Lake Atna / Remnants and effects
caption_attribution_description: English: Looking east from w:Glenn Highway towards w:Mt. Drum, showing the Copper River Basin.
context_page_description: Lake Atna was a prehistoric proglacial lake that initially formed approximately 58 ka in the Copper River Basin, an area roughly centered around 245 km northeast of modern-day Anchorage, Alaska. The lake formed and dispersed during the Wisconsin glaciation. The lake existed in several forms, with several prominent shorelines observable in modern geology. At its greatest extent, the lake surface area was approximately half the size of modern-day Lake Ontario, and possibly much larger. The basin of the lake lay within an area bordered by the Alaska Range to the north, the Wrangell Mountains to the east, the Chugach Mountains to the south, and the Talkeetna Mountains to the west. Lake Atna may have generated several of the largest ever glacial lake outburst floods. One such flood may have contributed to the destruction caused by the 1964 Alaska earthquake.
context_section_description: Diamicton, glacial, glaciolacustrine, and lacustrine origin deposits exist in many areas of the Copper River Basin. All major rivers present today occupy narrow valleys that have cut up to 137 m (449 ft) into the bottom of the basin. Lacustrine sediments of the lake are visible in many river bluffs throughout the basin. Several extant lakes in the basin are remnants of the lake, including Tazlina Lake, Klutina Lake, and Tonsina Lake. Much of the unconsolidated fill of the basin is in permafrost, down to a maximum depth of 75 m (246 ft) in the central basin area. The postulated Matanuska Valley flood produced by Lake Atna 17,000 years ago may have been responsible for the deposition of a thin stratum of clay and silt grains in the Anchorage area. The collapse of this stratum caused catastrophic landslides in the Anchorage area during the 1964 Alaska earthquake contributing to the collapse of structures built above it.
caption: The Copper River Basin as it is now, looking east from Glenn Highway towards Mt. Drum. Lake Atna covered this basin.
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