Lake Atna ( ; also known as Lake Ahtna ) was a prehistoric proglacial lake that initially formed approximately 58 ka ( thousand years ago ) in the Copper River Basin , an area roughly centered around 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
1964 Alaska earthquake
1964 Alaska earthquake
Lake Atna