At the beginning of the 20th century, the bay entrance was permanently blocked by a giant tidewater glacier face that calved icebergs directly into the Gulf of Alaska.

At 8:19 p.m. Alaska Daylight Time on October 17, 2015, the side of a mountain collapsed on the western end of the head of Taan Fiord,[1][2][3] a finger of Icy Bay formed by the retreat of Tyndall Glacier.

[1] Along its path, the wave inundated an overall area of 20 square kilometers (7.7 sq mi)[3] and left a trim line at its run-up height, stripping away all vegetation, including alder forests, and leaving behind barren beaches that reached elevations of 150 feet (46 m).

[2] When it reached the nearest tide gauge, located 140 kilometers (87 miles)[1] to the southeast of the landslide near Yakutat, Alaska, the wave had diminished to a height of 15 centimeters (5.9 inches).

[2][3] Scientists assessed the landslide occurred because the 17-kilometer (11-mile) retreat of Tyndall Glacier between 1961 and 1991[2][7] had left the mountainside unsupported by what had once been about 400 meters (1,300 ft) of glacial ice.

[2][10] They also noted that heavy rains may have weakened the mountainside further,[2][4] and that seismic waves from a 4.1-magnitude earthquake centered about 500 kilometers (311 mi) away arrived two minutes before the landside began and may also have contributed to the event.