| Icy Bay | |
| Location: | Yakutat, Alaska |
| Coordinates: | 59.99°N -141.3903°W |
| Type: | Fjord |
| Oceans: | Pacific Ocean |
| Pushpin Map: | Alaska |
| Pushpin Map Caption: | Location in Alaska |
Icy Bay (Tlingit: Lig̲aasi Áa) is a body of water in the borough of Yakutat, Alaska, formed in the last 100 years by the rapid retreat of the Guyot, Yahtse, and Tyndall Glaciers. It is part of the Wrangell-Saint Elias Wilderness.
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. A century-long glacial retreat has opened a multi-armed bay more than 30miles long.
Icy Bay is a popular destination for sea kayakers, and is reachable by bush plane from Yakutat, 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.[4] [1]
The resulting landslide generated a megatsunami in Taan Fjord. The area is uninhabited and no one was visiting it at the time, and the event went undetected for several hours until its signature was noted as a 4.9 magnitude event[2] on seismograms at Columbia University in New York City.[5]
Scientists visited the fjord in the spring and summer of 2016 to gather data on the event.[1] Their studies revealed that the landslide consisted of about 200000000ST of rock with a volume of 76000000sigfig=3NaNsigfig=3[6] and lasted 60 to 100 seconds,[1] reaching a maximum speed of 72to.[1] Some of the landslide came to rest on the foot of Tyndall Glacier,[1] [4] but about 180000000sigfig=3NaNsigfig=3 of rock with a volume of about 50000000sigfig=3NaNsigfig=3 entered the fjord,[3] [1] [6] [7] where it dislodged another 100000000sigfig=3NaNsigfig=3 of material from the bottom of the fjord.[6] Some of the landslide's debris traversed the 90m (300feet) deep water at the head of the fjord and then climbed 1050NaN0 to reach a final resting place at an elevation of about 150NaN0 on the opposite shore.[2] Altogether, the landslide debris covered 2km2.[3]
The landslide generated a megatsunami with an initial height of about 100m (300feet)[4] [8] that struck the opposite shore of the fjord, with a run-up height (i.e., the maximum height on land the megatsunami reached as it ran up the shore) of 193m (633feet).[1] [2] At a speed of up to 60mph,[7] the megatsunami then continued down the entire length of the fjord – about 15km (09miles) – and into Icy Bay.[1] In the uppermost 1.5km (00.9miles) of the fjord, run-up exceeded 1000NaN0 along the shore,[2] and run-up heights in the upper part of the fjord otherwise varied between 70and on the southeast shore and 30and on the northwest side.[1] In the middle part of the fjord, run-up heights varied greatly, dropping to as low as 3to[1] in some places but reaching 40to in others.[1] In the lower fjord, run-up heights on both sides were 15to, increasing to 20to at the entrance to the fjord.[1] Along its path, the wave inundated an overall area of 20km2[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 150feet.[7]
The wave may have been about 40feet tall[8] when it entered Icy Bay itself about 12 minutes after the landslide,[2] and it inundated the bay's coastline with run-up levels of as much as 4to in some places,[1] although the run-up diminished to below the normal high-tide level in Icy Bay at distances greater than 5km (03miles) from the mouth of Taan Fiord.[2] When it reached the nearest tide gauge, located 140abbr=off0abbr=off[1] to the southeast of the landslide near Yakutat, Alaska, the wave had diminished to a height of 15abbr=offNaNabbr=off.[1]
The Taan Fiord event bore a strong similarity to the July 1958 landslide and megatsunami in Alaska's Lituya Bay.[7] The Taan Fiord landslide was the largest recorded in North America since the eruption of Mount St. Helens in May 1980,[5] and the largest non-volcanic landslide in North America ever recorded.[9] The megatsunami was the largest known marine tsunami worldwide since the Lituya Bay wave;[10] although the Taan Fiord landslide was larger than the one at Lituya Bay, the Lituya Bay wave was larger than the one in Taan Fiord because the landslide in Taan Fiord did not fall from as great a height and landed in shallower water.[4] The Taan Fiord wave also was the fourth-largest megatsunami of any type over the previous 100 years,[7] with the fourth-highest run-up ever recorded anywhere in the world.[2] [3] Scientists assessed the landslide occurred because the 17km (11miles) retreat of Tyndall Glacier between 1961 and 1991[2] [7] had left the mountainside unsupported by what had once been about 400sigfig=2NaNsigfig=2 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 5000NaN0 away arrived two minutes before the landside began and may also have contributed to the event.[2]