How the 524 meter tsunami led to cataclysms in Alaska

2024 Author: Seth Attwood | [email protected]. Last modified: 2023-12-16 15:55

On July 9, 1958, an unusually violent disaster struck Lituya Bay in southeastern Alaska. There was a strong earthquake at the Fairweather Fault, which caused the destruction of buildings, the collapse of the coast, the formation of numerous cracks. And a huge landslide on the side of a mountain above the bay caused a wave of a record height of 524 m, which swept at a speed of 160 km / h across the narrow, fjord-like bay.

“After the first push, I fell off my bunk and looked towards the beginning of the bay, where the noise was coming from. The mountains trembled terribly, stones and avalanches rushed down. And the glacier in the north was especially striking, it is called the Lituya glacier. Usually it is not visible from where I was at anchor. People shake their heads when I tell them that I saw him that night. I can't help it if they don't believe me. I know the glacier is not visible from where I was anchored in Anchorage Harbor, but I also know that I saw it that night. The glacier rose into the air and moved forward, so that it became visible. He must have climbed several hundred feet. I'm not saying that he just hung in the air. But he shook and jumped like crazy. Large chunks of ice fell from its surface into the water. The glacier was six miles away from me, and I saw large chunks falling off of it like a huge dump truck. This went on for some time - it's hard to say how long - and then suddenly the glacier disappeared from sight and a large wall of water rose above this place. The wave went in our direction, after which I was too busy to say what else was going on there."

Lituya is a fjord located on the Fairweather Fault in the northeastern Gulf of Alaska. It is a T-shaped bay 14 kilometers long and up to three kilometers wide. The maximum depth is 220 m. The narrow entrance to the bay is only 10 m deep. Two glaciers descend into the Lituya bay, each of which is about 19 km long and up to 1.6 km wide. Over the century preceding the described events, waves of more than 50 meters in height have already been observed in Lituya several times: in 1854, 1899 and 1936.

The 1958 earthquake caused a subaerial rockfall at the mouth of the Gilbert Glacier in Lituya Bay. As a result of this landslide, more than 30 million cubic meters of rocks collapsed into the bay and led to the formation of megatsunami. This disaster killed 5 people: three on the island of Hantaak and two more were washed away by a wave in the bay. In Yakutat, the only permanent settlement near the epicenter, infrastructure facilities were damaged: bridges, docks and oil pipelines.

After the earthquake, a study was carried out of a subglacial lake located to the northwest of the bend of the Lituya glacier at the very beginning of the bay. It turned out that the lake sank 30 meters. This fact served as the basis for yet another hypothesis of the formation of a giant wave with a height of more than 500 meters. Probably, during the glacier descent, a large volume of water entered the bay through an ice tunnel under the glacier. However, the flow of water from the lake could not be the main cause of the occurrence of megatsunami.

A huge mass of ice, rocks and earth (about 300 million cubic meters in volume) rushed down from the glacier, exposing the mountain slopes. The earthquake destroyed numerous buildings, cracks formed in the ground, and the coast slipped. The moving mass fell on the northern part of the bay, dumped it, and then crawled to the opposite side of the mountain, tearing off the forest cover from it to a height of more than three hundred meters. The landslide generated a giant wave, which literally carried the Lituya Bay towards the ocean. The wave was so great that it swept over the entire sandbank at the mouth of the bay.

The people on board the ships that anchored in the bay were eyewitnesses to the disaster. From a terrible shock, they were all thrown out of their beds. Jumping to their feet, they could not believe their eyes: the sea rose up. “Giant landslides, raising clouds of dust and snow on their way, began to run along the slopes of the mountains. Soon their attention was attracted by an absolutely fantastic sight: the mass of ice of the Lituya glacier, located far to the north and usually hidden from view by a peak that rises at the entrance to the bay, seemed to rise above the mountains and then majestically collapsed into the waters of the inner bay. It all seemed like some kind of nightmare. Before the eyes of the shocked people, a huge wave rose up, which engulfed the foot of the northern mountain. Then she rolled across the bay, stripping trees from the slopes of the mountains; falling like a water mountain on the Cenotaphia island … rolled over the highest point of the island, which rose 50 m above sea level. All this mass suddenly plunged into the waters of the cramped bay, causing a huge wave, the height of which, apparently, reached 17-35 m. Its energy was so great that the wave rushed furiously across the bay, sweeping the slopes of the mountains. In the inland basin, the shock of the wave against the shore was probably very strong. The slopes of the northern mountains, facing the bay, were bare: where a dense forest used to grow, there were now bare rocks; such a picture was observed at an altitude of up to 600 meters.

One longboat was raised high, easily carried over the sandbank and thrown into the ocean. At that moment, when the launch was carried across the sandbank, the fishermen on it saw standing trees under them. The wave literally threw people across the island into the open sea. During a nightmarish ride on a giant wave, the boat banged against trees and debris. The longboat sank, but the fishermen miraculously survived and were rescued two hours later. Of the other two launches, one safely withstood the wave, but the other sank, and the people on it disappeared without a trace.

Miller found that the trees growing on the upper edge of the exposed area, just below 600 m above the bay, were bent and broken, their fallen trunks pointing towards the top of the mountain, but the roots were not pulled out of the soil. Something pushed these trees up. The tremendous force that accomplished this could not have been anything other than the top of the giant wave that swept the mountain that July evening in 1958."

Mr. Howard J. Ulrich, on his yacht, which is called "Edrie", entered the waters of Lituya Bay at about eight in the evening and anchored at a depth of nine meters in a small cove on the south coast. Howard says that all of a sudden the yacht began to sway violently. He ran out onto the deck and saw how in the northeastern part of the bay the rocks began to move due to an earthquake and a huge block of rock began to fall into the water. About two and a half minutes after the earthquake, he heard a deafening sound from the destruction of rock.

“We saw for sure that the wave came from the direction of Gilbert Bay, just before the earthquake ended. But at first it was not a wave. At first, it looked more like an explosion, as if a glacier was breaking apart. The wave grew out of the surface of the water, at first it was almost invisible, who would have thought that then the water would rise to half a kilometer in height."

Ulrich said that he watched the entire process of the development of a wave that reached their yacht in a very short time - something like two and a half or three minutes since it was first noticed. “Since we didn't want to lose the anchor, we completely etched the anchor chain (about 72 meters) and started the engine. Halfway between the northeastern edge of Lituya Bay and Cenotaph Island, one could see a 30-meter-high wall of water that stretched from coast to coast. When the wave approached the northern part of the island, it split into two parts, but after passing through the southern part of the island, the wave again became a single whole. It was smooth, only there was a small scallop on top. When this mountain of water came to our yacht, its front was quite steep and its height was from 15 to 20 meters. Before the wave came to the place where our yacht was, we did not feel any lowering of water or other changes, except for a slight vibration that was transmitted through the water from tectonic processes that began to operate during the earthquake. As soon as the wave approached us and began to raise our yacht, the anchor chain crackled violently. The yacht was carried towards the southern coast and then, on the return course of the wave, towards the center of the bay. The top of the wave was not very wide, from 7 to 15 meters, and the trailing edge was less steep than the leading one.

As a giant wave swept past us, the surface of the water returned to its normal level, but we could observe many turbulent eddies around the yacht, as well as random waves of six meters in height, which moved from one side of the bay to the other. These waves did not form any noticeable movement of water from the mouth of the bay to its northeastern part and back."

After 25-30 minutes, the surface of the bay calmed down. Near the shores, many logs, branches and trees torn from the roots could be seen. All this rubbish drifted slowly towards the center of the Lituya Bay and towards its mouth. In fact, during the entire incident, Ulrich did not lose control of the yacht. When the Edrie approached the entrance to the bay at 11 pm, a normal current could be observed there, which is usually caused by the daily ebb of ocean water.

Other eyewitnesses to the disaster, the Svenson couple on a yacht called the Badger, entered Lituya Bay at about nine in the evening. First, their ship approached Cenotaph Island, and then returned to Anchorage Bay on the northern shore of the bay, near its mouth (see map). The Svensons anchored at a depth of about seven meters and went to sleep. William Swenson's dream was interrupted by the violent vibration of the yacht's hull. He ran to the control room and began to time what was happening. A little over a minute from the moment when William first felt the vibration, and, probably just before the very end of the earthquake, he looked towards the northeastern part of the bay, which was visible against the background of Cenotaph Island. The traveler saw something, which he initially took for the Lituya glacier, which rose into the air and began to move towards the observer. “It seemed that this mass was solid, but it jumped and swayed. In front of this block, large chunks of ice were constantly falling into the water. " After a short time, "the glacier disappeared from the field of view, and instead of it a large wave appeared in that place and went in the direction of the La Gaussi spit, exactly where our yacht was anchored." In addition, Swenson drew attention to the fact that the wave flooded the coast at a very noticeable height.

When the wave passed the Cenotaph Island, its height was about 15 meters in the center of the bay and gradually decreased near the coast. She passed the island approximately two and a half minutes after she was first noticed, and reached the yacht Badger after another eleven and a half minutes (approximately). Before the arrival of the wave, William, like Howard Ulrich, did not notice any lowering of the water level or any turbulent phenomena.

The Badger yacht, which was still at anchor, was lifted by the wave and carried towards the La Gaussi spit. At the same time, the stern of the yacht was below the crest of the wave, so that the position of the vessel resembled a surfboard. Swenson looked at that moment at the place where the trees growing on the La Gaussi spit should have been visible. At that moment they were hidden by water. William noted that there was a layer of water above the tops of the trees, equal to about twice the length of his yacht, about 25 meters. After passing the La Gaussi spit, the wave very quickly began to decline.

In the place where Svenson's yacht was anchored, the water level began to drop, and the ship hit the bottom of the bay, remaining afloat not far from the coast. 3-4 minutes after the impact, Svenson saw that the water continued to flow over the La Gaussi Spit, carrying logs and other debris of forest vegetation. He was not sure if this was not the second wave that could carry the yacht across the spit into the Gulf of Alaska. Therefore, the Svenson couple left their yacht, moving to a small boat, from which they were picked up by a fishing boat a couple of hours later.

At the time of the incident, there was a third ship in Lituya Bay. It was anchored at the entrance to the bay and was sunk by a huge wave. None of the people on board survived, presumably two were killed.

What happened on July 9, 1958? That evening, a huge rock fell into the water from a steep cliff overlooking the northeastern coast of Gilbert's Bay. The area of the collapse is marked in red on the map. The impact of an incredible mass of stones from a very high height caused an unprecedented tsunami, which wiped out all living things that were located along the entire coast of the Lituya Bay up to the La Gaussi spit. After the passage of the wave along both shores of the bay, not only vegetation, but even soil remained, there was bare rock on the surface of the coast. The damage area is shown in yellow on the map.

The numbers along the coast of the bay indicate the height above sea level of the edge of the damaged land area and roughly correspond to the height of the wave that passed here.