Giant Waves in Lituya Bay, Alaska; USGS PP 354-C

Effects of the Wave of July 9, 1958

Steven Dutch, Natural and Applied Sciences, University of Wisconsin - Green Bay
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Effects Of The Wave

Plate 3 A. View Of Lituya Bay, 1954 Trimlines of the 1936 giant waves (g) and the 1853-54 giant wave (k). Lateral moraines (m) and the end moraine in the right and left foreground record a recent advance of ice to the mouth of the bay. Mount Crillon, altitude 12,726 feet, is the highest peak on the skyline

B. View In August 1958 A giant wave generated on July 9, 1958, by a rockslide from the cliff (r) at the head of the bay destroyed the forest over the light areas to a maximum altitude of 1,720 feet at d and to a maximum distance of 3,600 feet in from the high-tide shoreline at Fish Lake (F). A fishing boat anchored in the cove at b was carried over the spit in the foreground; a boat under way near the entrance was sunk and a third boat, anchored at a rode out the wave

Destruction Of Vegetation

The trimline (upper limit of total or near total destruction by water of the forest and other vegetation) along the shores of Lituya Bay is plotted on figure 15 and is illustrated by several photographs (pls. 3B, 4B, 5A, 6B, 7 A and B). The altitude at the highest point on the trimline and at other critical points was measured by means of an altimeter that was set at mean sea level, carried up to the trimline, and read again at sea made within a period of 1 hour or less. The horizontal level. At most stations the series of three readings was position of the trimline was plotted by transferring its trace by inspection from the oblique photographs taken by the writer in 1958 to vertical photographs taken in 1948, and thence to the map of the bay. Additional altitudes were determined photogrammetrically from the 1948 vertical photographs and from the 1958 U.S. Coast and Geodetic Survey single-lens vertical photographs covering the outer mile of the bay. Prints of some 9lens photographs taken after the 1958 wave were obtained in February 1959. Since suitable photogrammetric equipment was not available, they could be used only to add details to the trimlines in areas of low relief around the outer part of the bay. A map of Lituya Bay on a scale of 1:10,000, with a 50-foot contour interval, has been compiled from the 9-lens photographs by the U.S. Coast and Geodetic Survey (H. A. Karo, written communication, Apr. 28, 1959).

The trimline formed by the 1958 wave extended to a maximum height of 1,720 feet above mean sea level, on the spur southwest of Gilbert Inlet, (pl. 4B). Its maximum horizontal distance was about 3,600 feet from the high-tide shoreline, in the vicinity of Fish Lake. Along a 1-mile segment midway between the head and entrance of the bay the band of destruction on the north and south shores averages 1,200 feet in width and extends to an average altitude of about 110 feet. The total area between the trimlines and the high-tide shorelines in the bay is about 4 square miles. This figure includes small lakes and small areas of steep slopes and beaches where little or no vegetation was growing, but it is a measure of the total area over which the wave was capable of felling a large proportion of the trees. The total area inundated by the wave is still larger, probably at least 5 square miles. \

Plate 4 A. Northeast Wall Of Gilbert Inlet, August 1958 Shows scar of rockslide. Head of slide, at about 3,000 feet altitude, was just below snowfield in upper center. Front of Lituya Glacier at lower left corner

B. View Northwest At Head Of Lituya Bay, August 1958 Large rockslide plunged into Gilbert Inlet at lower right corner, shearing off part of the front of Lituya Glacier and causing water to surge over the spur opposite. The trim line slopes down to right, across scars of slides that occurred before the 1958 earthquake

One of the most impressive aspects of the 1958 wave is the thoroughness of its destruction of the forest nearly extending to the upper limit of inundation; this can best be conveyed by photographs. In most places the trees were washed out and carried away, leaving bare ground (pl. 5A).

Plate 5 A. View west from Coal Creek, on south shore of Lituya Bay, August 1958. Trimline at left margin is at an altitude of about 180 feet, and is 1,000 feet in from the high-tide shoreline

B. Stump of living spruce tree broken off by the 1958 giant wave at Harbor Point, mouth of Lituya Bay. Brim of hat is 12 inches in diameter

In some places, mostly on steep slopes where the roots were anchored in bed- rock, the trunks were twisted or broken off just above ground level. At Harbor Point a living spruce tree was broken off cleanly about 3 feet above the root system, where it measured 4 feet in minimum diameter (pl. 5B). At a few places, mainly at the edge of the trimline, trees were pushed over but not washed out (pl. 7B, lower left). Only along the outer mile of the bay were clumps of trees left standing within the trimline. The forest was left standing to the hightide line at only two points, on the south shore 0.4 mile from the entrance and on the north shore 1.4 miles from the entrance (fig. 15). The wave's competency is shown also by the sharp trimline and by the narrow channels cut through the trees on Cenotaph Island (pl. 6A), into a small lake east of Fish Lake and into the lakes east of Harbor Point. On steeper slopes from Cenotaph Island toward the heard of the bay the water had washed into the forest generally not more than 10 to 20 feet vertically above and 30 to 100 feet horizontally beyond the trimline. On low slopes in the outer part of the bay, however, the water at some places flowed through the forest for much greater distances, probably as much as a quarter of a mile, beyond the trimline. Salt poisoning of some bushes and plants was indicated by the brown tone of the foliage just above the trimline; this was particularly noticeable on steep slopes at the head of the bay in late August. The larger trees showed no effects of the brief submergence in salty water, although the lower trunks of many trees bordering the trimlines were injured by impact with other trees felled or transported by the wave (pl. 6A).

Plate 6 A. View West On Cenotaph Island Shows channel cut through forest by the 1958 giant wave. Note injured tree standing at portal of channel, on right

B. North Shore Of Lituya Bay, August 1958 View is 2 miles from entrance, August 1958; forest as dense as that in the upper part of view formerly extended nearly to the shoreline. Width of zone of destruction by the 1958 giant wave is about 1,700 feet at right margin of photograph. Note trees with limbs and bark removed, in foreground

Plate 7 Spur Southwest of Gilbert Inlet, August 1958

A. Trees washed out and turned upslope by water at altitude of 1,720 feet. Small slides occurred on steep slope at right during the 1958 earthquake, but destruction of forest in middle and lower left part of view is due mainly to water

B. West side of spur; note washed appearance of bedrock at lower right, in contrast to slide area just below trimline at t. height of view, front bay at lower left to upper right corner, is about 1,200 feet

Many of the trees felled by the 1958 wave were reduced to bare stems, with the limbs, roots, and even the bark removed (pl. 6B. Removal of the projecting limbs and roots was due to grinding action as the trees were rotated in the turbulent water. On many of the trees, however, the cambium layer was still smooth or even slippery and showed little evidence of abrasion, suggesting that water under high pressure or moving at high velocity stripped off the bark by a process analogous to that used for peeling logs in plywood and pulpmills.

Along much of the north shore of Lituya Bay and for short distances along the south shore and on Cenotaph Island part of the felled timber is concentrated in poorly defined to well-defined windrows at variable heights above the high-tide line. The more conspicuous of the windrows are shown on figure 15. The longest continuous line of debris can be traced for about 2 miles along the north shore.

Other Effects

No attempt was made to measure accurately the amount of erosion accomplished by the 1958 wave, and probably at only a few points along the shore of the bay are measurements made or photographs taken before 1958 sufficiently detailed to allow more than a rough estimate. From the effect on the vegetation an average minimum thickness of a foot of soil almost certainly was removed over the entire area between the trimline and the shore. This alone represents a volume of more than 4 million cubic yards. Cut banks 1 to 3 feet high were seen along the trimline at some places in the bay. At the small rounded projection of the south shore, 1.7 miles east of Harbor Point (fig. 15 loc. A), the wave cut a nearly vertical cliff about 25 feet high into till and underlying stratified sand and gravel. Large areas of bedrock were newly exposed and left as bare and clean as though washed down with a hose on the spur west of Gilbert Inlet, along most of the steep south shore from Crillon Inlet to a point 1 mile west of Coal Creek, and around much of the shore of Cenotaph Island.

Marine plants attached to rocks and marine invertebrates attached to rocks or burrowed in mud or sand were largely destroyed by the wave, at least down to mean lower low water level. On Cenotaph Island and on the south shore of Lituya Bay near the entrance, where in 1952-53 barnacles and mussels almost completely covered the rocks in the intertidal zone, and many edible clams were dug, not one living shellfish was seen in August 1958. At these localities even the basal attachment plates of most of the barnacles had been removed from the rocks. The shells of clams, barnacles, and crabs were scattered along the shore above the high-tide line and a few were seen at or near the upper limit reached by the water on Cenotaph Island and at several other places in the outer half of the bay. Failure to find the remains of any fish or deep-water shells suggests that the wave had little immediate effect on the larger swimming vertebrates and did not bring up bottom-dwelling invertebrates from a depth of more than a few tens of feet. The writer had no opportunity to examine closely the forest adjoining the trimlines near the entrance of the bay, however, where the water flowed out through the trees and where stranded fish would most likely be found. Probably many bottom dwelling invertebrates in deep water were killed in place by settling of sediment eroded and transported by the wave. Some fresh-water organisms probably were also killed by the invasion of salt water into Fish Lake and smaller lakes and ponds along the shores of the bay, but these bodies of water were not examined.

Few works of man existed in Lituya Bay at the time of the 1958 wave, but judging from the effects on the vegetation and the boats, the wave would have wreaked enormous destruction on ordinary buildings and on shore structures such as docks. At the foundation sites, no trace could be found of the well-constructed cabin on the west or lee side of Cenotaph Island, used by the writer as a base camp in 1952 and 1953, or of the lighthouse mounted on concrete piers at Harbor Point. A few cut pieces of wood and some metal utensils from the cabin on Cenotaph Island were found several hundred feet from the former site.

Equipment left by a mining company at an intended campsite near the south shore was washed away (Henrickson, 1959, p. 18). Monuments marking U.S. Coast and Geodetic Survey triangulation points at Harbor Point and several other stations along the north and south shores of the bay are believed to have been washed out or moved. Station "Ice," marked by a bronze disk set in a large boulder on the shore at the head of the bay was found by the writer and apparently had not moved. Markers set in bedrock on the north and south shores just west of the two arms at the head of the bay, and one marker set in a concrete post on La Chaussee Spit seem, from study of photographs, to have remained in place also.

With regard to the destructiveness of the wave, R. L. Wiegel (written communication, Mar. 31, 1959) commented as follows

The method by which the wave broke and uprooted trees is easily explained using existing theory and data on wave-induced forces (Wiegel and Beebe, 1956; Wiegel, Beebe, and Moon, 1957) ; Wiegel and Skjei, 1958). For example, taking a conservative estimate of wave height and water depth, the total moment about the bottom of a tree 50 feet high with an effective dense crown diameter of 20 feet and trunk diameter of 2 feet was computed to be of the order of 25 million foot-pounds, which is far in excess of the conservative 300,000 foot-pounds necessary to snap the tree or uproot it (Fons and Pong, 1957).

The problem of peeling the bark off a tree is a little more difficult. It may be due to the high water particle velocities in the waves. A solitary wave 100 feet high moving in water 400 feet deep will have a horizontal component of water particle velocity in excess of 100 feet per second just under the wave crest. This, combined with the observation in the model that the wave crest along the edges of the bay moved at the same velocity as the wave in the center of the bay, indicates that a water particle velocity of this magnitude would have existed over a substantial portion of the forested slope. The shear stress on the bark due to this velocity and extreme hydraulic roughness of the bark might have been adequate to strip the bark from the trees, especially as cracks probably formed in the bark as the trees were being bent prior to breaking.

The water particle velocities along the edges of Cenotaph Island would have been great also, and this might explain the stripping of barnacles from the rocks.

The water particle velocities at the bottom of the main portion of the bay would have been much lower.

 


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