Essay on Fritz LituyaBay 50thAnniversary Pageoph2009

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Pure appl. geophys. 166 (2009) 153–175

0033–4553/09/010153–23
DOI 10.1007/s00024-008-0435-4

Ó Birkha¨user Verlag, Basel, 2009

Pure and Applied Geophysics

Lituya Bay Landslide Impact Generated Mega-Tsunami 50th Anniversary
HERMANN M. FRITZ, FAHAD MOHAMMED, and JESEON YOO

Abstract—On July 10, 1958, an earthquake Mw 8.3 along the Fairweather fault triggered a major subaerial landslide into Gilbert Inlet at the head of Lituya Bay on the southern coast of Alaska. The landslide impacted the water at high speed generating a giant tsunami and the highest wave runup in recorded history. The megatsunami runup to an elevation of 524 m caused total forest destruction and erosion down to bedrock on a spur ridge in direct prolongation of the slide axis. A cross section of Gilbert Inlet was rebuilt at 1:675 scale in a twodimensional physical laboratory model based on the generalized Froude similarity. A pneumatic landslide tsunami generator was used to generate a high-speed granular slide with controlled impact characteristics. Stateof-the-art laser measurement techniques such as particle image velocimetry (PIV) and laser distance sensors
(LDS) were applied to the decisive initial phase with landslide impact and wave generation as well as the runup on the headland. PIV provided instantaneous velocity vector fields in a large area of interest and gave insight into kinematics of wave generation and runup. The entire process of a high-speed granular landslide impact may be subdivided into two main stages: (a) Landslide impact and penetration with flow separation, cavity formation and wave generation, and (b) air cavity collapse with landslide run-out and debris detrainment causing massive phase mixing. Formation of a large air cavity — similar to an asteroid impact — in the back of the landslide is highlighted. A three-dimenional pneumatic landslide tsunami generator was designed, constructed and successfully deployed in the tsunami wave basin at OSU. The Lituya Bay landslide was reproduced in a threedimensional physical model at 1:400 scale. The landslide surface velocities distribution was measured with PIV.
The measured tsunami amplitude and runup heights serve as benchmark for analytical and numerical models.
Key words: Tsunami, landslide, landslide generated tsunami, natural hazard, nonlinear gravity water waves, wave runup, near-field wave characteristics, slide energy conversion, three-phase flow, Alaska.

1. Introduction
Lituya Bay is a T-shaped tidal inlet that cuts through the coastal lowlands and the foothills flanking the Fairweather Range of the St. Elias Mountains on the southern coast of Alaska shown in Figure 1a. The stem corresponding to the main part of the T-shaped bay is 12 km long and extends northeastward from the bay entrance. The width of the stem ranges from 1.2 to 3.3 km except at the entrance, which is only 300 m wide. The bay fills and slightly overflows a depression carved by a valley glacier of which Lituya,
North Crillon and Cascade glaciers are remnants. Submarine contours show a pronounced

School of Civil and Environmental Engineering, Georgia Institute of Technology, 210 Technology Circle,
Savannah, GA 31407, U.S.A. E-mail: fritz@gatech.edu

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Pure appl. geophys.,

Figure 1
Lituya Bay, Alaska: (a) Overview in August 1958 (MILLER, 1960). Forest destroyed to a maximum elevation of
524 m and a maximum distance of 1100 m from high-tide shoreline at Fish Lake due to a giant tsunami generated on 10 July 1958 by a landslide at the head of the bay. (b) Map showing topographic and bathymetric contours, trace of Fairweather fault, 1958 landslide and trimline of tsunami runup (MILLER, 1960).

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Lituya Bay Landslide

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U-shaped trench with steep walls and a broad flat floor sloping gently downward from the head of the bay to a maximum depth of 220 m. Minimum depth at the entrance of the bay is 10 m. At the head of the bay the walls are fjord-like glacially over-steeped. The…