This wave is believed to have heen higher and more damaging than the 

 first and to have reached close to the highest runup levels recorded. 

 However, as Figure 137 suggests, the main tsunami from the Continental 

 Shelf was still to arrive, although it was already making its presence 

 felt as a negative wave. We have hypothesized in Figure 137 that os- 

 cillations of period close to 12 to 15 minutes "became prevalent within 

 the first 1 1/2 hours after the earthquake. This periodicity is close 

 to the second-mode oscillation for the whole of Resurrection Bay, as 

 also the first-mode oscillation of the northern part of the "bay, acting 

 as a pseudoclosed-end basin. It is believed that the first seismic sea 

 wave arrived at about 6:30 p.m., but because of mismatched phasing, 

 failed to reach remarkable proportions . 



With the rising tide, the later tsunami waves, which were probably 

 higher because of the same kind of modulation effect as influenced the 

 Kodiak tsunami, became more dangerous. At about 10:00 p.m. a very large 

 wave surged to the head of the bay , and reached maximum uprush at about 

 30 feet above MLLW. This wave was preceded by a phenomenal drawdown 

 to ^0 feet below MLLW according to an observation of the Eads brothers 

 (Chance, I968; SEA Interview, 1966). It was also followed by a very 

 large recession which carried James Holban 1/U mile out on the tidal 

 flats (Lantz and Kirkpatrick, 196U; Chance, 1968). How this large wave 

 could have arisen is not clear except as some peculiar combination of 

 superposed waves. Afterward, and throughout the night, other big waves 

 of decreasing height surged in and out at about 1 1/k hour intervals 

 (Chance, I968). 



The waves that hit the Seward waterfront during the earthquake were 

 obviously generated by waterfront landslides or by local faulting. Not 

 so obvious is what generated the waves that hit the airport and other 

 places 8 to 10 minutes after the earthquake started. A slide at the head 

 of Thumbs Cove, shortly after the earthquake started, generated a wave 

 with a runup of UO-50 feet at the head of the cove (Lantz and Kirkpatrick, 

 196^+; Chance, I968). It is reasonable to suppose that a relatively big 

 wave also emerged from Thumbs Cove at the same time. If a part of this 

 emergent wave approached the head of Resurrection Bay, it would have 

 reached the head of the Bay within about 9 minutes. This matches well 

 with the reported time (Table VII ) that a wave rushed up the airport 

 landing strip. The Th^umbs Cove disturbance also could have triggered 

 longitudinal oscillations in Resurrection Bay, as envisioned in Figure 

 137, contributing to the violence of the second wave at 6:00 p.m. 



The exact runup along the waterfront of individual waves is unknown. 

 Maximum runup, probably caused by the wave at about 10:00 p.m., is well 

 established from eyewitness accounts and from aerial photographs taken 

 three days after the earthquake by Air Photo Tech Inc. of Anchorage. This 

 runup line has been drawn in Figure 1^+5 from inspection of vertical and 

 oblique aerial photographs and ground photographs. Postquake contours 

 of ground level and water depth are included in Figure 1U5 and prove the 

 general consistency of the runup line, which averages about 27 feet above 

 MLLW. In places the runup exceeds 30 feet, notably on either side of the 



230 



