The nature of these early waves now demands some explanation, particularly 

 in regard to the direction of the flow effects. A plausible explanation 

 for the effects might be as follows. It is supposed that the sediments 

 off the Lowe River delta and Valdez glacier outwash were much finer than 

 those found off Valdez, and that these fine sediments liquefied at an 

 early stage of the earth vibration and caused a slide in the southeast 

 corner of Port Valdez. Simultaneously the entire basin of Port Valdez 

 was being jerked horizontally to the southeast parallel to the coastline 

 of Valdez (Figure l6). The net effect of this would be to pile water to 

 the north shore near Mineral Creek (Figure l6o), and draw it from the 

 south shore. Off Valdez itself, a pseudonodal situation would arise in 

 which a flow of water would take place to the northwest without a great 

 deal of recession. This flow would have pulled the Chena to the north- 

 west; alternately, if the horizontal land thrust were sudden enough, the 

 harbor would have been pushed southeast of the Chena, which momentarily 

 remained fixed in space, with the same relative effect. 



If this suppositiort is anywhere near correct, a transverse seiche 

 would have developed, and thrown an edgewave southward along the Valdez 

 shoreline. Taking the velocity c of the edgewave as that in Equation 

 {hh) and assuming the period T of the seiche for a rectangular transverse 

 profile of width L at the head of the bay (Figure l6) to be 



T = ^ (50) 



c 



we find the period of the edgewave to be (on elimination of c between 

 Equations (UU) and (50) ) 



T = (l+irL/g sin %)^^^ (5l) 



For a bottom slope of about 1 in 11 and a width L - 2.9^ nautical miles, 

 the wave period is calculated to be 



T == U.U minutes (52) 



which could mean that the edgewave struck Valdez (midway between the 

 north and south shores of Port Valdez) within 1.1 minutes of the start 

 of the earthquake. As an edgewave it would have had the directional 

 effect to sweep the Chena southeast onto the collapsing docks, and cause 

 the extraordinary flow of water which carried away the south pier and 

 the cannery from the North Arm. 



The backlash from the edgewave would have come about U.U minutes 

 later, and presumably filled the boat harbor, freed the Chena, and caused 

 the northward flow, which may have carried small boats and debris in that 

 direction, as observed by Sturgis. 



There would then have followed the returning nodal flow in a south- 

 east direction which could account for the jetlike evacuation of the 

 Chena. The resulting suctionlike withdrawal of the water table could 

 accoiint for the sudden failure of the seabed as envisioned in Figure l67f . 



278 



