438 A. Physical Oceanography OLR (1983) 30 (6)

Observed sea surface oscillations in New Zealand harbours previously have been regarded as a re- sponse to edge waves on the continental shelf and slope, generated by atmospheric forcing and occa- sionally by tsunamis. Calculations of longshore wavelengths of the edge waves associated with the east coast continental shelf and slope suggest that Chatham Rise is part of the generation mechanism. NZOI, DSIR, P.O. Box 12-346, Wellington North, New Zealand.

83:3231 Latter, J.H., 1981. Tsunamis of volcanic origin:

summary of causes, with particular reference to Krakatoa, 1883. Bull. volcan., 44(3):467-490.

A review of known volcanic tsunamis showed that of 10 causal mechanisms, landslides are particularly dangerous because they occur suddenly without warning. By transfer of energy to sea waves, an eruption that could be harmless on land may extend destruction over a great radius. A numerical index is proposed to serve as a basis for tsunami risk contingency planning. Geophysics Div., DSIR, P.O. Box 1320, Wellington, New Zealand. (mwf)

83:3232 Lindgren, Georg and Igor Rychlik, 1982. Wave

characteristic distributions for Gaussian waves: wave-length, amplitude and steepness. Ocean Engng, 9(5):411-432.

The authors' previous approximation, which gives correct upper and lower bounds regardless of the covariance structure under Gaussian assumptions, is compared to two simpler approximations: one due to Cavani6 et al. (1976) based on a cosine process and a new one derived by replacing the model process by its regression curve. Dept. of Mathl. Statistics, Lund Inst. of Tech., Box 725, S-22007 Lund, Sweden.

83:3233 Meiron, D.I., P.G. Saffman and H.C. Yuen, 1982.

Calculation of steady three-dimensional deep- water waves. J. Fluid Mech., 124"10%121.

Steady 3-D symmetric wave patterns for finite- amplitude gravity waves on deep water are calcu- lated from the full unapproximated water-wave equations as well as from an approximate equation due to Zakharov. Solutions are obtained as bifurca- tions from plane Stokes waves. Results are in good agreement with Su's (1982) experimental observa- tions. Appl. Math., Calif. Inst. of Tech., Pasadena, Calif. 91125, USA.

83:3234 Rottman, J.W., 1982. Steep standing waves at a fluid

interface. J. Fluid Mech., 124:283-306.

An algorithm is formulated for computing pertur- bation-series solutions for standing waves on the interface between two semi-infinite fluids of dif- ferent but uniform densities. At maximum height th~ interface appears to be vertical at a point on the interface that is very near the crest for r = 10 -3 (ratio of the density of the upper fluid to that of the lower) and approaches the midpoint between crest and trough as r approaches 1.0. Dept. of Appl. Math. and Theoretical Phys., Univ. of Cambridge, Silver St., Cambridge CB3 9EW, UK.

83:32.35 Su, Ming-Yang, 1982. Three-dimensional deep-water

waves. 1. Experimental measurement of skew and symmetric wave patterns. J. Fluid Mech., 124:73- 108.

Based on observations in a tow tank and a wide basin, wave profiles, local surface slopes and amplitude spectra at various cross-sections of the crescent-shaped symmetric waves are discussed. Skew wave patterns interact between two sets of themselves propagating from different directions and are subject to Benjamin-Feir type modulations; the interactions cause compact 3-D wave packets. Agreement between experiment and theory is found for the symmetric wave patterns. Bifurcation of uniform Stokes waves into symmetric wave patterns provides a new physical process for directional energy spreading. NORDA, NSTL Station, Miss. 39529, USA.

83:3236 Su, Ming-Yang, Mark Bergin, Paul Marler and

Richard Myrick, 1982. Experiments on nonilnear instabilities and evolution of steep gravity-wave trains. J. Fluid Mech., 124:45-72.

An initial 2-D wavetrain of large steepness evolved into a series of 3-D spilling breakers, followed by a transition to a 2-D modulated wavetrain during which oblique wave groups were radiated. The final stage of evolution was a series of modulated 2-D wave groups with lower steepness and frequency. The most frequent normal modes of 2-D sub- harmonic instabilities underlying the frequency downshifting were about 4/3, 5/4 and 3/2 in terms of the ratio of fundamental to perturbed wave frequencies; timescale for the downshifting was 40-60 fundamental wave periods. Observed proces- ses have several qualitative similarities with theo- retical computations. NORDA, NSTL Station, Miss. 39529, USA.