To predict future coastal hazards, it is important to quantify any links between climate drivers and spatial patterns of coastal change. However, most studies of future coastal vulnerability do not account for the dynamic components of coastal water levels during storms, notably wave-driven processes, storm surges and seasonal water level anomalies, although these components can add metres to water levels during extreme events. Here we synthesize multi-decadal, co-located data assimilated between 1979 and 2012 that describe wave climate, local water levels and coastal change for 48 beaches throughout the Pacific Ocean basin. We find that observed coastal erosion across the Pacific varies most closely with El Niño/Southern Oscillation, with a smaller influence from the Southern Annular Mode and the Pacific North American pattern. In the northern and southern Pacific Ocean, regional wave and water level anomalies are significantly correlated to a suite of climate indices, particularly during boreal winter; conditions in the northeast Pacific Ocean are often opposite to those in the western and southern Pacific. We conclude that, if projections for an increasing frequency of extreme El Niño and La Niña events over the twenty-first century are confirmed, then populated regions on opposite sides of the Pacific Ocean basin could be alternately exposed to extreme coastal erosion and flooding, independent of sea-level rise

Large woody debris (LWD) and colonizing vegetation alter the sediment budgets and stability of coastal dune systems. In British Columbia, LWD on beaches consists largely of historical escape logs from the coastal logging industry. In areas with strong wind regimes and high sand supply, LWD can trap appreciable amounts of windblown sand in the backshore, which can enhance foredune development and stabilization (roles typically played by vegetation) on stable or prograding shorelines. This additional store of sediment provides an important buffer that reduces erosion of established foredunes and backshore ecosystems. This study examines trends in LWD and vegetation coverage and associated geomorphic changes within the Long Beach unit of Pacific Rim National Park Reserve derived from aerial photography since the early 1970s. Over this time LWD has been reworked seasonally to interannually and, at Wickaninnish Bay, has declined in areal coverage by 61%. Despite this decline, LWD is found extensively within established foredunes and swales in the study area. In combination with vegetation colonization, this has promoted shoreline advance rates as rapid as 1.5 m·a -1 . At Schooner Cove and Wickaninnish Beach, vegetation colonization is occurring rapidly and has reduced active sand surfaces of large, transgressive dunes landward of the foredune by~28% over the 34 year observation period. This may reflect both park protection initiatives (i.e., reduced foot and vehicular traffic) and a warming and wetter climate regime on the British Columbia coast over the study period and suggests increasing future stabilization of dune systems in the area.Résumé : D'importants débris de bois et une végétation colonisatrice altèrent les bilans sédimentaires et la stabilité des systèmes de dunes littorales. En Colombie-Britannique, ces importants débris de bois sont en général constitués de billots éga-rés provenant de l'industrie forestière de la côte. Là où les vents sont très forts et que beaucoup de sable est disponible, les débris peuvent piéger de grandes quantités de sable soufflé par le vent dans l'arrière-plage, ce qui peut encourager le déve-loppement et la stabilisation d'avant-dunes (des rôles habituellement réservés à la végétation) sur des littoraux stables ou d'accrétion. Cette réserve additionnelle de sédiments fournit un tampon important qui réduit l'érosion des avant-dunes et des écosystèmes d'arrière-plage établis. La présente étude examine les importants débris de bois et la couverture végétale ainsi que les changements géomorphologiques connexes à l'intérieur de l'unité Long Beach de la Réserve de parc national du Canada Pacifc Rim à partir de photographies aériennes depuis le début des années 1970. Durant cette période, les importants débris de bois ont été travaillés selon les saisons et les années et, à la baie Wickaninnish, leur superficie a été réduite de 61 %. Malgré cette diminution, les débris de bois se retrouvent un peu partout dans les avant-dunes et les bassières établies du secteur à l'étude. Jumelés à ...

We describe and model the evolution of a recent landslide, tsunami, outburst flood, and sediment plume in the southern Coast Mountains, British Columbia, Canada. On November 28, 2020, about 18 million m3 of rock descended 1,000 m from a steep valley wall and traveled across the toe of a glacier before entering a 0.6 km2 glacier lake and producing >100‐m high run‐up. Water overtopped the lake outlet and scoured a 10‐km long channel before depositing debris on a 2‐km2 fan below the lake outlet. Floodwater, organic debris, and fine sediment entered a fjord where it produced a 60+km long sediment plume and altered turbidity, water temperature, and water chemistry for weeks. The outburst flood destroyed forest and salmon spawning habitat. Physically based models of the landslide, tsunami, and flood provide real‐time simulations of the event and can improve understanding of similar hazard cascades and the risk they pose.

Increases in the frequency and magnitude of extreme water levels and storm surges are correlated with known indices of climatic variability (CV), including the El Niño Southern Oscillation (ENSO) and the Pacific Decadal Oscillation (PDO), along some areas of the British Columbia coast. Since a shift to a positive PDO regime in 1977, the effects of ENSO events have been more frequent, persistent, and intense. Teleconnected impacts include more frequent storms, higher surges, and enhanced coastal erosion. The response of oceanographic forcing mechanisms (i.e. tide, surge, wave height, wave period) to CV events and their role in coastal erosion remain unclear, particularly in western Canada. As a first step in exploring the interactions between ocean–atmosphere forcing and beach–dune responses, this paper assembles the historic erosive total water level (TWL) regime and explores relations with observed high magnitude storms that have occurred in the Tofino‐Ucluelet region (Wickaninnish Bay) on the west coast of Vancouver Island, British Columbia, Canada. Extreme events where TWL exceeded an erosional threshold (i.e. elevation of the beach–foredune junction) of 5·5 m aCD are examined to identify dominant forcing mechanisms and to classify a regime that describes erosive events driven principally by wave conditions (61·5%), followed by surge (21·8%), and tidal (16·7%) effects. Furthermore, teleconnections between regional CV phenomena, extreme storm events and, by association, coastal erosion, are explored. Despite regional sea level rise (eustatic and steric), rapid crustal uplift rates have resulted in a falling relative sea level and, in some sedimentary systems, shoreline progradation at rates approaching +1·5 m a–1 over recent decades. Foredune erosion occurs locally with a recurrence interval of approximately 1·53 years followed by rapid rebuilding due to high onshore sand supply and often in the presence of large woody debris and rapidly colonizing vegetation in the backshore. Copyright © 2012 John Wiley & Sons, Ltd.

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