Pacific Northwest Littoral Data

This document contains five data tables in PDF file formats, that are used to characterize littoral subcell (beach, river mouth, and inner-shelf) conditions in the Pacific Northwest (PNW) region (Washington, Oregon, and Northern California). These data have been compiled from pre-existing data sets (see citations in Table notes and References, below) for the purposes of predicting possible beach erosion from potential future sea level rise (SLR), as introduced in Kingen (2018) and Peterson et al. (2019, 2020a,b). The five data tables include Heavy-mineral tracers (Table 1), Heavy-mineral data (normalized) (Table 2), Subcell beach profile settings (Table 3), Subcell beach profile parameters (Table 4), and Subcell shelf profile parameters (Table 5). Parts of the Heavy-mineral data (Tables 1 and 2) have been used in Peterson et al. (1984a,b; 2009; 2010; 2016; and 2020b). Detailed motivation, methods and applications for the compiled data in Tables 1 and 2 are provided in Peterson et al. (2020b). Parts of the beach profile data (Tables 3 and 4) have been used in Peterson et al. (2020b). Detailed motivation, methods and applications for the compiled data in Tables 3 and 4 are provided in Peterson et al. (2020b). Parts of the inner-shelf profile data (Table 5) have been used in Peterson et al. (2020b). Detailed motivation, methods and applications for the compiled data in Table 5 are provided in Peterson et al. (2020b). Future work on predicted SLR in the PNW region could benefit from data presented in this Documen

Estimating Sand Loss: Using Eolian Sand Ramps as a Proxy for Estimating Past Erosion within the Lincoln City Dune Sheet; Lincoln City, Oregon

Eolian sand ramps are features that are sculpted from beach sand blowing up against sea cliffs or bluffs. In some coastal areas, sand ramp deposits only appear as the erosional remnants of pre-existing ramps that have been truncated at eroded shorelines, separating them from their previous sediment supply. Although sand ramp features have been observed in other areas on the western coast of the United States , they had not been studied or documented within the Lincoln City Dune Sheet (LINC) prior to this study – which documents the existence of truncated eolian sand ramps in LINC and uses them to estimate both a volume and rate of erosion since their initial deposition. The eroded volume was estimated to be 1.17X106 ± 4.4X105 m3; based on cross-sectional sand ramp areas calculated using the height of the eroded sea cliff, the slope of the sea cliff, the mid-beach slope, and an estimated pre-erosional sand ramp slope. Using radiometric dating, the beginning of sand ramp deposition was dated as 1,160 calBP. Given that erosion must have occurred some time after the onset of deposition, this date was used to create as average rate of erosion of 1.47X103 ± 3.78X102 m3/yr, or 1.47X106 ± 3.78X105 m3 per m of sea level rise (SLR), given 1 m SLR per ka for the last 3 ka within LINC

Catastrophic Beach Sand Losses Due to Erosion from Predicted Future Sea Level Rise (0.5–1.0 m), Based on Increasing Submarine Accommodation Spaces in the High-Wave-Energy Coast of the Pacific Northwest, Washington, Oregon, and Northern California, USA

The U.S. Pacific Northwest (PNW) coastline (1000 km) has been analyzed for conditions that could impact beach erosion from potential near-future (100 year) sea level rise (SLR). Heavy mineral analysis of river, beach, and shelf samples (n = 105) establish the sources of the beach deposits. River bedload discharge and intervening estuarine sinks for river sand supplies (n = 31) were normalized to the one century time interval. Twenty-six subcell beaches (657 km in combined length) were surveyed (153 profiles) for beach sand widths (20–412 m) and sand cross-sectional areas (20–1810 m2 ) above wave-cut platforms and/or 0 m tidal datum. Cross-sectional areas were multiplied by beach segments to yield subcell beach sand volumes (0.4 × 106 m3 –35.8 × 106 m3 ± 20% uncertainty). Innermost-shelf profiles were measured for distance to the 100-year depth of closure (30 m) to digitize the areas of inner-shelf accommodation space. Both innermost-shelf and estuarine accommodation space volumes for beach sand displacements were established for 0.5 and 1.0 m SLR. The existing subcell beach sand volumes and computed new beach sand supplies (rivers and longshore transport) were subtracted from the estimated sand volumes lost to submarine accommodation spaces to establish potential beach sand deficits from near-future SLR. Of the 26 surveyed active-beaches, some 60% and 80% (by length) are predicted to be lost, respectively, from the 0.5 m and 1.0 m SLR or equivalent littoral sand sedimentation in submarine accommodation spaces. Projected losses reach 90% for all PNW beaches (~900 km total length) from 1.0 m SLR. The computed beach sand deficits are used to estimate soft-sand retreat distances or erosional beach step backs (50–590 m ± 35% uncertainty) in unrevetted barrier spit and beach/dune deflation plains from 1.0 m SLR. Such empirical accommodation space analyses should have worldwide relevance to predicting beach erosion from near-future SLR

Predicted Responses of Beaches, Bays, and Inner-Shelf Sand Supplies to Potential Sea Level Rise (0.5-1.0 m) in Three Small Littoral Subcells in the High-Wave-Energy Northern Oregon Coast, USA

Three small subcells (Nehalem, Tillamook, and Netarts) totaling ~55 km shoreline length in the high-wave energy northern Oregon coast are evaluated for potential beach sand loss from sea level rise (SLR) of 0.5–1.0 m during the next century. The predicted erosion is based on beach sand displacement from the narrow beaches (average ~120 m width) to increased submarine accommodation spaces in the innermost-shelf (to 30 m water depth) and in the subcell estuaries (Tillamook Bay, Netarts Bay, and Nehalem Bay), following predicted near-future SLR. Beach sand sources from local rivers, paleo-shelf deposits, and/or sea cliff retreat are discriminated by distinctive heavy-mineral tracers. Modern beach sands in the study area are derived from river sand (~75 %) and paleo-shelf sand (~25 %). The supplies of paleo-shelf sand to the beaches have largely diminished in late-Holocene time. The river-enriched beach sands have been transported offshore to the inner-shelf (0–50 m water depth) to fill increasing accommodation space in the inner-shelf during latest-Holocene conditions of relative SLR (1.0 m ka-1). To evaluate the beach sand response to future SLR, representative beach profiles (n=17) and intervening beach segment distances were compiled to yield beach sand volumes above mean lower low water (MLLW) or shallower wave-cut platforms \u27bedrock\u27. Across-shore cross-sectional areas, as averaged for each subcell, are as follows; Cannon Beach (304 m2), Tillamook (683 m2), and Netarts (227 m2). Littoral sand displacements to the adjacent innermost-shelf (to 30 m water depth) and the marine-dominated areas of the three estuaries are based on assumed vertical sand accretion rates of 1.0 m per century and a conservative value of 0.5 m per century. The filling of such submarine accommodation spaces will displace all active-beach sand reserves in all three subcells for either the 1.0 m or 0.5 m thickness accommodation space scenarios. Large beach sand deficits, primarily from the filling of offshore accommodation spaces, could cause further retreat of soft-shorelines, including barrier spit and beach plain/dune deposits, in the Tillamook subcell (150-280 m) and in the southern half of the Netarts subcell (370-770 m). The accommodation space approach used to predict beach sand volume loss from future SLR should have broad applicability in complex littoral systems worldwide

Widespread Evidence of Terminated Marine Transgressive Sand Supply and Failing Longshore Sand Transport to Eroding Coastal Eolian Sand Ramps during the Latest Holocene Time in Oregon and California (Pacific Coast, USA)

Holocene perched dunes and wave-truncated sand ramps were used to project paleoramp geometries and to estimate sand ramp erosion during the late Holocene in the U.S. Pacific Coast study area (1500 km in length). Both recently accreted sand ramp slopes (n = 24) and wave-truncated sand ramps (n = 59) in 11 sand ramp complexes (0.3–11.4 km in alongshore length) were profiled from areas of previously abundant dune sand supply. Modern sand ramp slopes (shore normal) ranged from 2 to 26°, with slope steepening resulting from upslope eolian deflation (10–20°) and downslope mass wasting by landslide (\u3e 20°). Paleoramp surface slopes at 10, 15, and 20° were projected seaward from truncated sand ramp tops (11–97 m in elevation) to intersect with projected basal ramp horizons (4-m elevation). Differences between the 10° slope paleoramps and the corresponding modern sea cliffs yield eroded ramp cross-sectional areas (78–16,770 m2). The eroded cross-sectional areas were multiplied by corresponding alongshore lengths to estimate truncated ramp complex erosion (1.29 × 105–6.41 × 107 m3, mean 12.62 × 106 m3). Modern beach sand volumes in shorelines fronting the 11 truncated ramp complexes are estimated to range from 1.05 × 105 to 1.47 × 106 m3. The average modern beach sand volume of 4.25 × 105 m3 represents only 3.4% of the average eroded ramp complex volume, as estimated from differencing the 10° projected slopes and the modern sea cliff profiles. Near-surface 14C ages of buried archaeological materials in the 11 truncated ramp complexes (932 ± 672 cal BP 1σ, n = 20) demonstrate terminal ramp accretion and associated ramp truncation by beach retreat during the latest Holocene time. The widespread sand ramp erosion, following 3.0 m of sea-level rise during the last 3.0 ka, serves as a warning for the U.S. Pacific Coast and other high–wave energy cliff-backed shorelines for potential beach response to near-future sea-level rise (1–3 m) predicted to occur from ongoing global warming

The Hooskanaden Landslide: Historic and Recent Surge Behavior of an Active Earthflow on the Oregon Coast

This paper presents an analysis of the Hooskanaden Landslide, an earthflow, which experienced a dramatic surge event beginning on February 24, 2019, closing US Highway 101 near mile point 343.5 for nearly 2 weeks. This ~ 1 km long surge event resulted in horizontal displacements of up to 45 m and uplift of 6 m at the toe located on a gravel beach adjacent to the Pacific Ocean. The Hooskanaden Landslide, likely active since the eighteenth century, exhibits regular activity with a recurrence interval of major surge events of approximately every 20 years, transitioning from slow to relatively rapid velocities. During the 2019 event, maximum displacement rates of approximately 60 cm/h were observed, slowly decreasing to 15 cm/h for a sustained period of approximately 2 weeks before the eventual return to baseline conditions (\u3c 0.02 cm/h)