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Recent ice-mass loss driven by warming along the Antarctic Peninsula has resulted in rapid changes in uplift rates across the region. Are such events only a function of recent warming? If not, does the Earth response to such events last long enough to be preserved in Holocene records of relative sea level (RSL), and thus have a bearing on global-scale glacial isostatic adjustment (GIA) models (e.g. ICE-6G)? Answering such questions in Antarctica is hindered by the scarcity of RSL reconstructions within the region. Here, a new RSL reconstruction for Antarctica is presented based on beach ridges from Joinville Island on the Antarctic Peninsula. We find that RSL has fallen 4.9 ± 0.58 m over the past 3100 yr, and that the island experienced a significant increase in the rate of RSL fall from 1540 ± 125 cal. (calibrated) yr B.P. to 1320 ± 125 cal. yr B.P. This increase in the rate of RSL fall is likely due to the viscoelastic response of the solid Earth to terrestrial ice-mass loss from the Antarctic Peninsula, similar to the Earth response experienced after ice-mass loss following acceleration of glaciers behind the collapsed Larsen B ice shelf in 2002 C.E. Additionally, slower rates of beach-ridge progradation from 695 ± 190 cal. yr B.P. to 235 ± 175 cal. yr B.P. potentially reflect erosion of beach ridges from a RSL rise induced by a local glacial advance. The rapid response of the Earth to minor ice-mass changes recorded in the RSL record further supports recent assertions of a more responsive Earth to glacial unloading and at time scales relevant for GIA of Holocene and Pleistocene sea levels. Thus, current continental and global GIA models may not accurately capture the ice-mass changes of the Antarctic ice sheets at decadal and centennial time scales.

Tsunamis generated by great earthquakes threaten coastal infrastructure, development, and human life. Earlier work has documented the inland extent and frequency of past tsunamis, but litle is known about the magnitude of material eroded during prehistoric tsunamis and how erosion and coastal recovery are recorded in coastal stratigraphy. In this study we use high-resolution ground-penetrating radar (GPR) to image and quantify coastal erosion experienced during a late Holocene (~900 cal BP) Cascadia subduction zone earthquake and tsunami along the northern California coast. The GPR profiles illustrate three stratigraphic signatures created during co-seismic subsidence and tsunami erosion and coastal recovery. The first is erosional truncation of the underlying seaward-dipping reflections created

Observations from ground‐penetrating radar, sediment cores, elevation surveys and aerial imagery are used to understand the development of the Elwha River delta in north‐western Washington, USA, which prograded as a result of two dam removals in late 2011. Swash‐bar, foreshore and swale depositional elements are recognized within ground‐penetrating radar profiles and sediment cores. A model for the growth and development of small mountainous river wave‐dominated deltas is proposed based on observation of both the fluvial and deltaic settings. If enough sediment is available in the fluvial system, mouth‐bars form after higher than average river discharge events, creating a large platform seaward of the subaqueous delta plain. Swash‐bars form concurrently or within a month of mouth‐bar deposition as a result of wave action. Fair‐weather waves drive swash‐bar migration landward and in the direction of littoral drift. The signature of swash‐bar welding to the shoreline is landward‐dipping reflections, as a result of overwash processes and slipface migration. However, most swash‐bars are eroded by the river mouth, as only 10 of the 37 swash‐bars that formed between August 2011 and July 2016 survived within the Elwha River delta. The swash‐bars that do survive either amalgamate onto the shoreline or an earlier deposited swash‐bar, forming a single larger barrier at the delta front. In asymmetrical deltas, the signature of swash‐bar welding is more likely to be preserved on the downdrift side of the delta, where formation is more likely and accommodation behind newer swash‐bars preserves older deposits. On small mountainous river deltas, welded swash‐bars may be more indicative of a large sediment pulse to the system, rather than large hydrological events.

High-resolution 2-D multichannel seismic data, collected during the 2012 UTIG-USGS National Earthquake Hazards Reduction Program survey of Disenchantment and Yakutat Bays in southeast Alaska, provide insight into their glacial history. These data show evidence of two unconformities, appearing in the form of channels, and are interpreted to be advance pathways for Hubbard Glacier. The youngest observable channel, thought to have culminated near the main phase of the Little Ice Age (LIA), is imaged in Disenchantment Bay and ends at a terminal moraine near Blizhni Point. An older channel, thought to be from an advance that culminated in the early phase of the LIA, extends from Disenchantment Bay into the northeastern edge of Yakutat Bay, turning southward at Knight Island and terminating on the southeastern edge of Yakutat Bay. Our interpretation is that Hubbard Glacier has repeatedly advanced around the east side of Yakutat Bay in Knight Island Channel, possibly due to the presence of Malaspina Glacier cutting off access to central Yakutat Bay during times of mutual advance. We observe two distinct erosional surfaces and retreat sequences of Hubbard Glacier in Yakutat Bay, supporting the hypothesis that minor glacial advances in fjords do not erode all prior sediment accumulations. Interpretation of chaotic seismic facies between these two unconformities suggests that Hubbard Glacier exhibits rapid retreats and that Disenchantment Bay is subject to numerous episodes of outburst flooding and morainal bank collapse. These findings also suggest that tidewater glaciers preferentially reoccupy the same channels in bay and marine settings during advances.

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