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At Tanis, a unique bi‐directional sediment package occurs precisely at the Cretaceous‐Paleogene (K‐Pg) boundary, recording the first hours of the Paleogene in uncommonly fine temporal detail. The impact ejecta‐bearing sediment package was rapidly emplaced by two massive, ∼10‐m‐high, potentially impact‐triggered surges, that inundated a steep, deeply incised paleo river valley from the direction of the contemporaneous Western Interior Seaway (WIS). Intermingling of fresh‐ and salt‐water fossils at Tanis, coeval brackish water indicators in the nearby region, and historical tsunami observations, suggest that the WIS paleoshoreline was nearby Tanis at K‐Pg time. The interpreted timing for deposition (including ejecta infall) of ∼1–2‐hr immediately post‐impact precludes a direct tsunami from the Chicxulub impact site, which would have required much more than 10 hr to reach Tanis. Seismic waves from the Mw ∼ 11 Chicxulub earthquake, arriving just minutes post‐impact, might have triggered the surge, for example, via seismic excitation of large water waves in the WIS, as proposed by DePalma et al. (2019, https://doi.org/10.1073/pnas.1817407116). Here, we explore this mechanism via a simple mathematical model of seismic excitation and propagation of a water wave into a shallow river and upstream. Matching the observations implies a relatively long source process time of many minutes, such as generated by Chicxulub crater rebound processes, in order to explain sufficient upriver amplitudes and advective transport. Atmospheric waves due to the expanding Chicxulub ejecta curtain might have provided a smaller, secondary contribution during triggering. Thus, the mechanism(s) for the surges at Tanis are now better‐constrained, yet remain incompletely resolved. Plain Language Summary: A remarkable geological record at the "Tanis" site (North Dakota) shows that two ∼10 m high tsunami‐like surges occurred on a point bar along a river upstream from the then existing Western Interior Seaway (WIS). The surge deposits are interpreted to have occurred within 1–2 hr of the Chicxulub impact associated with the end‐Cretaceous mass extinction including the dinosaurs, and are challenging to explain via traditional tsunami mechanisms because they occurred too soon after the impact to have been tsunami waves traveling from the impact site. Alternative explanations include excitation of large water waves in the WIS due to seismic shaking from the magnitude ∼11 impact‐generated earthquake or atmospheric effects from the expanding impact ejecta curtain. Here, we explore one potential triggering mechanism via a simple mathematical model of direct seismic excitation and propagation of a water wave into a shallow river and upstream. This model shows the difficulty of generating the observed surge deposits unless the timescale for impact‐generated seismic waves is much longer than is commonly presumed. Thus the actual triggering mechanism(s) of the Tanis depositional surges remains incompletely resolved, while the sediment package bears a rich source of information about the global effects of the Chicxulub impact. Key Points: An ∼10 m surge event coincident with the Chicxulub impact transported mixed freshwater/marine organisms up the Tanis river valleyNew modeling confirms limitations on the inland transport of marine fossils and helps to constrain the impact‐related triggering mechanismOther potential triggering mechanisms and strategic avenues of future study are discussed [ABSTRACT FROM AUTHOR]

Abstract Although many studies have attempted to reconstruct millennial‐scale hurricane patterns using various proxy‐based methods, it is still unclear what the most effective proxies are to identify storm surge deposits in different environmental settings. This study quantitatively compares the application of grain‐size, loss‐on‐ignition, stable isotopes, X‐ray fluorescence, and palynological proxies in paleotempestology from an organic‐rich environment in the Florida Everglades. The nonparametric tests indicate that only 9 among the 27 parameters (mean diameter, %water, %organic, %carbonate, Ca, Sr, Ca/Ti, Cl/Br, and marine microfossils) exhibited significant differences between storm‐surge and in situ deposits. The principal component analysis shows that five marine indicators (Sr, Ca, Ca/Ti, %Carbonate, and Marine microfossils) have the closest association with the allochthonous samples, while Cl/Br and Mz are the most sensitive proxies in low‐ and high‐energy environments, respectively. Moreover, organic geochemical proxies (e.g., δ13C and δ15N of bulk sedimentary organic matter) are ineffective for identifying storm‐surge deposits in organic‐rich mangrove environments.

Hazard assessments in monogenetic volcanic fields require estimates of the runout of pyroclastic surges that result from phreatomagmatic explosive activity. Previous assessments used runout distances of 1–4 km, with large cases up to 6 km. Surge deposits at Ubehebe Crater (∼2100 y.b.p., Death Valley, California) have been traced ∼9 km from the crater center, and likely originally extended 1–3 km farther. There is no evidence that the Ubehebe Crater activity was unusually energetic; rather, its distal deposits are better preserved than those at most maar volcanoes because of its young age and the arid environment. Numerical simulations illustrate how low temperatures facilitate long runout of phreatomagmatic surges due to reduced expansion of entrained air compared to hot surges, allowing cool surges to retain higher densities than ambient air. We suggest that hazard assessments for volcanic fields with phreatomagmatic, maar‐forming eruptions should consider runout distances in the range of 10–15 km. Plain Language Summary: Assessments of volcanic hazards in areas prone to small‐volume basaltic volcanoes includes consideration of the lateral extent of devastating pyroclastic surges from eruptions that are caused by magma‐water explosions. Previous assessments considered surge distances up to 6 km, but the deposits from Ubehebe Crater (Death Valley, California, USA) have been traced to 9 km and likely originally extended farther. This was not an unusual eruption, but its deposits are exceptionally preserved due to the arid environment. Pyroclastic surges from magma‐water explosions are likely to be cooler than other volcanic flows, and this facilitates long travel distances and hence far‐reaching potential impacts if the area is inhabited. We suggest that future assessments should consider pyroclastic surge distances of 10–15 km from the vent. Key Points: Hazard assessments in monogenetic volcanic fields have considered pyroclastic surge runout up to 6 km based upon preserved deposits of previous eruptionsSurge deposits from Ubehebe Crater extend to 9 km; this may not be unusual and such surges may have long runout facilitated by their low temperaturesWe suggest that future hazard assessments in monogenetic volcanic fields consider pyroclastic surge runout up to 10–15 km [ABSTRACT FROM AUTHOR]

Although many studies have attempted to reconstruct millennial‐scale hurricane patterns using various proxy‐based methods, it is still unclear what the most effective proxies are to identify storm surge deposits in different environmental settings. This study quantitatively compares the application of grain‐size, loss‐on‐ignition, stable isotopes, X‐ray fluorescence, and palynological proxies in paleotempestology from an organic‐rich environment in the Florida Everglades. The nonparametric tests indicate that only 9 among the 27 parameters (mean diameter, %water, %organic, %carbonate, Ca, Sr, Ca/Ti, Cl/Br, and marine microfossils) exhibited significant differences between storm‐surge and in situ deposits. The principal component analysis shows that five marine indicators (Sr, Ca, Ca/Ti, %Carbonate, and Marine microfossils) have the closest association with the allochthonous samples, while Cl/Br and Mz are the most sensitive proxies in low‐ and high‐energy environments, respectively. Moreover, organic geochemical proxies (e.g., δ13C and δ15N of bulk sedimentary organic matter) are ineffective for identifying storm‐surge deposits in organic‐rich mangrove environments. Plain Language Summary: To help objectively identify the occurrence of storm‐surge deposits in coastal sediment cores, this study uses a statistical approach to evaluate the effectiveness of 27 widely used sedimentological, organic and inorganic geochemical, and biological parameters in distinguishing allochthonous deposits from autochthonous deposits in an organic‐rich environment in the Florida Everglades. The results show that Ca, Sr, Ca/Ti, and marine microfossil are four of the most sensitive parameters to distinguish storm‐surge deposits in organic‐rich environments in south Florida. In addition, Cl/Br can be used to indicate storm surge inundation in further inland and lower‐energy environments. Moreover, organic geochemical proxies cannot effectively distinguish storm‐surge deposits from in situ deposits in mangrove‐dominated coastal zones. Future studies need to explore the use of more specific organic geochemical proxies (e.g., biomarker) in mangrove‐dominated environments and evaluate the effective proxies in detecting storm deposits from sandy, deltaic/estuarine, and nontropical coastal environments. Key Points: Ca, Sr, Ca/Ti, and marine microfossil are the most sensitive parameters to identify storm‐surge deposits in organic‐rich environmentsCl/Br can be used to indicate storm surge inundation in further inland and lower energy environmentsOrganic geochemical proxies cannot effectively distinguish storm‐surge deposits from in situ deposits in mangrove‐dominated coastal zones [ABSTRACT FROM AUTHOR]

Sand-wave structures of both progressive (downstream migrating) and regressive (upstream migrating) types occur within the same pyroclastic-surge deposit at both Roccamonfina volcano (southern Italy) and Sugarloaf Mountain (Arizona, United States). Both 'wet' and 'dry' surge deposits are described that contain examples of regressive and progressive sandwave structures. At Sugarloaf Mountain progressive and regressive sand waves occur within metres of each other within the same bedset, indicating that penecontemporaneous deposition of the two different sand-wave structures occured in close proximity. On the basis of this evidence it is suggested that the migration direction of sand waves in these pyroclastic-surge deposits is controlled by the flow regime of the surge rather than the temperature and/or moisture content.

Abstract: Cora Maar is a Quaternary volcano located to the 20 km northwest of Mount Erciyes, the largest of the 19 polygenetic volcanic complexes of the Cappadocian Volcanic Province in central Anatolia. Cora Maar is a typical example of a maar-diatreme volcano with a nearly circular crater with a mean diameter of c.1.2 km, and a well-bedded base surge-dominated maar rim tephra sequence up to 40 m in thickness. Having a diameter/depth ratio (D/d) of 12, Cora is a relatively “mature” maar compared to recent maar craters in the world. Cora crater is excavated within the andesitic lava flows of Quaternary age. The tephra sequence is not indurated, and consists of juvenile clasts up to 70 cm, non-juvenile clasts up to 130 cm, accretionary lapilli up to 1.2 cm in diameter, and ash to lapilli-sized tephra. Base surge layers display well-developed antidune structures indicating the direction of the transport. Both progressive and regressive dune structures are present within the tephra sequence. Wavelength values increase with increasing wave height, and with large wavelength and height values. Cora tephra display similarities to Taal and Laacher See base surge deposits. Impact sags and small channel structures are also common. Lateral and vertical facies changes are observed for the dune bedded and planar bedsets. According to granulometric analyses, Cora Maar tephra samples display a bimodal distribution with a wide range of Md φ values, characteristic for the surge deposits. Very poorly sorted, bimodal ash deposits generally vary from coarse tail to fine tail grading depending on the grain size distribution while very poorly sorted lapilli and block-rich deposits display a positive skewness due to fine tail grading. [Copyright &y& Elsevier]