Mega Tsunami of the World Oceans: Chevron Dune Formation, Micro-Ejecta, and Rapid Climate Change as the Evidence of Recent Oceanic Bolide Impacts

This paper deals with the physical and environmental effects resulting from oceanic impacts by sizable comets, and the rates and risks associated with such cosmic impacts. Specifically, we investigate two sets of probable oceanic impact events that occurred within the last 5,000 years, one in the Indian Ocean about 2800 BC, and the other in the Gulf of Carpentaria (Australia) about AD 536. If validated, they would be the most energetic natural catastrophes occurring during the middle-to-late Holocene with large-scale environmental and historical human effects and consequences. The physical evidence for these two impacts consists of several sets of data: (1) remarkable depositional traces of coastal flooding in dunes (chevron dunes) found in southern Madagascar and along the coast of the Gulf of Carpentaria, (2) the presence of crater candidates (29-km Burckle crater about 1,500 km southeast of Madagascar which dates to within the last 6,000 years and 18-km Kanmare and 12-km Tabban craters with an estimated age of AD 572±86 in the southeast corner of the Gulf of Carpentaria), and (3) the presence of quench textured magnetite spherules and nearly pure carbon spherules, teardrop-shaped tektites with trails of ablation, and vitreous material found by cutting-edge laboratory analytical techniques in the upper-most layer of core samples close to the crater candidates. Although some propose a wind-blown origin for V-shaped chevron dunes that are widely distributed around the coastlines of the Indian Ocean and in the Gulf of Carpentaria, we have evidence in favor of their mega tsunami formation. In southern Madagascar we have documented evidence for tsunami wave run-up reaching 205 m above sea-level and penetrating up to 45 km inland along the strike of the chevron axis. Subtly the orientation of the dunes is not aligned to the prevailing wind direction, but to the path of refracted mega-tsunami originating from Burckle impact crater. The results of our study show that substantive oceanic comet impacts not only have occurred more recently than modeled by astrophysicists, but also that they have profoundly affected Earth’s natural systems, climate, and human societies. If validated, they could potentially lead to a major paradigm shift in environmental science by recognizing the role of oceanic impacts in major climate downturns during the middle-to-late Holocene that have been well documented already by different techniques (tree-ring anomalies, ice-, lake- and peat bog-cores)

Understanding and reducing the disaster risk of landslide-induced tsunamis: a short summary of the panel discussion in the World Tsunami Awareness Day Special Event of the Fifth World Landslide Forum

A World Tsunami Awareness Day Special Event was held in hybrid mode on 5 November 2021, during the Fifth World Landslide Forum, in Kyoto, Japan. In this context, a panel discussion was organized across America, Europe, and Asia, with the goal to better understand and reduce the disaster risk of landslide-induced tsunamis, consistent with the Kyoto Landslide Commitment 2020. This article presents a short summary of this panel discussion

What Are the Origins of V-Shaped (Chevron) Dunes in Madagascar? The Case for Their Deposition by a Holocene Megatsunami

Chevrons are elongated dunes with a V-shaped pattern in map view. In some exposures, smaller Vs are nested within the larger Vs. The term chevron was first used to describe desert dunes (Maxwell and Haynes, 1989) based on their similarity to the nested chevrons used on military uniforms or in heraldry. Chevrons later were identified in coastal regions and proposed to represent megastorm deposits (Hearty et al., 1998; Kindler and Strasser, 2000). Subsequently, other workers suggested that some coastal chevron dunes were tsunami deposits (Bryant and Nott, 2001; Scheffers and Kelletat, 2003; Scheffers et al., 2008). The proposal that some coastal chevron dune complexes represent tsunami deposits is based on three sets of observations (Scheffers and Kelletat, 2003). The first is that the long axes of many coastal chevron complexes are not oriented parallel to the direction of the prevailing wind. The second is that some chevron complexes extend several kilometers (km) inland and rise to over 100 meters (m) above sea level. Some of these chevron complexes are located on shorelines that lack beaches. In these particular cases, it is difficult to understand how either megastorms or wind could have formed the chevrons. Megastorms cannot move subaerial rock and sediment over km-scale distances with elevation gains of hundreds of meters (Cox et al., 2012; Erdmann et al., 2015). Wind cannot move sediment inland if there are no subaerial, poorly consolidated sediments on the coast. In this chapter, we describe three chevron complexes, V-shaped, elongated dune complexes on the southern coast of Madagascar. Their origin is disputed because individual dunes are elongated along an azimuth that is close to the direction of the prevailing winds (Abbott et al., 2008; Pinter and Ishman, 2008), although their low angle of deposition generally is inconsistent with aeolian dunes. However, other characteristics preclude their derivation from modern beach deposits, although we do not discount later aeolian reworking of some chevron deposits. In particular, the Madagascar chevrons contain significant proportions of early Holocene carbonate tests resembling shells of marine foraminifera, including some that are partially dolomitized, and some that are infilled with mud. These observations suggest that marine carbonate tests in the chevrons were eroded from the continental shelf, and not from modern beaches. Furthermore, despite having lateral extents of tens of km, characteristics of the chevrons (degree of sediment sorting, carbonate content, and marine microfossil concentrations) do not change significantly along strike, as might be expected for aeolian deposits

Long Wave Dynamics along a Convex Bottom

Long linear wave transformation in the basin of varying depth is studied for a case of a convex bottom profile in the framework of one-dimensional shallow water equation. The existence of travelling wave solutions in this geometry and the uniqueness of this wave class is established through construction of a 1:1 transformation of the general 1D wave equation to the analogous wave equation with constant coefficients. The general solution of the Cauchy problem consists of two travelling waves propagating in opposite directions. It is found that generally a zone of a weak current is formed between these two waves. Waves are reflected from the coastline so that their profile is inverted with respect to the calm water surface. Long wave runup on a beach with this profile is studied for sine pulse, KdV soliton and N-wave. Shown is that in certain cases the runup height along the convex profile is considerably larger than for beaches with a linear slope. The analysis of wave reflection from the bottom containing a shallow coastal area of constant depth and a section with the convex profile shows that a transmitted wave always has a sign-variable shape.Comment: Submitted to Journal of Fluid Mechanic