Massive Eltanin Meteor 2.5 million years ago set off mass tsunami, changed the climate?

From the file of “Things that would really be catastrophic”. Did a meteor have a role in a major shift in Earth’s Climate?

The start of the Quaternary period (2.588 million years ago, where the Pliocene became Pleistocene) coincides with evidence of a mega tsunami in the South Pacific.

The Eltanin Meteor fell into the South Pacific 2.5 million years ago setting off a (likely) tsunami that was hundreds of meters high and theoretically pushed mass material into the atmosphere which may have contributed to the cooling the globe had already started on. This meteor was hard to detect because it hit the ocean rather than the land. But researchers have pieced together evidence of the mass tsunami on continents around the pacific rim.

Bob Beale of UNSW via Science Daily.

“This is the only known deep-ocean impact event on the planet and it’s largely been forgotten because there’s no obvious giant crater to investigate, as there would have been if it had hit a landmass,” says Professor James Goff, lead author of a forthcoming paper in the Journal of Quaternary Science. Goff is co-director of UNSW’s Australia-Pacific Tsunami Research Centre and Natural Hazards Research Laboratory.

“But consider that we’re talking about something the size of a small mountain crashing at very high speed into very deep ocean, between Chile and Antarctica. Unlike a land impact, where the energy of the collision is largely absorbed locally, this would have generated an incredible splash with waves literally hundreds of metres high near the impact site.

As a ‘cene’ changer — that is, from the Pliocene to Pleistocene — Eltanin may have been overall as significant as the meteor that took out the non-flying dinosaurs 65 million years ago. We’re urging our colleagues to carefully reconsider conventional interpretations of the sediments we’re flagging and consider whether these could be instead the result of a mega-tsunami triggered by a meteor.”

From the paper (paywalled)

The Eltanin asteroid is currently the only known impact into a deep ocean (4–5 km) basin, striking the Southern Ocean about 1500 km SSW of Chile (Fig. 1). Although there is no crater on the seafloor, meteoritic material was found in sedimentary rocks
collected at three places 500 km apart. There were also traces of intense erosion as well as the deposition of eroded material
(Gersonde et al., 1997). Gersonde et al. (1997) estimated the asteroid to be between 1 and 4 km in diameter.

Other more recent estimates suggest it must have been less than 2km “a larger size would cause impact melt on the seafloor and create a bottom crater…”

Estimates of the height of the wave vary from 20 – 300m as it hit the coast of South America. The smaller estimate is more recent. In any case the run up estimates on land are up to 10 – 25 times higher. There are beds of bones in Peru where fragments of land and marine creatures from a calm environment are deposited together  and in ways that suggest it was rapid.

In New Zealand, deposits have been raised high above sea level thanks to techtonic movements. At the time of the impact New Zealand was closer to sea level, and some areas would have been completely washed over.

I understand why a land impact would send material into the atmosphere and block out sunlight, cooling the planet, but I’m less sure of why a deep sea impact and tsunami would do that. Evidently this is a “modeled” result, so I’ll keep my skeptical hat on about whether a deep sea impact could cool the planet significantly. The timing with the Pleistocene boundary might be coincidental.

“Some modelling suggests that the ensuing mega-tsunami could have been unimaginably large – sweeping across vast areas of the Pacific and engulfing coastlines far inland. But it also would have ejected massive amounts of water vapour, sulphur and dust up into the stratosphere.

From the paper (paywalled)

In the case of the Eltanin impact it is estimated that the impact would have  led to a 5- to 50-fold increase in the mass of S in the stratosphere (21011 g). With sufficient O and H in the vapour plumes of most impact events to convert the S to sulfuric acid aerosols, the effects of a moderately large deep ocean impact such as Eltanin may fall somewhere between that of a Mount Pinatubo eruption (multi-year depression of global temperatures by at least 0.5 8C) and Chicxulub (a 2 8C depression for 3 years or longer). Furthermore, any excess H2O not used to produce sulfuric acid aerosols may condense as water ice, increasing
planetary albedo and interacting with any veil of atmospheric dust that might be present. Although the longer residence
time of water vapour in the stratosphere as opposed to the troposphere could actually lead to either a warming
(greenhouse effect) or a cooling (ice clouds) (Gisler et al., 2011), the potential effects of which are beyond the scope of this paper, this could conceivably be seen as one of the climatic drivers marking the start of the Quaternary 2.58Ma ago.

Abstract

Large asteroid impacts are rare, and those into the deep ocean are rarer still. The Eltanin asteroid impact around 2.51 ± 0.07 Ma occurred at a time of great climatic and geological change associated with the Pliocene–Pleistocene boundary. Numerical models of the event indicate that a megatsunami was generated, although there is debate concerning its magnitude and the region-wide extent of its influence. We summarise the existing evidence for possible Eltanin megatsunami deposits in Antarctica, Chile and New Zealand, while also examining other potential sites from several locations, mainly around the South Pacific region. In reviewing these data we note that these events were unfolding at the same time as those associated with the Pliocene–Pleistocene boundary and, as such, most of the geological evidence from that time has a climatic interpretation. The potential climatic and geological ramifications of the Eltanin asteroid impact, however, have failed to be considered by most researchers studying this time period. Although we are not advocating that all geological activity at that time is connected with the Eltanin asteroid impact, it raises interesting questions about the role potentially played by such catastrophic events in contributing to or even triggering epochal transitions. Copyright © 2012 John Wiley & Sons, Ltd.

 What’s the next big one coming?

It’s virtually 100% certain (not just “very likely”) that the next big one is on the way, sometime, and when it hits, it will be catastrophic, millions will die, species will be wiped out, and the climate will change. So where is the UN Meteor Watch Program? Where are the activists telling us to buy insurance?  Could it be that no one cares because there is no Meteor Market, no Departments of Astro-catastrophe, no Meteor Shield Industry and no $10 billion dollar programs to research the mitigation options, the after effects, or the psychology of meteor-deniers?

Ah, you say, it’s because the odds are small and there’s nothing we can do anyhow. But then nuking a big rock far out in space is far more believable than changing light-bulbs to hold back the tide, or building a bike path to change the weather, both of which are now national policy.

REFERENCE

James Goff, Catherine Chagué-Goff, Michael Archer, Dale Dominey-Howes, Chris Turney. The Eltanin asteroid impact: possible South Pacific palaeomegatsunami footprint and potential implications for the Pliocene-Pleistocene transition. Journal of Quaternary Science, 2012; DOI: 10.1002/jqs.2571

Hat tip to Mark at UWA.