Large Ancient Impact Crater Likely Found In Southeastern Spain

Spain’s Almeria province has long been known as a shooting location for Italian director Sergio Leone’s gritty ‘60s and ‘70s-era spaghetti westerns. But now a Spanish-led team of international researchers have found what they think is likely a largely buried four-kilometer-wide impact crater located in this same arid area near Spain’s southeastern coast.

Located in Almeria’s Tabernas Basin, the 8-million-year-old crater is surrounded by a larger structure about 22-km across where the impact caused sedimentary strata to collapse, the Europlanet Society reports. Evidence for the crater includes several examples of ‘shocked’ quartz grains in breccia – a sedimentary rock type with large fragments cemented into a finer-grained matrix, the society notes. The grains show signs of being deformed under the impact’s enormous pressures.

The team writes that the crater was likely originally formed in a shallow marine paleoenvironment. Yet researchers caution they’re not offering absolute proof of such an impact. That will only come with core drilling into the impact crater itself.

While around 200 impact structures have been identified around the world, this study is the first to identify signs of an impact crater on the Iberian Peninsula, the Europlanet Society notes.

Can anything yet be determined about the original size of the impactor?

There’s a perfect relation between the size of the impactor and the size of the crater, Jens Ormo, a geologist specializing in marine shallow water impactors at the Centro de Astrobiología (CAB), told me in his office outside Madrid. The crater is usually 10 to 15 times larger than the impactor, he says. So, divide this crater’s four-kilometer width by 10 and you get a 400-meter-wide impactor, he notes.

When an asteroid strikes, you get this high energy that basically liquifies the rock momentarily, says Ormo. It’s not necessarily all melting, it’s just losing its strength, he says. So, the crater develops in a liquid form for a while until the rock becomes stable and strong again, says Ormo.

As for how this years-long process of impactor detective work got started?

My colleagues at the University of Almeria started to realize that something is strange with the geology there, says Ormo. Without an impact scenario, he says it’s hard to explain how you such older crystalline rocks could end up lying on top of much younger sedimentary rocks. But this impact pierced a 4-kilometer-wide hole which caused material to be strewn out in a massive ejecta layer over all these younger sedimentary rocks, he says.

As for the impact’s immediate effects?

If it happened today Madrid would be leveled, says Ormo. Temperatures over the impact site would have been tens of thousands of degrees, he says. That would be followed by an atmospheric shock wave that would create hurricane force winds up to 100-km away from the strike zone.

You toast everything first, and then you just blow it away, says Ormo. Then you have tremendously strong earthquakes of maybe a magnitude 10 on the Richter Scale, he says.

Ormo operates out of a tiny office at the end of a long corridor. But his scientific pride and joy is a facility which he has mostly constructed from scratch in a large adjoining industrial-sized test chamber next door.

I literally follow him up a crude metal ladder to the top of a large metal funnel and onto the structure’s bullseye where he and colleagues shoot projectiles to simulate Earth impactors in shallow marine environments. The Experimental Projectile Impact Chamber (EPIC) is a specially designed facility for the study of processes related to wet-target impacts, the CAB notes. It consists of a 7-meter wide, funnel-shaped test bed, and a 20.5-mm caliber compressed nitrogen gas gun, says the CAB.

We shoot projectiles that disintegrate upon impact, because that’s a better analog to the natural effects of hypervelocity impacts, says Ormo.

We have enough evidence now to make a strong case for an impact crater, says Ormo. It’s just not proven yet, he says.

To prove beyond a reasonable doubt that the putative crater is really from an impact, the team needs to do costly deep drilling down to a depth of a kilometer. Ormo hopes to get a $150,000 drilling grant to get it done soon.

Now, his team only has a handful of shocked quartz grains, indicative of an impactor creating very high pressures and telltale striations in the quartz. But the team would need several dozen quartz grains from deep beneath the putative crater in order to make a statistical analysis that would conclusively point to an impact.

Ormo says one reason the study of such impactors is important because they had such influence in shaping Earth’s climate, geography, and the onset and destruction of life as we know it. He thinks our planet may harbor as many as 500 more such impact craters of at least a kilometer in size that have yet to be detected.

As for the probable one at Almeria?

It’s almost humorous to think of the laconic Clint Eastwood on location in Almeria; chewing on a butt of a stogie, staring down some onery-looking hombre in films like “A Fistful Of Dollars.”

Little did Eastwood or anyone know at the time that he was walking across part of Earth’s heretofore unknown ancient history, completely unaware that he was likely in the middle of an impact ejecta blanket. One where a still unknown impactor likely encroached on our planet to wreak more havoc than anything a spaghetti western could muster.