Large ancient impact crater likely found in southeastern Spain

Spain’s Almeria province has long been known as the filming location for Italian director Sergio Leone’s gritty spaghetti westerns of the 1960s and 1970s. But now a Spanish-led team of international researchers has discovered what they believe is likely a four-kilometer-wide buried impact crater located in the same arid region near Spain’s southeastern coast.

Located in Almería’s Tabernas Basin, the 8-million-year-old crater is surrounded by a larger structure about 22 kilometers across where the impact caused sedimentary layers to collapse, the Europlanet Society reports. Evidence for the crater includes several examples of “shocking” quartz grains in breccias – a type of sedimentary rock with large fragments cemented in a fine-grained matrix, the society notes. The grains show signs of deformation under the enormous pressures of the impact.

The team writes that the crater likely originally formed in a shallow marine paleoenvironment. However, the researchers caution that they do not offer absolute proof of such an effect. This will only be done by coring the impact crater itself.

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

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

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

When an asteroid hits, you get this high energy that essentially liquefies the rock instantly, Ormo says. It doesn’t necessarily melt, it just loses its strength, he says. So the crater grows in liquid form for a while until the rock becomes solid and strong again, Ormo says.

As for how this years-long sleuthing process began?

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

As for the immediate effects of the impact?

If it happened today Madrid would be flattened, says Ormo. Temperatures above the impact point would be tens of thousands of degrees, he says. This would be followed by an atmospheric shock wave that would generate hurricane-force winds up to 100 kilometers away from the impact zone.

First you toast everything and then you blow it, says Ormo. Then you have tremendously strong earthquakes of maybe magnitude 10 on the Richter scale, he says.

Ormo operates from a tiny office at the end of a long hallway. But his scientific pride and joy is a facility he has mostly built from scratch in a large adjacent industrial test chamber next door.

I literally follow him up a crude metal ladder atop a large metal funnel and into the bullseye of the structure, where he and his colleagues launch projectiles to simulate Earth impactors in shallow marine environments. The Experimental Projectile Impact Chamber (EPIC) is a purpose-built facility to study processes associated with liquid target impacts, the CAB notes. It consists of a 7-meter-wide, funnel-shaped test bed and a 20.5 mm compressed nitrogen gas gun, the CAB says.

“We shoot projectiles that disintegrate on impact because that’s a better analogy for the physical effects of hypervelocity impacts,” Ormo says.

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

To prove beyond a reasonable doubt that the supposed crater is really from an impact, the team must do expensive deep drilling to a depth of one kilometer. Ormo hopes to receive a $150,000 drilling grant to do so soon.

Now, his team has only a handful of shocked quartz grains, indicative of a shock pendulum that creates very high pressures and telltale striations in the quartz. But the team would need several dozen grains of quartz from deep below the supposed crater in order to do a statistical analysis that would definitively indicate an impact.

Ormo says one reason studying such impactors is important is because they had such an influence on shaping Earth’s climate, geography, and the initiation and destruction of life as we know it. He believes our planet may host up to 500 more such impact craters at least one kilometer in size that have yet to be identified.

As for the possible in Almeria?

It’s almost humorous to think of the laconic Clint Eastwood on location in Almería. chewing the butt of an arcade, glaring at some lonely host in movies like ‘A Fistful Of Dollars’.

Little did Eastwood or anyone know at the time that he was walking into part of Earth’s heretofore unknown ancient history, completely unaware that he was likely in the middle of an impact launch blanket. Where yet another unknown thug has probably invaded our planet to wreak more havoc than anything a spaghetti western could muster.

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