Satellite photos taken in April 2023 by Planet Labs PBC and analyzed by the AP showed Iran burrowing into the Kūh-e Kolang Gaz Lā, or “Pickaxe Mountain,” just to the south of the existing perimeter of the known nuclear facility at Natanz (see Image 1), part of the 1500-km Zagros Mountains range extending over Iran, northern Iraq, and southeastern Turkey.

A different set of images analyzed by the James Martin Centre for Nonproliferation Studies revealed that four entrances had been dug into the mountainside, two to the east and another two to the west. Each was 6 metres (20 feet) wide and 8 metres (26 feet) tall.

The scale of the work could be measured in large dirt mounds, two to the west and one to the east. Based on the size of the spoil piles and other satellite data, experts at the James Martin Centre told AP that Iran was likely building a facility at a depth of between 80 metres (260 feet) and 100 metres (328 feet). The Centre’s analysis, which it provided exclusively to AP, was the first to estimate the tunnel system’s depth based on satellite imagery.

The Institute for Science and International Security, a Washington-based nonprofit long focused on Iran’s nuclear program, suggested the tunnels could go even deeper.

The Pickaxe Mountain facility, which since its discovery has been at times referred to as part of one large facility at Natanz, is said to be even deeper underground than the one at Fordow, that was the main target of the US attack on Saturday using its never-used-before GBU-57 bomb, which can plow through at least 60 metres (200 feet) of earth before detonating.

The facility at Pickaxe Mountain, roughly 330 feet below the mountain itself, is between 30 to 70 feet deeper than Fordow. That is believed to exceed the striking depth of the GBU-57, the most powerful bunker-busting weapons in the US arsenal.

The US government’s updates following the attack have not addressed Pickaxe Mountain separately. What we do know from satellite imagery is that the GBU-57s (aka known as the ‘Massive Ordnance Penetrator’ or MOP) created at least 6 craters in Fordow (see Image 2), and two in Natanz. No GBU-57s were dropped in the attack on Esfahan.

Some of the larger craters, upto 6 metres (20 feet) in diameter, would have been targeted more than once to create deeper impact. The craters at Natanz are not as large, suggesting they were each the result of a single impact.

"The larger, central entry holes in the two groupings have irregular shapes and suggest multiple munitions struck the same precise location," N.R. Jenzen-Jones, a munitions specialist and director of the research company Armament Research Services (ARES), told CNN.

"This is consistent with the theory of an attack on such a deeply buried target as the Fordow site, which would require multiple precisely delivered, and carefully calibrated, penetrating munitions to essentially 'smash' and blast their way through to the deeper, more protected areas of the site," he added, CNN reported.

The two craters at Natanz are both located within the perimeter of the original site, away from the newer construction into the side of the mountain (see Image 3). Does that mean Pickaxe Mountain survived the onslaught? Iran has never acknowledged the site’s development or construction and it has retained a lower public profile, with the Institute for Science and International Security first discovering its existence in 2023.

Both Iranian authorities and the International Atomic Energy Agency (IAEA) have indicated that the three key nuclear facilities targeted in the attack did not suffer any radiation leaks. This has led some observers to speculate that Iran may have relocated its critical nuclear assets in advance.

As news of the US strikes was still unfolding, commercial satellite imagery provider Maxar Technologies released a set of images of Fordow taken on June 19 and 20, along with the following statement:

“Prior to tonight’s airstrikes on the three Iranian nuclear-associated facilities, Maxar collected high-resolution satellite imagery on June 19th and June 20th of the Fordow fuel enrichment facility that revealed unusual truck and vehicular activity near the entrance to the underground military complex. On June 19th, a group of 16 cargo trucks were positioned along the access road that leads to the tunnel entrance of the facility. Subsequent imagery on June 20th revealed that most of the trucks had repositioned approximately one kilometer northwest along the access road; however, additional trucks and several bulldozers were seen near the entrance to the main facility and one truck was positioned immediately next to the main tunnel entrance.” 

As of May 17, Iran had amassed 408.6kg (901lb) of uranium enriched up to 60 percent, according to the IAEA. That is still below weapons grade, but the jump from 60% to 93%, good enough for a nuclear bomb, is far easier than the journey from 0-60%. US officials concede they have no idea where this stock of enriched uranium is.

Could the answer lie deep beneath the Zagros Mountains?

It should be mentioned that due to the secretive nature of Iran’s nuclear program, we can never be sure to what extent the facility at Pickaxe Mountain was completed. But Israeli intelligence has shown itself to have penetrated so deep into Iran during this war (and in the past), that it is unlikely they would not know the answer.

And even if the Islamic Republic’s nuclear program does somehow survive, there can be no doubt that it has been dealt a severe, perhaps even crippling, blow over the past 12 days, from which it may never recover.