Highlights

Satellite imagery taken over the last months show that Iran is continuing construction activities at the Natanz “Pickaxe” mountain, or Mt Kolang Gaz-La, in line with activity at the site prior to the June war.  As of September 2025, Iran’s visible activities point towards late stages of construction, including improving security, but represent neither an expansion of the site nor an acceleration of activity.  They do not indicate an ability to quickly rebuild destroyed parts of its nuclear program.  Rather, Iran appears to have two main choices for the site: Cobble together remaining assets into this closely watched facility, exposing high value targets for follow-on strikes, such as highly enriched uranium stocks, during recovery from rubble and transport, or slowly build and accumulate new capabilities, where anything imported from abroad or produced by Iranian companies outside the military industry would have to be closely scrutinized for quality and potential sabotage.

The Institute has monitored the Pickaxe mountain site since the beginning of its construction in late 2020, describing the depth and potential size of the tunnel facility, hardened entrances, and additional security measures, including the construction of a wall and fence surrounding the entire mountain base.  This analysis raises questions about the nuclear activities Iran has planned for the site, specifically whether it includes plans for an enrichment plant. 

As of June 2025, the facility was not assessed as operational, and the current construction activities support that view. This could be a key reason why the site was not attacked by airstrikes in the June war, although a different kind of attack on the site cannot be excluded, and there have been rumors of such an attack. 

However, the mountain area south of Natanz includes another tunnel facility, built years earlier and associated with the Natanz enrichment site.  This facility also shows ongoing activity, specifically hardening the tunnel entrances.  An important question for this tunnel facility is whether Iran was able to move high value assets into it. 

Figure 1.  An overview satellite image from September 22, 2025, of the mountainous area south of Natanz FEP, which contains two tunnel facilities that show recent activity. 

Visible Activity at Mount Kolang-Gaz La

Satellite imagery taken in September show progress made with respect to the security perimeter, including the completion of the primary wall perimeter, which was still missing portions on the west side in late March 2025.^[1]  The security perimeter Iran established surrounds the entire mountain range, including the foot of Mt Kolang Gaz La and a nearby mountain housing a tunnel complex built in 2007.  Imagery dated to September 22, 2025, show that as expected, the security perimeter is not only composed of wall panels, but now shows signs of becoming a double-perimeter:  A fence is being built behind the wall, so that any intruder needs to scale the wall and cross an area that will likely become an electronic surveillance zone before facing the fence.  Guard towers and a security patrol road can be expected in the future.  In the meantime, absent lights, video cameras, motion sensors, watch towers, alarm systems etc. these current features are physical obstacles but likely ineffective against prepared intruders. See Figures 1 and 2. 

Imagery dated to late June and early August further show activity at the second eastern tunnel portal, which is labeled as the main tunnel portal in earlier Institute reports. Vehicles can be seen on the road leading in and out of the tunnel portal.  This tunnel entrance is the only of the four that has not seen significant stabilization work, possibly due to unexpected issues in the encountered geology as evidenced by the consistent visible waterflow stemming from the entrance. It appears that Iran has finally turned its attention to finishing this last tunnel portal as the tunnel complex is otherwise nearing completion (see Figure 3).

In parallel, a shift in the spoil pile near the eastern tunnel entrances is noted, likely due to finishing the main eastern tunnel portal and covering the tunnel extension frame of the auxiliary eastern tunnel portal with rock.  As of September 22, various construction materials are visible in the small construction support area of the eastern tunnel entrances as well as along the road and on top a small area of the spoil pile. These are further indications that activities inside the tunnel are focused on completing ongoing construction rather than conducting major additional excavation (see Figure 4).   

Figure 2.  A close-up of the multi-level security perimeter under construction at Pickaxe Mountain. 

Figure 3.  The set of eastern tunnel entrances on June 30, 2025 (top) and August 2, 2025 (bottom).   

Figure 4.  Construction materials near the eastern tunnel entrances. 

Hardening of the 2007 Tunnel Complex

An August 10, 2025, MAXAR Technologies satellite image shows that the tunnel entrances leading into the original tunnel complex dating from 2007, as well as alcoves that were built more recently, are being reinforced with slabs of thick concrete and then buried in soil (see Figure 5).  This is an apparent effort to harden the entrances and alcoves from any potential airstrike or sabotage operation. 

The Institute has previously reported on this site, which was dormant for more than a decade and then was slowly reactivated about five years ago, with dramatic changes in the inner security perimeters at its tunnel entrances during the last two years. The two tunnel entrances are highly secured with entrance security buildings and moveable roadblocks leading to the upper one.  The security perimeter of the upper tunnel entrance was changed and an elaborate extension with alcoves was added, where alcoves could have a multitude of uses, including housing utilities for the main tunnel. 

Using concrete slabs as reinforcement was previously observed at the Fordow Fuel Enrichment Plant, where prior to the June 22 attack by the United States during Operation Midnight Hammer, the air ventilation shafts were reinforced with concrete pads. Iran’s post-June rush to add these pads to the Natanz tunnel site raises important questions about whether Iran was able to move any nuclear material, specifically enriched uranium stocks, or nuclear-related equipment, into the facility before the U.S. struck the other sites on June 22.  This concern is heightened by satellite imagery dated June 18, 2025, which shows a truck leaving the tunnel facility area at around 9 AM local time. 

Figure 5.  Concrete slabs being installed to reinforce the 2007 tunnel entrances and the recently added alcoves. 

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Sources

^[1]David Albright, Sarah Burkhard, and the Good ISIS Team, “New Security Perimeter Around Mt. Kolang Gaz La Secret Nuclear Tunnel Complexes,” Institute for Science and International Security, April 23, 2025, https://isis-online.org/isis-reports/new-security-perimeter-around-mt-kolang-gaz-la-secret-nuclear-tunnel-complexes; See also: https://www.washingtonpost.com/national-security/2025/09/26/iran-underground-nuclear-us. Note: The headline and lede are hyped up in their description of activity increasing after the strikes, which is not supported by the article itself and the Institute’s analysis for the article.