A deliberate explosion inside the Kakhovka dam, on the front lines of the war in Ukraine, most likely caused its collapse on Tuesday, according to engineering and munitions experts, who said a structural failure or an attack from outside the dam were possible but less plausible explanations.
Ukrainian authorities blamed Russia for the collapse, noting that Moscow's military forces — which have repeatedly attacked Ukrainian infrastructure since their invasion last year — controlled the dam that spans the Dnipro River, allowing them to detonate explosives from inside.
The streets of Kherson were submerged on Tuesday after the blowing up of the Kakhovka dam. Photo Evgeniy Maloletka/Associated Press
Russian authorities, for their part, blamed Ukraine but did not explain how.
For months, each side of the war has repeatedly accused the other of plotting to sabotage the hydroelectric dam, without providing evidence, accusations that rarely rose above the warlike fog of claims and counterclaims, both real and fabricated.
Last week, both said an attack on the dam was imminent; Ukrainian officials said the Russians wanted to create an emergency situation at the Zaporizhzhia nuclear power plant, which uses river water for cooling, in order to paralyze an expected Ukrainian offensive.
"It was mined by the Russian occupiers. And they blew it up," Ukrainian President Volodymyr Zelensky wrote on social media.
Ihor Syrota, director of Ukrhydroenergo, the state-owned hydroelectric company, said in an interview:
"A missile attack would not cause such destruction because this plant was built to withstand an atomic bomb."
He added: "It is clear: there was an explosion from inside the plant and it broke in half."
But Kremlin spokesman Dmitry S. Peskov told reporters:
"We are talking about deliberate sabotage on the Ukrainian side."
John Kirby, a spokesman for the White House National Security Council, said he could not comment on who was responsible.
"We are working with the Ukrainians to gather more information," he said.
Experts cautioned that the available evidence was very limited, but claimed that an internal explosion was the most likely explanation for the destruction of the dam, a huge steel-reinforced concrete structure that was completed in 1956.
And local residents reported on social media that they had heard a large explosion around the time the dam broke, at 2:50 a.m.
Structure
An explosion in an enclosed space, with all its energy applied against the surrounding structure, would cause the most damage. Even then, experts say, it would take hundreds of kilos of explosives, at a minimum, to break the dam.
An external detonation by a bomb or missile would exert only a fraction of its force against the prey, and an explosive many times greater would be needed to achieve a similar effect.
"The carrying capacity of a warhead is limited," says Nick Glumac, an engineering professor and explosives expert at the University of Illinois at Urbana-Champaign.
"Even a direct hit may not wipe out the dam."
"It takes a lot of energy," he says.
"The forces acting on the structure are immense. We have the force of water, which is huge. This is not like holding on to a thread; These things are hard."
During more than a year of heavy fighting, the Kakhovka dam has been repeatedly damaged, with each side accusing the other of bombing it.
The Russians captured it last year as they advanced toward the Dnipro and beyond, but months later the Ukrainians drove Russian forces from the west bank, turning the river — and the dam — into part of the border between the warring sides.
The Russians clung to the dam.
It is not clear, however, that the damage sustained by the dam was sufficient to cause it to rupture.
"Dams fail; it's absolutely possible," said Gregory B. Baecher, an engineering professor at the University of Maryland and a member of the National Academy of Engineering who has studied dam breaks.
But, he said, "I look at this and say, 'Gee, this looks suspicious.'"
In August, a Ukrainian rocket hit the dam's causeway.
In November, as Russian forces retreated across the river, an explosion destroyed part of the road; after that, images verified by The New York Times showed damage to some of the gates that let water through. But there was no indication of damage to the underlying structure.
Since November, the gantry cranes that open and close the gates have barely moved, though it was unclear if they hadn't been working.
This led first to unprecedented low water levels and then, as winter thaw and spring rains flowed into the reservoir upstream, to a record water level in 30 years.
Since the beginning of May, the water has risen above the floodgates and has exceeded the crest of the dam.
Satellite images taken last week showed more of the road missing; It is unclear whether it was swept away by the current or destroyed by a blow.
Some dams have collapsed due to the "overflow" of unusually high flows.
"Normally, such a break would start in the dirt part of the dam, on either of its banks," explains Professor Baecher.
Evidence
But photos and videos show that the Kakhovka dam first broke in the center, next to the power plant adjacent to the Russian-controlled shore.
At first, both ends seemed intact, but as the day progressed, the dam was collapsing more and more.
A combination of damaged sluice gates and high water could rip off some sluice gates, but it wouldn't be expected to destroy much of the dam, the professor said.
On Sunday, Ukraine appeared to launch a long-awaited counteroffensive against Russian forces, with officials saying Moscow blew up the dam to hinder their advance, causing flooding and eliminating the only remaining river crossing between the enemies.
It is unclear, however, whether Ukraine's plans go through a major crossing of the lower Dnipro.
Ukrainians wondered why they would want to destroy their own infrastructure, cities and farms, while noting that these have been frequent targets in Russia's brutal conduct of the war.
Moscow wanted to "show that it is ready for anything" if Kiev aggressively pursues its counteroffensive, said Roman Kostenko, chairman of the Ukrainian parliament's defense and intelligence committee.
"They do everything they can to stop our counterattack."
Kremlin spokesman Peskov said Ukraine had destroyed the dam to cut off the flow of water through a canal from the Dnipro to the Crimean peninsula.
After Russia illegally annexed Crimea in 2014, Ukraine halted the flow, but Russia resumed it last year after seizing the dam.
Other Russian officials claimed the attack was intended to support a Ukrainian offensive they said was failing, possibly to allow Kiev to reposition some forces or for floodwaters to push back Russian artillery near the river.
Some Western military analysts were wary of trying to quickly blame anyone, or even say whether the dam collapse was intentional.
"It's too early to tell," said Michael Kofman, director of Russian studies at CNA, a research institute in Arlington, Virginia.
The disaster, he said, "ultimately benefits no one."
Contributed by Riley Mellen, Haley Willis, Thomas Gibbons-Neff, Paul Sonne, Andrew E. Kramer, Matthew Mpoke Bigg, Eric Schmitt and Victoria Kim.
James Glanz is a journalist for the International section. He previously worked in the Research section and was head of the Baghdad office. He holds a Ph.D. in astrophysics from Princeton University and joined the Times as a science editor. @jamesglanz
Marc Santora reports from Ukraine since the beginning of the war with Russia. He previously worked in London as an international news editor focusing on breaking events and before that was head of the Central and Eastern Europe bureau, based in Warsaw. He has also done numerous reports from Iraq and Africa. @MarcSantoraNYT
Richard Perez-Peña, an international news editor in New York, has worked at The Times as a reporter and editor since 1992. He has worked in the newsrooms of Metro, Nacional, Negocios, Medios and Internacional. @perezpena - Facebook
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