Bitcoin block times slow as US winter storm curtails mining

The clearest impact was visible at Foundry USA’s mining pool, where hashrate dropped by roughly 60% since Friday as miners powered down, an estimated reduction of nearly 200 EH/s. Even after the cutbacks, Foundry’s pool still held about 198 EH/s – roughly 23% of global mining-pool hashrate – underscoring how a concentrated pullback in a single pool can ripple into network-level block timing.

When a large slice of miners goes offline quickly, the network’s difficulty does not instantly adjust. Until the next difficulty retarget, the same proof-of-work threshold is being tackled by fewer hashes per second, so expected time-to-solve rises and blocks arrive more slowly. That shows up immediately in confirmation cadence and can widen the window for fee competition if transaction demand stays constant while blockspace arrives less frequently.

Real-time network indicators during the storm period reflected that slowdown. The mempool.space difficulty-adjustment page showed average block time running above 11 minutes at the time of tracking, alongside a projected downward adjustment (a negative estimate) if slower block intervals persisted into the retarget window.

Curtailments fit a familiar operating pattern for large North American miners, many of whom run flexible-load strategies and can reduce power consumption during grid stress events. TheMinerMag’s pool-level tracking also showed declines at other large pools over the same period, including Luxor, consistent with a broader regional pullback rather than an isolated outage.

Bitcoin’s protocol adjusts mining difficulty only once every 2,016 blocks, a process that typically spans about two weeks under normal conditions. When hashrate drops suddenly – as it did during the storm – block times lengthen immediately, but difficulty remains fixed until the next retarget, leaving the network temporarily operating below its intended cadence.

Many of the affected miners operate in US states with active demand-response programs, particularly Texas, where mining firms routinely curtail load during periods of grid stress in exchange for power credits or avoided pricing spikes. These programs allow miners to shut down within minutes, making weather events one of the fastest ways for large amounts of hashrate to leave the network at once.

Historically, similar weather-driven curtailments have produced short-lived effects on Bitcoin’s settlement layer. Once power conditions normalize and miners reconnect, hashrate typically rebounds quickly, and block times converge back toward the 10-minute target, with any residual imbalance corrected at the next difficulty adjustment.