Fees on a public blockchain can multiply within minutes and fall back just as fast. The volatility comes from a supply that cannot expand to meet demand.
Block space is a fixed-supply auction
A blockchain adds blocks at a roughly constant rate, and each block holds a limited quantity of transaction data. That capacity does not increase when more people want to transact.
Transactions waiting to be included sit in a queue, and those offering higher fees are selected first. The arrangement is an auction for a scarce, perishable good.
Because supply is fixed in the short term, the entire adjustment to a demand surge has to happen through price. There is no other release valve.
Demand arrives in bursts rather than steadily
Activity on these networks is event-driven. A popular token launch, a liquidation cascade or a sudden price move can send thousands of transactions into the queue at once.
Many of those transactions are time-sensitive, submitted by participants who lose money if inclusion is delayed. They bid aggressively rather than waiting for calm.
Automated systems compound the effect, since bots respond to the same trigger simultaneously and compete against each other for position within the next block.
Fee estimation is a forecast, not a quote
Wallets suggest a fee by examining what recent transactions paid and what is currently queued. That is a projection based on conditions that already existed.
When demand changes faster than the estimate updates, a transaction submitted at the suggested rate can sit unconfirmed while later ones with higher fees pass it.
Some networks allow a stuck transaction to be replaced with a higher-fee version, and some do not. Where replacement is unavailable, waiting is the only option.
Congestion tends to feed on itself
As the queue lengthens, participants raise their bids to avoid being stuck behind it, which raises the clearing price for everyone including those who were not in a hurry.
Failed and replaced transactions add further load, since each attempt consumes capacity whether or not it ultimately succeeds.
The spiral breaks when the triggering event passes and the backlog clears, which is why extreme fee periods are usually short rather than sustained.
Scaling layers change where the pressure lands
Secondary layers process transactions away from the main chain and periodically post compressed summaries back to it, so many transactions share the cost of one settlement.
This lowers the per-transaction cost substantially, but the underlying constraint remains, and congestion on the base layer still raises costs on the layers built above it.
Fee spikes therefore become smaller and less frequent rather than disappearing. The auction for base layer capacity continues to set the floor for everything above.