As winter turns to spring IRL, the two most popular cryptocurrencies are blooming as well.

Over the last week, both Bitcoin and Ether are up about 16%, after a rocky start to the month (and year). On Monday, both of the major cryptocurrencies got a boost, with Bitcoin up 6.2% and Ether up 6.8%, according to CoinMarketCap. Bitcoin was trading at $47,630 and Ether was trading at $3,387 as of Monday morning.

The two biggest cryptocurrencies are trading at prices not seen since the first days of January The last few months have been referred to as a crypto winter, after Bitcoin fell to a low of about $33,184 and Ether to a low of $2,455 in late January. But that could be changing. On Monday, Bitcoin was up about 43.5% and Ether was up 37.9% from 90-day lows.

Smaller cryptocurrencies like XRP, Cardano, Avalanche, and Solana also saw increases over the weekend. Of those currencies, Solana experienced the biggest daily jump of more than 10% since Sunday, and was up 22% over the past week.

The spike in prices could be attributed to a number of factors, though there’s not one clear explanation.

For Bitcoin, a commitment by the cofounder of a major crypto company to purchase billions of the currency in the near future could have pushed prices higher. Do Kwon, the founder of decentralized finance company Terraform Labs, which created two stablecoins tied to the price of the U.S. dollar, said on March 14 that he would be buying $10 billion in Bitcoin to back up the reserves for the company’s terraUSD (UST) stablecoin. Unlike other stablecoins, UST does not have a 1:1 reserve of dollars for every token it issues, by buying Bitcoin as reserves, the stablecoin is more likely to hold its value.

Investors in Ether could be feeling bullish due to an upcoming update in the crypto’s underlying technology called the “merge” that could make it more environmentally friendly and introduce new revenue streams for the crypto-savvy. That update would also transform Ether from a “proof of work” blockchain, to “a proof of stake” blockchain.

Making Ether proof of stake would eliminate the need for crypto mining, which uses high-powered, energy sucking computers to verify transactions on the blockchain. It could reduce the energy consumption of the Ethereum blockchain, and Ether, by as much as 99%, according to the Ethereum Foundation, a nonprofit organization which supports the technology.

As Russia’s invasion of Ukraine continues, Ukraine has also opened its arms to cryptocurrencies. The country has been receiving millions in donations in crypto, and passed a bill late last month legalizing digital assets.

This story was originally featured on Fortune.com