The Terra-LUNA Collapse Explained: Why the UST Algorithmic Stablecoin Failed

What happens if a coin you hold to use like a dollar suddenly drops below $1? It depends on whether the price is only wobbling for a moment or whether the assets backing your redemption have actually run short. The collapse of TerraUSD (UST) and LUNA in May 2022 showed this difference.

The key is that LUNA, which was minted to shrink the UST supply, collapsed along with it. The more people dumped UST, the more the LUNA supply grew, and the further LUNA's price fell, the more LUNA was needed to absorb the same amount of UST. A mechanism meant to restore the price ended up amplifying the collapse during a mass exodus.^{1Source 1U.S. Federal Deposit Insurance Corporation (FDIC), Can Stablecoins Be Stable?}

How did the UST-LUNA swap mechanism work?

A stablecoin is a cryptocurrency designed to track the price of a reference asset such as the US dollar. Keeping that price is called pegging, and drifting away from it is called a depeg. Instead of paying out dollars held in a bank, UST was an algorithmic stablecoin that tried to hold its price through swaps with LUNA.^{2Source 2Terra, About the Terra Protocol}

Under the design at the time, you could burn 1 UST and mint $1 worth of new LUNA. When UST traded below $1, the system counted on arbitrage: people buying cheap UST and swapping it for LUNA. Conversely, when UST traded above $1, LUNA would be burned and UST minted to increase supply.^{2Source 2Terra, About the Terra Protocol}

Ignoring swap fees, let's assume LUNA is priced at $10 each. Swapping 1 UST requires 0.1 LUNA, but if LUNA falls to $1, it takes 1 LUNA, and if it falls to $0.10, it takes 10. Even though the value created is the same $1, the lower LUNA's price goes, the more LUNA gets minted.

Here, "receiving $1 worth of LUNA" and "getting $1 in cash back" are two different things. The swap is only complete once you can sell the LUNA you received on the market, and LUNA's price keeps moving in the meantime. When a crowd rushes to sell both UST and LUNA, the swap mechanism that was supposed to restore the price struggles to hold up.^{1Source 1U.S. Federal Deposit Insurance Corporation (FDIC), Can Stablecoins Be Stable?}

Timeline of the May 2022 UST depeg and LUNA collapse

To understand the UST collapse, it helps to separate the initial price deviation from the chain reaction that followed. A price deviation that began on exchanges was compounded by deposit withdrawals and selling, and LUNA minting meant to shrink UST could not stop it.

• May 7, 2022: A series of trades on the decentralized exchange Curve pushed UST's price away from $1.
• May 7–9, 2022: Funds flowed out of Anchor Protocol, which was used for UST deposits, increasing downward pressure on the price.^{3Source 3Jump Crypto, The Depegging of UST}
• May 8–12, 2022: Luna Foundation Guard deployed reserve assets to try to defend UST's price, but failed to hold the $1 peg.^{4Source 4Luna Foundation Guard, report on transactions related to the UST peg defense}
• Around May 12, 2022: LUNA was minted at a rapid pace in the process of burning UST, and LUNA's price collapsed as well. UST and LUNA ended up amplifying each other's decline.^{1Source 1U.S. Federal Deposit Insurance Corporation (FDIC), Can Stablecoins Be Stable?}
• May 28, 2022: A separate new Terra chain launched. The original LUNA became Luna Classic (LUNC), and the original UST became USTC.

If you think of this event simply as "the program that kept the price in line stopped working," it's easy to miss the real cause. Even while the swap mechanism was running, it couldn't support the price if there wasn't enough demand to absorb the newly minted LUNA. The ability to execute code and the ability to maintain an asset's value in the market were two separate things.

The difference between the new LUNA and Luna Classic (LUNC)

If you come across "LUNA" in older articles or on a trading screen, start by identifying which chain the asset belongs to. The original chain at the time of the collapse remains as Terra Classic, and the LUNA on that chain is LUNC. LUNA on the new chain uses the same LUNA ticker, but it is a separate asset.

The new Terra chain launched without its own stablecoin system, including the original UST. The existence of a new LUNA does not mean the original UST's dollar redemption was restored. This is also why, when reading old wallet guides or transaction records, you shouldn't treat the LUNA of that time and the new chain's LUNA as one continuous asset.^{5Source 5Terra, dApp Migration Guide}

Fiat-backed vs. synthetic stablecoins

When looking at stablecoins after UST, it's easier to tell them apart by what backs their value rather than by their names. Fiat-backed stablecoins hold cash and cash-equivalent assets as reserves and support redemptions. USD Coin (USDC) uses this structure, and its reserves include bank deposits and short-term US Treasuries.^{6Source 6Circle, Transparency & Stability}

However, selling a coin on an exchange and requesting a dollar redemption from the issuer are different processes. Even with USDC, redeeming directly with the issuer requires meeting the conditions in its terms, such as having an account and being eligible. You should read "there are reserves" and "I can get cash right away" as two separate claims.^{7Source 7Circle, USDC Terms}

Ethena's USDe is a synthetic dollar. It is designed to maintain dollar value by combining crypto assets with positions such as short futures that profit when those assets fall in price. It differs from a structure like UST's, which minted its own linked token for swaps, and its current reserve management also includes lending and tokenized assets.^{8Source 8Ethena, Ethena Overview}

A strategy that reduces price volatility doesn't eliminate the possibility of losses. USDe's market price can also deviate from $1, and the value of its reserve assets can decline. You can read more about how synthetic dollars work in our earlier post "What Are Ethena and the USDe Stablecoin?", and about a separate example of a fiat-backed stablecoin in "What Is TrueUSD (TUSD), and Is It a Safe Stablecoin?".^{9Source 9Ethena, USDe Terms and Conditions}

The lesson of the Terra-LUNA collapse is clear. With a stablecoin, what matters more than the $1 target price is the assets you can get back and the structure that lets you actually receive them.