Liquidation is determined by borrow collateral factors (used to determine initial borrowing capacity).
When an account’s borrow balance exceeds the limits set by collateral factors, it is eligible for liquidation. A liquidator (a bot, contract, or user) can call the absorb function, which relinquishes ownership of the accounts collateral, and returns the value of the collateral, minus a penalty (liquidation factor), to the user in the base asset. The liquidated user has no remaining debt, and typically, will have an excess (interest earning) balance of the base asset.
Each absorption is paid for by the protocol’s reserves of the base asset. In return, the protocol receives the collateral assets. If the remaining reserves are less than the target, liquidators are able to buy the collateral at a discount using the base asset, which increases the protocol’s base asset reserves.