First of all, we should know where these bonded capital come from. In thorchain, to be able to run a node, you need to bond a certain amount of Rune. this is the only source and one of two main variables in keeping security and functionality of network. But nodes will add up and subtract the amount they bonded over time based on different reasons like market situation or risk management. also new nodes come and old ones reside, they all are incentivized to bond more rune since they might be eliminated if someone with more bonded rune comes in.

This chart shows total bonded rune subtracted by returned rune each day. as it is obvious total bonded amount is increasing everyday and it's more than 50M lately.