Satoshi-era coins waking up. This is 0.0008% of all volume ever recorded, so a spike is always an individual event and is usually reported as news the same day.
DefinitionValue of outputs spent whose age fell more than ten years. Age is real elapsed time off a monotonised block clock (the running maximum of block timestamps), not blocks divided by 144. The twelve bands sum to total spent output volume exactly.
LimitA single old wallet can create the entire spike, and a coin moving is not the same as a coin being sold. Age is per output, not per owner: consolidating coins or receiving change resets the clock on bitcoin nobody sold.