If this red mixture is spewing out occasionally, and it's coming from the lake, how exactly is the bacteria colony in the lake "isolated for 1.5 million years"?

If this red mixture is spewing out occasionally, and it's coming from the lake, how exactly is the bacteria colony in the lake "isolated for 1.5 million years"? It seems to me that there is potentially a path for flowing liquid connecting the lake to the front of the glacier. The alternative would be that the glacier occasionally picks up material from the top of the lake and slowly transports it as a separate mass to the front of the glacier where it gets released. Have radar studies of the glacier been done to determine its internal structure and the transport mechanism?