re: "Lava continues to flow beneath this hardened surface"
That's the past imperfect tense, describing times past as if they were current.
Lava continues to flow beneath this hardened surface for some time, developing flow tubes and tunnels. These can be reoccupied by numerous subsequent eruptions and become part of the volcanoe's lava delivery system.
No flow is occurring today.
Gerhard Neukum writes in a very stodgy German way and he has little sense of humour...