> The rocks beneath our feet showed incandescent glows deep in the cracks, and we started to smell burned rubber from our cheap tennis.

When I was there, this happened in the area that the rangers guided us to. There was an active flow of pāhoehoe at the time, which we could get as close to as we wanted - the heat was a strong disincentive to doing anything dumb. We were warned at the start that shoes with rubber soles would be ruined, but that warning was too late for me and I had no alternative. It was certainly worth the price of a pair of sneakers though.