In 1981 I was working in Medan, North Sumatra but as I was about to transfer to The Hague we decided to take vacation and travel around some other parts of Indonesia before leaving. We had just spent a few days in Yogyakarta and were now flying east to Bali over East Java and the Bromo Tengger Semeru National Park.

The islands of Sumatra and Java lie on a long volcanic arc above a subduction zone where the Indo-Australia plate is moving beneath the Eurasia plate making it very volcanically active.