PALU, Indonesia—On a break from Bible study at a church compound outside this city last week, Douglas Simamora was playing soccer with fellow students when the solid ground beneath his feet turned to liquid.
Mr. Simamora and his friends, attending a retreat with dozens of students and teachers, watched as the narrow A-frame Protestant church, with its steeple and image of Christ with hands outstretched over the doors, was swept away.
...