JAKARTA—Indonesia’s Mount Sinabung volcano sent a cloud of hot ash as high as 3.1 miles on Tuesday, in its first big eruption since August last year, the country’s volcanology center said. Mount Sinabung’s activity has increased since last year and the alert for the volcano in North Sumatra province has been placed at the second-highest level. No casualties were reported, but an official had earlier urged people to stay at least 1.8 miles from the crater, Indonesia’s Volcanology and Geological Hazard Mitigation Centre said. Videos on social media showed little panic among residents over the eruption, which sent a column of white ash into the blue sky. Wirda Br Sitepu, a 20-year-old resident, told Reuters that the situation had calmed and said “the mountain is not erupting, and the ash has decreased.” Indonesia straddles the so-called “Pacific Ring of Fire,” a highly seismically active zone, where different plates on the …