Semeru Volcano Erupts in Indonesia. On November 19, Semeru Volcano erupted in Indonesia, prompting the country's volcanology agency to raise the alert level for Java's highest mountain to the highest. The volcano erupted with ash clouds reaching 5.6 kilometers (19.5 miles), warning residents to stay 2.5 kilometers (1.5 miles) away due to the risk. Semeru, over 3,600 meters (11,200 feet) tall, is one of nearly 130 active volcanoes in Indonesia. Indonesia is located on the Pacific Ring of Fire, a highly seismic zone where different crustal plates meet, resulting in a high number of earthquakes and volcanic eruptions.