MOSCOW—Towering clouds of ash and glowing lava are spewing from two volcanoes on Russia’s Kamchatka Peninsula and scientists say major eruptions could be on the way.

The peninsula, which extends into the Pacific Ocean about 6,600 kilometers (4,000 miles) east of Moscow, is one of the world’s most concentrated areas of geothermal activity, with about 30 active volcanoes.

The sudden new activity followed a strong earthquake on Saturday, news reports said.

The Russian Academy of Sciences’ vulcanology institute said that at Klyuchevskaya Sopka, which at 4,754 meters (nearly 16,000 feet) is Eurasia’s tallest active volcano, as many as 10 explosions an hour were being recorded.

Lava flows and ash emissions also are coming from the Shiveluch volcano, the institute said.

Kamchatka is sparsely populated. The town of Klyuchi, with about 5,000 people, lies between the two volcanoes, 30–50 kilometers (20–30 miles) from each.

The volcanoes are about 450 kilometers (270 miles) from the peninsula’s only major city, Petropavlovsk-Kamchatsky.