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These missing rocks can add up to entire missing landscapes: beyond Earth, you’d have a tough time finding anything like the limestone columns of Hạ Long Bay, a stratovolcano like Mt.

The stratovolcano, which is located 750km south of the capital, has been active for about 650,000 years.

The Nevado del Ruiz is a stratovolcano or composite volcano.

The Nevado del Ruiz is a stratovolcano, or composite volcano, which straddles the border between Colombia's Tolima and Caldas provinces.

It would be like Mount St. Helens, a steep stratovolcano that can erupt explosively, sending dirt, rock and sodium into the atmosphere, erupting on Earth, rather than Mauna Loa, a gently-sloped shield volcano that erupts with liquid lava flows.