The three volcanoes—Tongariro, Ngauruhoe and Ruapehu, which have resulted due internal tectonic processes, have erupted as recent as August 2012. The park has two other volcanoes on the northern end that last erupted over 20,000 years ago. These volcanoes have been together building the mountains of Tongariro National Park for over two million years.
Ruapehu is one of the world's most active volcanoes and the largest active volcano in New Zealand. The volcano began erupting at least 250,000 years ago, with major eruptions occurring about 50 years apart and minor eruptions almost every year. Between major eruptions, a beautiful emerald crater lake forms, fed by melting snow. Their brilliant colors are caused by dissolved minerals leaching from the surrounding rocks.
These lakes are popular viewpoints along the Tongariro Alpine Crossing—a celebrated one-day trek that traverses the otherworldly terrain along the slopes of all three mountains.
Mount Tongariro, Ruapehu and its surrounding area were one of the several locations used to shoot the Lord of the Rings trilogy, and the near-perfect conical shape of Ngauruhoe was the basis for Mount Doom.