Walk around Emerald Lakes on the Tongariro Circuit, steam eruptions waft the air with a rotten egg gas smell of geothermal activity. Over the past 2,000 years the steam eruptions have widened the Red Crater and created the explosion craters that are now called Emerald Lakes. Dissolved minerals give the water its distinctive colours. Where water meets hot volcanic rocks, fumeroles or steam vents rise, and the ground is unstable.
