Mauna Loa is a shield volcano that covers half of the Big Island. Its mass is so immense that it physically depresses the ocean floor beneath it by about 5 miles.

This name perfectly describes its structure, as its gently sloping, elongated shield stretches for roughly 74 miles across Hawaii's Big Island.

Instead of explosive eruptions of ash, Mauna Loa produces runny basaltic lava that travels vast distances before cooling, creating its gently sloping shield shape.

Perched at 11,000 feet, the observatory sits above local pollution layers, making it the ideal location to measure the continuous rise in atmospheric CO2 since 1958.