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Mauna Loa's summit is also the focal point for its two prominent rift zones, marked on the surface by well-preserved, relatively recent lava flows (easily seen in satellite imagery) and linearly arranged fracture lines intersected by cinder and splatter cones.
The first is a 60 km (37 mi) rift trending southwest from the caldera to the sea and a further 40 km (25 mi) underwater, with a prominent 40° directional change along its length; this rift zone is historically active across most of its length.
Lava eruptions from Mauna Loa are silica-poor and very fluid, and they tend to be non-explosive.
It was created between 1,000 and 1,500 years ago by a large eruption from Mauna Loa's northeast rift zone, which emptied out a shallow magma chamber beneath the summit and collapsed it into its present form.Mauna Loa has been monitored intensively by the Hawaiian Volcano Observatory since 1912.