Since no lava reaches the surface, it is called an intrusion. When magma evacuates a magma chamber, there is often no support for its roof rocks. The roof of the magma chamber literally caves in and creates a depression. The floor of the caldera is rapidly covered with new lava to create relatively flat and smooth topography. Pit craters form in a similar manner, but on a smaller scale, and they commonly develop over rift zones.
Summit calderas are indicative of the shield stage of Hawaiian volcanism.
In contrast, Mauna Kea's summit is more pointed than Mauna Loa's and is dotted with cones. Mauna Kea is in the post-shield stage, and its summit caldera has been filled by later eruptions. For those of you who have never been to the summit of Mauna Loa, envision three roughly circular depressions aligned in a northeast-southwest direction. Geologic evidence uncovered through field mapping indicates that Mauna Loa has formed several calderas in its life cycle. The most recent caldera formed during the interval between 1,000 and 1,500 years ago.