A prominent structure on Kīlauea's southern flank is the Hilina fault system, a highly active fault slipping vertically an average of per year along the system. Its physiographic province is deep, but it is unknown whether it is a shallow listric fault or if it penetrates to the very base of the volcano. In connection with the 2018 lower Puna eruption the Hawaiian Volcano Observatory published some facts leading to the conclusion, that a catastrophic collapse would be incredibly remote. A number of cinder cones, satellite shields, lava tubes, and other eruptive structures also dot the volcano, evidence of its recent activity. Kīlauea has some interactions with Mauna Loa, its larger neighbor and only other recently active volcano on the island; interspersed lava flows and ash deposits belonging to its neighbor have been found on its flanks, and some of Mauna Loa's flows are, in turn, blanketed in Kīlauea tephra. In particular, the saddle between the two volcanoes is currently depressed, and is likely to fill over in the future.