Are Piton de la Fournaise (La Réunion) and Kīlauea (Hawai‘i) really “Analog Volcanoes”?

The basaltic ocean island volcanoes of Kīlauea (Island of Hawai‘i) and Piton de la Fournaise (La Réunion Island) are remarkable natural laboratories for volcanology. Both are near the active ends of long hotspot chains and host frequent eruptive activity (both effusive and explosive). Investigations of the geophysical, geochemical, and geologic manifestations of volcanism at the two locales provide insights into a variety of processes, from the supply of magma to its eruption at the surface. The oft-stated claim that Kīlauea and Piton de la Fournaise are “analog volcanoes” appears well founded, at least in part. The two volcanoes share similar characteristics with regard to magma plumbing, occurrence of flank instability, structural and compositional evolution, and eruptive activity. Noteworthy differences include the size of the edifices (Kīlauea is about an order-of-magnitude larger in volume), their life spans (Piton de la Fournaise has been active for twice as long), and flank instability mechanisms. These differences are attributable to Hawai‘i's higher magma supply from and faster plate velocity relative to the hotspot compared to Piton de la Fournaise. Understanding these similarities and differences can be used to leverage studies of processes at one volcano by exploiting their occurrence or absence at the other.