The views provided of the lunar (slide #24) and martian (slide #25) surfaces provide tantalizing glimpses of the meter-scale geology of these worlds. On both the Moon and Mars the landscapes are strewn with rocks ranging from millimeters to approximately 1 meter in diameter. Trying to find terrestrial analogs to these planetary rock fields is often difficult because of the nature of the fragmentation processes involved in the formation of ejecta blocks. The boulder field produced by the May 1924 eruption of Kilauea Volcano, Hawaii, provides one of these rare terrestrial analogs because an extensive boulder field was produced by the rapid fragmentation of basaltic rock during an explosive eruption. In this instance, a phreatomagmatic eruption of Halemaumau Crater fragmented preexisting volcanic country rock and scattered this material across the adjacent landscape in a process that was probably very similar to the formation and emplacement of ejecta blocks during an impact cratering event. This view of the rim of Halemaumau Crater shows many angular fragments that at first impression appear similar to the boulder fields seen at Taurus-Littrow and Utopia Planitia. The largest blocks seen in this view are approximately 1.2 meters in diameter.
Photograph courtesy of P. Mouginis-Mark.