ABSTRACT Near Moku‘āweoweo, Mauna Loa’s summit caldera, there are three fans of explosive deposits. The fans, located to the west, northwest, and east, are strongly arcuate in map view. Along ‘Āinapō Trail, 2.8–3.5 km southeast of the caldera, there are several small kīpuka that expose a fourth explosive deposit. Although these explosive deposits have been known for some time, no study bearing on the nature of the explosive activity that formed them has been done. By analyzing cosmogenic exposure age data and the physical properties of the debris fans—lithology, size distributions, and clast dispersal—we conclude that the lithic deposits are the result of five separate phreatic events. The lithic ejecta consist of fragments of ponded lavas, pāhoehoe, gabbroic xenoliths, and “bread-crust” fragments. The exposure ages indicate that the explosive deposit on the west caldera rim was erupted 868 ± 57 yr B.P.; for the northwest fan, the age determination is 829 ± 51 yr B.P.; and on the east rim, ejecta deposits are younger, with ages of 150 ± 20 and 220 ± 20 yr B.P. Lavas underlying these deposits have exposure ages of 960–1020 yr B.P., consistent with the stratigraphy. Near ‘Āinapō Trail, the explosive deposit is much older, overlain by flows dated with a pooled mean age of 1507 ± 19 yr B.P. From the cosmogenic dating, we have three reliable and unambiguous dates. At a much earlier time, a fourth explosive eruption created the ‘Āinapō Trail deposit. We conclude there were at least five explosive episodes around the summit caldera. These deposits, along with recent work done on Kīlauea’s explosive activity, further discredit the notion that Hawaiian volcanoes are strictly effusive in nature. The evidence from the summit of Mauna Loa indicates that it, too, has erupted explosively in recent history.

Abstract Knowledge of variations in the extent and thickness of the Antarctic Ice Sheet is key for understanding the behaviour of Southern Hemisphere glaciers during the last ice age and for addressing issues involving global sea level, ocean circulation and climate change. Insight into past ice-sheet behaviour also will aid predictions of future ice-sheet stability. Here, we review terrestrial evidence for changes in ice geometry that occurred in the Ross Sea sector of Antarctica at the Last Glacial Maximum (LGM) and during subsequent deglaciation. During the LGM, a thick grounded ice sheet extended close to the continental shelf edge in the Ross Embayment. This ice reached surface elevations of more than 1000 m along the coast of the central and southern Transantarctic Mountains and Marie Byrd Land. The local LGM occurred by 18 ka on the coast, but as late as 7–10 ka inland. The first significant thinning took place at roughly 13 ka, with most ice loss happening in the Holocene. This history makes it unlikely that the Ross Sea sector was a major contributor to meltwater pulse 1A (MWP 1A). Resolution of a possible Antarctic origin for MWP 1A awaits detailed reconstructions from all sectors of the ice sheet.