Historical eruptions at Mauna Loa are typically Hawaiian in character and rarely violent, starting with the emergence of lava fountains over a several kilometer long rift colloquially known as the curtain of fire (often, but not always, propagating from Mauna Loa's summit) and eventually concentrating at a single vent, its long-term eruptive center. Activity centered on its summit are usually followed by flank eruptions up to a few months distant, and although Mauna Loa is historically less active than that of its neighbor Kilauea, it tends to produce greater volumes of lava over shorter periods of time. Most eruptions are centered at either the summit or either of its two major rift zones; within the last two hundred years, 38 percent of eruptions occurred at the summit, 31 percent at the northeast rift zone, 25 percent at the southwest rift zone, and the remaining 6 percent from northwest vents. 40 percent of the volcano's surface consists of lavas less than a thousand years old, and 98 percent of lavas less than 10,000 years old. In addition to the summit and rift zones, Mauna Loa's northwestern flank has also been the source of three historical eruptions.