January 31, 2002
A weekly feature provided by scientists at the Hawaiian Volcano Observatory.
Nyiragongo -- Could it happen here?
At dawn on January 17, 2002, the residents of Goma, a city of 500,000 along the eastern border of the Republic of Congo, awoke to glowing red skies and falling ash. A large eruption of Mount Nyiragongo was underway, the first since 1977. Over the next 48 hours, lava flows exiting from three different fissures spilled over the countryside, destroying 14 villages and eventually entering Goma itself. At its widest, the flow that cut into Goma was more than 60 meters (200 feet) across.
The heat of the lava ignited buildings along the periphery of the flow and, within hours, fires were spreading throughout the city. Early reports suggest that nearly half of the buildings in Goma were either damaged or destroyed. By January 19, the eruptive activity was largely over, but large earthquakes are continuing to this day, and new fissures have opened on the outskirts of Goma. In the aftermath, more than 40 people were burned to ashes and hundreds of thousands found themselves homeless.
The 1977 eruption of Nyiragongo bears many similarities to this current eruption. It, too, began suddenly and with little warning, involved major crater floor collapse, and culminated in voluminous and fast moving lava flows. Unlike the recent eruption, however, the lava flows did not reach Goma. Because of the extremely high speeds of the 1977 lava flows, estimated by some observers to peak at 100 km/hr (62 mph) on Nyiragongo's steep upper slopes, the death toll from the 1977 eruption was staggering. Some reports put the number killed in the thousands. Exact numbers will never be known. The fast-moving flows swept through rural villages in the middle of the night, catching the villagers unaware and, in most cases, asleep.
Residents of Hawai`i, no strangers to volcanic activity and the destruction it often brings, may still wonder if such rapid and sudden catastrophes could strike here. Though we can never be certain about the future, the short answer to this question is still probably "no." There are two main reasons why Hawai`i residents need not fear a Nyiragongo-like cataclysm. First, the nature of Hawai`i's volcanoes, though similar to Nyiragongo in some ways, has several important differences. Second, hundreds of instruments operated by many scientists keep a careful watch over the local volcanoes. Taken together, these two factors virtually assure that Hawaiians need not fear sudden lava flows entering populated areas without warning.
The chemical composition of the Nyiragongo lava is unusual, almost unique. Nyiragongo lava contains very little silica. This makes it highly fluid and capable of flowing at very great speeds. Hawaiian lava also contains only modest amounts of silica, but still enough to limit flow velocity to about walking speed in most cases. Only when lava moves down very steep slopes can it move very fast, and then only when the effusion rate is high. But, most slopes on Hawaiian volcanoes are gradual, in contrast to Nyiragongo, which has built a steep and dramatic cone. Moreover, Nyiragongo is prone to radial fissures that can open suddenly on its lower slopes.
Until the recent eruption (and prior to the 1977 eruption) an active lava lake sat within Nyiragongo's crater. The danger here is easy to see: a large reservoir of very fluid lava perched above a populated area and contained only by a potentially leaky cone. Conditions like these exist nowhere in Hawai`i, and if they ever do occur, scientists at HVO would begin vigilant monitoring that would not end until the dangerous conditions abated.
The greatest volcanic dangers facing Hawai`i residents are on the populated west slopes of Hualalai, the southwest slopes of Mauna Loa, and along Kilauea's east rift zone in lower Puna. Eruptions at Hualalai's summit or Mauna Loa's southwest rift zone could send lava flows into populated regions within hours and, for Kilauea's east rift zone, within minutes. Still, this lava would not be moving at great speed, and seismic monitoring, combined with GPS and tiltmeter observations, would almost certainly have anticipated an imminent eruption. Thanks to the relatively benign nature of most Hawaiian volcanism and to the efforts of HVO, the primary victim of Hawaiian lava flows will remain property rather than people.
Eruptive activity of Kilauea Volcano continued unabated at the Pu`u `O`o vent during the past week. The two shields built over the main tube system above Pulama pali are still topped with active lava ponds. Overflows from the ponds feed short, multidirectional flows radial to the shields. No molten lava was observed descending Pulama pali or flowing in the coastal flats during an overflight on January 31. Heavy rainfall earlier in the week obscured most visual observations of flow activity. The ocean entry at Kamoamoa stopped some time after the morning of January 29 when it was last seen active. Lava is not entering the ocean anywhere along the coastline.
Updated: February 4, 2002 (pnf)