Hawaii is a volcanic island. It’s no surprise, therefore, that its volcanoes (eight are listed on the Smithsonian Institution/National Museum of Natural History’s Global Volcanism Program database) have done more than just build the islands – but continue to influence the shape of the landscape and the lives of those who live there.
The typical eruption of a Hawaiian volcano involves relatively thin lava which flows – rather than the more viscous, explosive lavas associated with some of the great eruptions such as those of Vesuvius or Krakatua.
Typically, these eruptions occur along linear cracks, or fissures, in the crust and can spill out vast quantities of lava generating extensive lava fields; a current example of such a fissure eruption is the ongoing event at Holuhraun, in Iceland.
The Ongoing Eruption of Kilauea
At 1222 metres, Kilauea is very much the little sister of its neighbour, Mauna Loa; but it has the distinction of being what volcanologists Peter Francis and Clive Oppenheimer describe as “the most continuously active volcano on Earth; lava streaming into the ocean at a steady rate of around 5 for years on end.”
The current eruption, which is making the news as it threatens local homes, is a case in point. Known as the Puʻu ʻŌʻō eruption, it’s been bubbling quietly away for over 20 years — since January 1983, in fact. According to the Hawaii Volcano Observatory (HVO) it is “the most voluminous outpouring of lava from the volcano’s East Rift Zone in the past five centuries.”
And the statistics are mind-boggling: “By December 2012, flows had covered 125.5 km2 (48.4 mi2) with about 4 km3 (1 mi3) of lava, and had added 202 hectares (500 acres) of new land to Kīlauea’s southeastern shore. Lava flows had also destroyed 214 structures, and resurfaced 14.3 km (8.9 mi) of highway, burying them with as much as 35 m (115 ft) of lava.”
The June 27 Lava Flow
Such long-lived eruptions go through phases. The current phase involves a lava flow which began in June and which has subsequently extended north westwards in a narrow lobe until it threatened the settlement of Pahoa; It was first declared a ‘potential concern’ in an HVO news release on 22 August.
The lava finally reached the village on 28 October, having flowed across the village cemetery.
At the time of writing there were no reports of any properties having been destroyed and the lava flow seems to have stalled. Nevertheless, on 1 November Hawaii’s Civil Defense organisation issued a notification that: “based on the current flow location, direction and advancement, residents in the flow path were placed on an evacuation advisory and notified of a possible need for evacuation.”
Direct contact with lava is just one of many potential hazards associated with volcanism; although the characteristically gentle eruption of Hawaii’s volcanoes means that many are of relatively limited significance. Volcanic eruptions produce significant amounts of gas (although both the volume and the nature of the gases vary) and these can be significant.
Kilauea’s current eruption is producing some sulphur dioxide gas but it appears significant only locally, emitted from the eruptive vent rather than from the surface of the lava flow itself. The HVO’s daily update for 1 November warned that: “potentially-lethal concentrations of sulfur dioxide can be present within 1 km downwind” but the most recent Civl Defense alert makes no mention of gas.
Hawaii: a Volcanic Land
Like Iceland, Hawaii is created by volcanoes but it differed in that more of its settled areas are vulnerable to destruction by lava flows. Hawaii has been boiling quietly away for millions of years and it isn’t going to stop now — even if the current lava flows stalls and the homes in Pahoa survive.