November 26, 2008

A weekly feature provided by scientists at the Hawaiian Volcano Observatory.

Laki and Eldgjá—two good reasons to live in Hawai`i

Laki or Lakagígar (Craters of Laki) is a volcanic fissure situated in the south of Iceland, not far from the canyon of Eldgjá and the small town Kirkjubæjarklaustur, in Skaftafell National Park.

For those of us who live in East Hawai`i, having an active volcano in our back yard is a part of daily life. For nearly three decades, lava has been erupting from fissures on Kīlauea's east rift zone and flowing to the ocean, and, unless something big and exciting happens, this activity is not something that most of us (outside HVO) think about on a daily basis. Even with the addition of a summit eruption at Kīlauea, active now for the last eight months, we are, at the very least, becoming familiar with the extra volcanic gas that the volcano has been spewing out.

Though Kīlauea's ongoing eruption has been a source of much destruction over the years—burying entire communities and displacing hundreds of people—we are fortunate that this volcano allows us the luxury of forgetting that we live on an active volcano for months at a time. We are afforded this luxury only because most of Kīlauea's eruptions are, in a relative sense, fairly benign. Since the current east rift zone eruption began, Kīlauea has erupted, on average, about 4.1 cubic meters (5.4 cubic yards) of lava each second. That is equivalent to about two pickup loads of lava every second, and may sound like a lot until we take a look at two of history's great effusive eruptions—the Eldgjá and Laki eruptions in Iceland.

For eight months during the years 1783-1784, lava erupted from dozens of vents along a 27-km-long (17-mile-long) fissure system in the highlands of southern Iceland. Basaltic lava flows—just like the flows we see here in Hawai`i—poured south out of the mountains onto the coastal plains, burying 599 square km ( 231 square miles) in the process. The total volume of lava erupted in eight months is estimated at 15.1 cubic km (3.6 cubic miles). In comparison, Kīlauea's ongoing east rift zone eruption, approaching the end of its 26th year of activity, has produced only about 3.4 cubic km (0.8 cubic miles) of lava.

In addition to these enormous lava flows, eruptive episodes from the Laki fissure started with explosive eruptions that blanketed more than 8,000 square km (3,089 square miles) with volcanic ash and cinders. And if you think the vog here can be bad, Laki pumped out 122 million tons of sulfur dioxide in eight months. Compare this to Kīlauea's 0.85 million tons from February to September, 2008—less than one percent of Laki's output over the same length of time. Half of the livestock in Iceland died after eating grass contaminated with fluorine from the gas plume, and 20 percent of Iceland's population starved during the famine that followed. The sulfur dioxide released led to crop failures throughout Europe and may have led to, or exacerbated, other famines in the northern hemisphere that occurred at about the same time.

As large as the Laki eruption was, it was exceeded by Iceland's A.D. 934-940 Eldgjá eruption, which occurred in the same mountainous region of Iceland. During the six years that this eruption was active, lava erupted from several vents along a discontinuous 75-km-long (47-mile-long) fissure system and buried more than 781 square km (302 square miles) of southern Iceland. That is like burying all of Kīlauea east of Pu`u `O`o beneath lava. The total volume erupted was about 19.5 cubic km (4.7 cubic miles), or roughly equivalent to 163 years of continuous output at Kīlauea at its current eruption rate.

In terms of gas output, the Eldgjá eruption was the largest producer of volcanic gas in historic time, releasing 219 million tons of sulfur dioxide into the atmosphere. Though historical records are harder to come by for this eruption, its effects were likely as devastating to Iceland's people and livestock as the Laki eruption several centuries later.

Fortunately, huge eruptions like those at Eldgjá and Laki are very unusual; otherwise, life as we know it probably would not be. Though the hazards posed by lava flows and volcanic gas here on the Big Island are understandably important to us, they are still tiny in comparison to what our big blue planet is capable of. So, the next time Kīlauea's lava flows hit the news, or vog blankets your favorite community, think of Laki and Eldgjá and be thankful you live in Hawai`i.

Activity update

Kīlauea Volcano continues to be active. A vent in Halema`uma`u Crater is erupting elevated amounts of sulfur dioxide gas and very small amounts of ash. Resulting high concentrations of sulfur dioxide in downwind air have closed the south part of Kīlauea caldera and produced occasional air quality alerts in more distant areas, such as Pahala and communities adjacent to Hawai`i Volcanoes National Park, during kona wind periods. The have been several small ash-emission events from the vent, lasting only minutes, in the last week. Episodic tremor returned during mid-week resulting in fluctuations in vent glow after dark.

Pu`u `Ō`ō continues to produce sulfur dioxide at rates higher than the vent in Halema`uma`u Crater. Trade winds tend to pool these emissions along the West Hawai`i coast, while Kona winds blow these emissions into communities to the north, such as Mountain View, Volcano, and Hilo.

Lava continues to erupt from the Thanksgiving Eve Breakout (TEB) vent and flows toward the ocean through a well-established lava tube. The Waikupanaha ocean entry continues to build a small delta, the front of which is now visible from the County viewing area. A western branch of the tube, which diverges from the main TEB tube at the top of the pali, also continues to supply lava to breakouts on the coastal plain. These breakouts are scattered along the western margin of the TEB flow field and are slowly marching southward toward the National Park boundary.

Be aware that active lava deltas can collapse at any time, potentially generating large explosions. This may be especially true during times of rapidly changing lava supply conditions. Do not venture onto the lava deltas. Even the intervening beaches are susceptible to large waves generated during delta collapse; avoid these beaches. In addition, steam plumes rising from ocean entries are highly acidic and laced with glass particles. Check Civil Defense Web site (http://www.lavainfo.us) or call 961-8093 for viewing hours.

Mauna Loa is not erupting. One earthquake was located beneath the summit this past week. Continuing extension between locations spanning the summit indicates slow inflation of the volcano.

One earthquake beneath Hawai`i Island was reported felt within the past week. A magnitude-2.6 earthquake occurred at 7:02 p.m., H.s.t., on Saturday, November 22, 2008, and was located 7 km (4 miles) southeast of Captain Cook at a depth of 10 km (6 miles).

Visit our Web site (http://hvo.wr.usgs.gov) for daily Kīlauea eruption updates, a summary of volcanic events over the past year, and nearly real-time Hawai`i earthquake information. Kīlauea daily update summaries are also available by phone at (808) 967-8862. Questions can be emailed to askHVO@usgs.gov.