Volcano Watch — Sometimes, Volcanoes Need to be Left Alone

Park manager Horacio Herrera assured everyone that the closure was precautionary and not due to any particular incidents. The park has been closed before, he said. Although Turrialba is very different than Kīlauea, the elevated emission story is familiar to Hawai`i Island residents.

Turrialba and its twin, Irazu Volcano, located about 10 km to the west, share a common base, and they are the southernmost volcanoes in Costa Rica. The peak of Turrialba Volcano contains three craters and rises about 3,340 m (11,000 ft) above flanks covered by dense tropical forest. This volcano is so remote that it is only accessible via a 4WD trail. Google Earth doesn't even have high resolution imagery of it.

Turrialba Volcano has had at least six major explosive eruptions in the last 3,400 years. The volcano's most recent eruption was in 1866, but signs of reawakening started several years ago. Seismicity began increasing in the late 1990s, and fumarolic activity became pronounced a few years later. SO₂ emission rates, measured in the same way that they are measured in Hawai`i, increased from about 140 tonnes/day in late 2007 to 1,100-2,000 tonnes/day in summer 2008.

Because Turrialba Volcano is surrounded by vegetation, the increase in SO₂ emissions has dramatic effects no matter what the wind direction. The nearest residences are little more than 1.5 km (1 mile) south and southwest of the vents. The nearest town is also called Turrialba 16 km (10 miles) to the southeast and the capitol, San Jose, is 36 km (22 miles) to the west. Effects at Turrialba and San Jose are unknown.

A seasonal shift in winds in August and September blew these emissions to the south and southeast, resulting in vegetation being burned to the soil within 3 km (2 miles) of the west crater vent. The winds are not expected to shift back until later this month. Last year, local farmers voluntarily evacuated from the same area.

Unlike Turrialba, Kīlauea volcano is emitting gases at two main vents. Under normal trade wind conditions, Pu`u `Ō`ō emissions impact remote ohi`a forest in Hawai`i Volcanoes National Park most intensely; Halema`uma`u emissions blow into the Ka`u Desert. The nearest downwind community is Wood Valley, 26 km (16 miles) away. But when our winds are southerly, the nearest communities are those of Volcano Golf Course, Volcano Village, and Mauna Loa Estates 3-6 km (2-4 miles) from Halema`uma`u and communities from Fern Acres to Hawaiian Acres (Glenwood and Mountain View) 6-12 km (4-8 miles) from Pu`u `Ō`ō.

We are all familiar with the more distant effects of vog in Hawai`i and expect that it might be the same for Costa Ricans downwind of Turrialba Volcano. There is one important difference in the Turrialba emissions - they are released from the ground at an elevation of more than 3,000 m (10,000 ft), whereas the Halema`uma`u and Pu`u `Ō`ō emissions are released at elevations of 1,030 m (3,380 ft) and 700 m (2,300 ft), respectively.

The lower elevation of emission from Kīlauea traps the gases below the thermal inversion layer at around 2,000 m (6,500 ft) above sea level. The confinement results in the gases travelling farther from the source in higher concentrations. The higher elevation of Turrialba's emissions may mean that those gases will dissipate more thoroughly before reaching more distant residents.

In any case, Hawai`i Island residents are in a good position to empathize with Costa Ricans affected by Turrialba's increasing emissions.

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Volcano 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. On September 26, scientists got another look at the lava lake deep within the vent on the floor of Halema`uma`u. The lava lake, barely visible from the air, appeared to be deeper than when last seen on September 5. The lake surface is estimated at 120 to 150 m (about 400 to 500 ft) below the vent rim, and cannot be seen from the rim of Halema`uma`u Crater or Jaggar Museum Overlook. There have also been several small ash-emission events from the vent, lasting only minutes, in the last week.

Pu`u `Ō`ō continues to produce sulfur dioxide at even higher rates 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 fissure D of the July 21, 2007, eruption and flows toward the ocean through a well-established lava tube. The ocean entry at Waikupanaha continued unabated in the past week and has hosted frequent, small littoral explosions where the lava meets the water.

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 or call 961-8093 for viewing hours.

Mauna Loa is not erupting. Two earthquakes were located beneath the summit this past week. Continuing extension between locations spanning the summit indicates slow inflation of the volcano.

Three earthquakes beneath Hawai`i Island were reported felt within the past week. A magnitude-2.8 earthquake occurred at 11:25 a.m., H.s.t., on Friday, September 26, 2008, and was located 2 km (1 mile) southeast of Pahala at a depth of 8 km (5 miles). A magnitude-3.1 earthquake occurred at 8:18 p.m. on Saturday, September 27, 2008, and was located 7 km (4 miles) northwest of Kailua at a depth of 33 km (20 miles). A magnitude-2.6 earthquake occurred at 3:09 p.m. on Tuesday, September 30, 2008, and was located 6 km (4 mile) north of Ka`ena Point at a depth of 8 km (5 miles).

Visit our Web site for daily Kīlauea for 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.