April 17, 2008
A weekly feature provided by scientists at the Hawaiian Volcano Observatory.
Unfamiliar Tricks from our Familiar Volcano
A human lifespan is but a blink of an eye compared to Kilauea's 300,000-600,000 years of existence. Casual volcano watchers, being captives of the human experience, become accustomed to the type of activity Kilauea has exhibited during our brief lifetimes. We expect something similar to what we've seen before: the towering lava fountains, long lava flows, beautiful ocean entries, and churning lava lakes that have characterized the eruptions of the past decades.
What's missing from this list is explosive activity. We may not have seen much, but Kilauea is no stranger to large explosions. The eruption of 1790 produced enormous ash columns visible from Kawaihae, and even larger explosive eruptions occurred in earlier times.
Now that Halema`uma`u's mild explosive activity has gotten our attention, let's see how it stacks up in the scheme of well-known ash-generating eruptions.
One familiar and much more explosive volcano that provides an interesting comparison is Mount St. Helens. The May 18, 1980, eruption produced an ash column that reached over 18,000 m (60,000 feet, nearly twice the height of jet travel) within 10 minutes. Twenty-five cm (10 inches) of ash and pumice were measured 16 km (10 miles) downwind, and 5 cm (2 inches) of ash fell 320 km (200 miles) away in eastern Washington. In one fateful day, Mount. St. Helens had erupted about 1.3 km3 (46 billion cubic feet) of uncompacted ash - enough to fill Aloha Stadium in Honolulu about 90 times.
At Kilauea, the first and largest of the three recent explosive events occurred on March 19th. Obtaining an accurate measurement of the ash is challenging, due to the ability of the wind to remobilize the ash after it lands; preliminary estimates suggest that a tiny volume of less than 0.00001 km3 (350,000 cubic feet) of ash was erupted.
Since the March 19th event, the already modest ash deposition rates have steadily declined. During April, typical plume heights have been less than 1,500 m (5,000 ft), and the maximum ash thickness, measured directly adjacent to the vent, was around 3 cm (1 inch). A dusting of ash was reported on car windshields on Highway 11 near the National Park's Ka`u boundary, in Pahala, Wood Valley, and in Ocean View Estates, nearly 65 km (40 miles) to the southwest of Kilauea.
Kilauea's most recent explosion, which occurred very early Wednesday morning, produced a small amount of distinctive pink ash, composed mostly of rock dust. As of this writing, only one report of ash fall has been received from downwind communities.
At Kilauea, a little ash has created a lot of interest. The ash provides intriguing new opportunities for pursuing studies that are generally not possible in Hawai`i. In an eruption, as magma rises toward the surface and volcanic gases are released, gas-ash interactions occur, both within the vent, and potentially hundreds of kilometers (miles) downwind in the eruption plume. Gas and associated aerosols cling to the surface of the ash; by collecting the freshly deposited ash and soaking it in water or other liquids, the chemical coatings dissolve, and the solution can be analyzed.
Ash studies provide information on gas composition, the amount of gas released during an eruption, and potential environmental hazards. We are fortunate to have minor ash accumulation from Kilauea, for in eruptions with copious ash fall, there are numerous hazards, including damage to buildings, electronics, machinery, and power supplies. Health hazards include respiratory symptoms, eye irritation, and contamination of water supplies. Long-term hazards to livestock that grazes on ash-contaminated grass include fluorine poisoning. In addition, sulfur-rich ash may induce copper, cobalt, and selenium deficiencies. For a comprehensive discussion, see the Volcanic Ash Web page at volcanoes.usgs.gov/ash.
The recent appearance of ash at Kilauea has scientists from around the globe intrigued. Studies examining the fluorine, chlorine, sulfur, and trace metal content in the ash are underway. While contemporary watchers may find the current ash production a fresh chapter in Kilauea's history, observations over the past weeks have shown that wind and weather effects can easily obliterate the traces of explosive eruptions of this magnitude. Such eruptions may have occurred in the past with greater frequency than was previously suspected.
HVO continues to be interested in reports of ash accumulation in distant communities and pastures, and can be contacted by emailing firstname.lastname@example.org.
Kilauea summit and Pu`u `O`o continued to deflate. Sulfur dioxide emission rates and seismic tremor levels have remained elevated at several times background levels. Earthquakes were located primarily beneath Halema`uma`u Crater and the adjacent areas, the southwest rift zone, and the south flank faults.
Lava from the 2007 Thanksgiving Eve Breakout (TEB) flow, erupting from fissure D of the July 21 eruption, continues to flow through what remains of the Royal Gardens subdivision and across the coastal plain. On Wednesday, March 5, the flow entered the ocean (Waikupanaha entry) in the vicinity of Kapa`ahu. The Waikupanaha delta has since grown to a width of about 1,000 m (3,280 ft) and has multiple entry points. On March 15, another branch of the flow reached the ocean (Ki entry) farther to the east, within a few hundred meters of the lava viewing area. As of Thursday, April 17, both the Waikupanaha and Ki entries remained active.
The public should be aware that the ocean entry areas could collapse at any time, potentially generating large explosions in the process. The steam clouds rising from the entry areas are highly acidic and laced with glass particles. Do not venture onto the lava deltas. Even the intervening beaches are susceptible to large waves suddenly generated during delta collapse; these beaches should be avoided. Check the County of Hawai`i (http://www.lavainfo.us) for information on public access to the coastal plain and ocean entry.
For the first time in several weeks, several small surface flows have appeared on the rootless shield complex and on the lower flow field this week. One breakout, observed on April 16, sent a braided `a`a flow through the lower portions of Royal Gardens subdivision.
No incandescence was observed at night in Pu`u `O`o in the past week, though minor incandescence has been sporadically present throughout the past few months. As in years past, Pu`u `O`o likely is serving as a large chimney, beneath which lava is briefly stored and substantially degassed on its way to the eruption site.
On March 11, a new fumarole appeared low on the southeast wall of Halema`uma`u Crater, within Kilauea's summit caldera. The new vent is located directly beneath the Halema`uma`u Overlook about 70 m (230 ft) down. At 2:58 a.m., H.s.t., on March 19, a small explosion occurred from this fumarole. The explosion scattered rock debris over an area of about 75 acres, covering a narrow section of Crater Rim Drive, the entire Halema`uma`u parking area, and the trail leading to the overlook. The overlook was damaged by rocks that reached up to 90 cm (3 ft) across. No lava was erupted as part of the explosion, suggesting that the activity was driven by hydrothermal or gas sources. On April 9, another small explosion occurred, depositing dense blocks and particles of fresh lava on the overlook area. This week, another small explosion from the vent occurred at 3:57 a.m. on April 16, producing a dusting of pale-red ash west of the crater. The new explosion pit continues to vigorously vent gas and ash, with the plume alternating between brown (ash-rich) and white (ash-poor). Fresh lava spatter, Pele's tears and Pele's hair have been collected at the rim, indicating that magma resides at shallow depths in the new conduit.
Sulfur dioxide (SO2) emission rates from the summit area have been substantially elevated up to 10 times background values since early January; the emission rates for the past week have been decreasing but are still elevated. The increase in sulfur dioxide emission rates at the summit means that SO2 concentrations are much more likely to be at hazardous levels for visitor areas downwind of Halema`uma`u, especially during weak wind conditions or when winds blow from the south. Most people are sensitive to sulfur dioxide at these levels, especially children, individuals with asthma, chronic obstructive pulmonary disease (COPD), or other breathing problems. Stay informed about SO2 concentrations in continuously monitored areas (Jaggar Museum and Kilauea Visitor Center) by visiting the Kilauea Visitor Center and the web at:
Two earthquakes beneath Hawai`i Island were reported felt within the past week on the same day - Tuesday, April 15, or TAX DAY. A magnitude-2.9 earthquake occurred at 10:28 a.m., and was located 3 km (2 miles) east of Waimea at a depth of 12 km (8 mile). A magnitude-1.8 earthquake occurred at 10:49 a.m., and was located 7 km (4 miles) south of Volcano Village at a depth of 3 km (2 miles).
Mauna Loa is not erupting. Three earthquakes were located beneath the summit. The rate of extension between locations spanning the summit, indicating inflation, has decreased to values barely above current detection limits.
Visit our Web site (http://hvo.wr.usgs.gov) for daily Kilauea eruption updates and nearly real-time Hawai`i earthquake information. Kilauea daily update summaries are also available by phone at (808) 967-8862.
Updated: April 21, 2008 (pnf)