January 17, 2008
A weekly feature provided by scientists at the Hawaiian Volcano Observatory.
Royal Gardens is no stranger to lava flows
Royal Gardens subdivision was back in the news again this past week as a lava flow from the July 21 fissure advanced to within 300 m (985 ft) of the uppermost cross street. On the evening of January 8, a rootless shield near the fissure breached, releasing a flood of lava that formed a channelized `a`a flow. For the next five days, the flow advanced toward Royal Gardens until it stagnated late on January 13. As long as the rootless shields directly uphill of the subdivision remain active, this is likely to be a temporary reprieve for the two remaining residents.
Royal Gardens holds the dubious distinction of being the only inhabited area to be repeatedly invaded by lava flows throughout the 25-year span of the current eruption. It was the scene of the first house to be claimed by lava, back in March 1983, and it is also the site of the latest destruction--a long-abandoned house overrun in early 2007.
It's no surprise that Royal Gardens is a frequent destination for lava flows. The upper edge of the subdivision is only 5-6 km (3.1-3.7 mi) from Pu`u `O`o and Kupaianaha-the main vents of the past 25 years-and from the July 21 fissures.
Royal Gardens is not the only subdivision situated immediately adjacent to Kilauea's east rift zone. It holds the record, however, as the steepest subdivision on the volcano. Its streets run straight up Pulama pali, rising 1,400 vertical feet in just 3 km (2 mi).
Newcomers to the island might be surprised at the very existence of Royal Gardens. As with most of east Hawai`i's large subdivisions, Royal Gardens was the product of a speculative development spree that began in the late 1950s. Supported by both state and county officials, developers laid grids of substandard streets across vast tracts of land with no thought to sustainability, topography, or natural hazards. (This era in Big Island history rates its own chapter in Cooper and Daws' fascinating book, "Land and Power in Hawaii," published in 1985.)
Royal Gardens was heavily advertised on the mainland, and an estimated half to two-thirds of the lots were bought sight unseen. By the time the current eruption began, most of the 1,500 lots in Royal Gardens had been sold, but fewer than 75 houses were built.
That was fortunate, because from 1983-1985, `a`a flows fed by lava fountains from Pu`u `O`o overran the upper slopes of the subdivision during 7 eruptive episodes. Residents lived on edge in those years, when every 3-4 weeks towering lava fountains lit up the sky and rattled the windows. Sixteen houses were overrun, and 20 percent of the subdivision was inundated. Streets running straight down the pali formed convenient pathways for the `a`a flows, which filled them to a depth of 5-10 m (16-33 ft).
In July 1986, the eruption shifted 3 km (1.9 mi) downrift to the Kupaianaha vent. For the next five years, flows whittled away at the eastern side of Royal Gardens and wrapped around its lower end. By the end of 1991, less than 50 percent of the original subdivision was still exposed, and 39 houses had been destroyed.
Highway 130 was closed for good in early 1987, as tube-fed flows from Kupaianaha established a thoroughfare to the ocean. For the next 13 years, determined residents bulldozed a succession of short-lived access roads to Royal Gardens. The last such road was buried in 2000.
In early 1992, Kupaianaha died, and the eruption returned to flank vents on Pu`u `O`o cone. From 2000 to early 2007, flows approaching from the west encroached on the lower end of the subdivision, overlapping the Kupaianaha flows. During this time, 6 more houses were overrun.
Today, only about 35 percent of the original area of Royal Gardens is still uncovered by lava. The subdivision, once touted for its proximity to Hawai`i Volcanoes National Park "with all its spectacular attractions," is now one of the main attractions on helicopter tours of the eruption site. The remains of the development form an eerie kipuka of overgrown streets within the vast, barren lava field formed over the last quarter century.
Kilauea summit and Pu`u `O`o continued to deflate. Seismic tremor levels at the summit are elevated but are still at low levels. Summit sulfur dioxide emissions have nearly tripled. Earthquakes were located mostly beneath Halema`uma`u Crater and the south flank faults.
On July 21, 2007, lava began erupting from a set of fissures on the east flank of Pu'u 'O'o. Eruptive activity soon stabilized at fissure D, 2.3 kilometers (1.4 mi) northeast of Pu'u 'O'o. For most of last Fall, this lava was directed entirely into a perched lava channel, consisting of separate pools of molten lava separated by bridges of cooled lava. At dawn on November 21, lava began to erupt directly from fissure D, outside of the perched channel, creating the Thanksgiving Eve breakout (TEB) flow. Since December 27, the lava supply to the original perched channel has been completely redirected through the TEB outlet.
The TEB flow has continued to build itself vertically and laterally, as a series of low shields, over the last several weeks. Last week, the front of the southeast-most shield collapsed and a large volume of lava surged out to form a rapidly moving `a`a flow. The flow advanced about 3.4 km (2.1 miles) reaching to within 180 m (~590 ft) of the top of the Royal Gardens subdivision before stagnating over the weekend. As of Thursday, January 17, the eruption has resumed its construction of low shields and lava is confined to within about 2 km (1.2 miles) of the TEB outlet.
Weak incandescence in Pu'u 'O'o has been observed at night by Webcam a few times since early December, but has otherwise been absent since Aug. 31. As in years past, Pu'u 'O'o likely is serving as a large chimney, beneath which lava is stored briefly and degassed substantially enroute to the erupting fissure. Sloughing of Pu'u 'O'o into its own crater since late August has left numerous fresh cracks on the north rim and south flank of the cone.
Vent areas are hazardous. Access to the eruption site, in the Pu`u Kahauale`a Natural Area Reserve, is closed (http://www.state.hi.us/dlnr/chair/pio/HtmlNR/07-N076.htm).
No earthquakes beneath Hawai`i Island were reported felt within the past week.
Mauna Loa is not erupting. One earthquake was located beneath the summit. Extension between locations spanning the summit, indicating inflation, continues at steady, slow rates. The Mauna Loa webcam and gas sensors are again operational.
Visit our Web site (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: January 22, 2008 (pnf)