July 8, 2004
A weekly feature provided by scientists at the Hawaiian Volcano Observatory.
Hualalai Volcano: Kailua-Kona's intriguing neighbor
Visitors and residents of the Big Island's "gold" or Kona coast enjoy beautiful beaches, great snorkeling and lovely sunsets. Early risers may also get a good view of the summit of Hualalai volcano before the inversion-layer clouds come and blanket the peak.
Located only 10 miles (15 km) from the coastal areas of the town of Kailua-Kona, the summit of Hualalai rises to 8,271 ft (2,521 m). Although its quiet presence has become a familiar site, the intriguing landscape and potential impact of the volcano may be under-appreciated. Hualalai places an undistinguished third in a number of comparisons of the five Big Island volcanoes. It is the third tallest, third oldest, and third most active volcano on the island. It is even the runner up in the category of smallest volcano, in area above sea-level. Kohala wins that title, making up only about 6 percent of the island, while Hualalai runs a close second at around 7 percent. Huge Mauna Loa makes up 51 percent, Mauna Kea nearly 25 percent, and Kilauea 14 percent of the Big Island.
One interesting trait is that Hualalai has three rift zones, one more than its active volcanic relatives, Mauna Loa and Kilauea. One of these rift zones (an area of weakness extending down the flank of a volcano) was the site of the most recent eruptions. Very fluid, fast-moving flows from the northwest rift zone erupted for undefined periods before 1801. The largest and best known of these flows are the Ka`upulehu flow -- which erupted from the 5,500 to 6,000-ft elevation and entered the ocean between the Kona Village Resort and Kiholo Bay -- and the Hu`ehu`e flow, upon which most of the Keahole airport is built. The Hu`ehu`e flow erupted from around the 500-ft elevation and destroyed Kamehameha's large and valuable fish pond Pa`aiea, located between Keahole Point and Mahai`ula. An estimated 50 million cubic meters of lava was produced during this eruption, an amount generated by five to six months of the current Kilauea eruption.
Looking up at Hualalai, one observes a steeper and "bumpier" profile than the smooth, gradual shield-volcano profile of Mauna Loa. Hualalai is in the "post-shield stage" of its life cycle and is moving off the hotspot that feeds Hawaiian eruptions. During this stage, the rate of eruptions is reduced, and much more erosion and weathering of the volcano can occur between eruptions.
Although the temperatures of most recent flows from Hualalai were 1150-1220 ?C (2100-2230 ?F), at least as hot as Kilauea's lava temperatures, volcanoes in the post-shield stage tend to erupt lava that is slightly cooler, stickier, and gas-rich than during the earlier shield-building stage. This results in thick flows that steepen the sides of the volcano. It also causes explosive eruptions and high fountains that form cinder cones along its profile. The combination of cinder cones and thicker, more viscous flows concentrated near the summit causes Hawaiian volcanoes in this post-shield stage to be noticeably steeper and bumpier than in earlier shield-building stages. Although volcanoes in the post-shield stage tend not to have a single summit caldera, multiple cones and craters dot the summit area of Hualalai.
Hualalai erupts every few hundred years. In 1929, a series of several thousand earthquakes came from beneath Hualalai's northern flank, shaking the island of Hawai`i. Some of the earthquakes were strong enough to do damage in central Kona and were felt as far away as Honolulu. They were likely associated with subsurface movements of magma or readjustment of the mountain as a result of such movement.
At some future date, Hualalai will erupt again, and favorite picturesque beaches of Kona could be replaced by sections of lava-covered coastline. Hualalai should not be taken for granted. We should enjoy the beauty of the mountain and its downslope areas while we can.
Eruptive activity at Pu`u `O`o continues. The Banana flow, which breaks out of the Mother's Day lava tube a short distance above Pulama pali, is entering the ocean off the 2002 Wilipe`a lava delta. The national park has marked a trail to within a short distance of the active lava delta, and thousands have been enjoying the show. In addition, lava has been visible between Pulama pali and Paliuli for the past several weeks, and on occasion lava cascades down Paliuli to the coastal flat. Eruptive activity in Pu`u `O`o's crater is weak, with sporadic minor spattering and small flows.
No earthquakes were reported felt on the island during the week ending July 7.
Mauna Loa is not erupting. The summit region continues to inflate slowly. Seismic activity remains low, with 6 earthquakes located in the summit area during the past week.
Updated: July 15, 2004 (pnf)