Volcano Watch - What if the 1984 flow from Mauna Loa hadn't stopped?

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Several recent "Volcano Watch" columns have dealt with Mauna Loa and the implications of renewed inflation of its summit. For better or worse, this one will be no different except that it will be a "What if," rather than a "What is," topic. What if the lava flow produced in the most recent eruption of Mauna Loa had continued to Hilo? Where would the flow have gone?

At the time, many thought that the flow was heading for Waiakea Uka, but it was actually on a path that would have taken it into the upper Kaumana area. How do we know this? Lava, like water, flows downhill, so that we can use a digital elevation model of the Big Island to calculate fairly precise downhill paths. Of course, our computed paths are only as good as the digital elevation model, which is just a computer version of the familiar USGS contour maps.

One check on the accuracy of these computed paths is to compare them with the actual path of the 1984 flow. A quick computation shows that the computed path was pretty good and would have successfully predicted 65 percent of the actual flow path. The maximum difference between the computed and actual path was 750 meters (2,500 feet). The lowest third of the flow was predicted with nearly 100 percent accuracy.

In 1984, the lava flow stopped 8.5 km (5.3 miles) short of Country Club Road off Kaumana Drive. If the flow had continued, it would have touched the south end of Country Club Road and continued across Wilder Avenue at about the intersection with the new Pu'ainako extension. Depending on how wide the flow was, it might have already blocked Kaumana Drive. From there, the flow would have progressed along Mele Manu Street, and through the south side of the upper section of the Sunrise Estates subdivision, thence down the Mohouli extension to its intersection with Komohana Avenue.

Not waiting for the light to change, the 1984 flow would have crossed Komohana and taken a course that was slightly toward Hamakua from Mohouli Street, advancing along Ho'opuni Way, Hale Nani, and Hualalai Street before finally entering the ocean somewhere between Pauahi Street and the Mo'oheau Bandstand.

While we're imagining this fictitious flow going through Hilo, let's think about its effects. The obvious ones are that Hilo would be split, with no vehicular access across the flow, roughly at Mohouli and Hualalai Streets. If Kaumana was also blocked above 'Akolea Road, then the only escape from north Hilo would be towards Hamakua. Citizens living above Country Club Road would be cut off from either part of Hilo. These barriers to travel would also complicate fighting the inevitable fires that would be set along the flow's path.

A flow entering Hilo Bay would pose additional threats. First, the ocean-lava interaction would produce a steam cloud laden with acid droplets and glass particles that would largely be blown back onto the flow and surrounding areas during normal trade winds. This would not disrupt air travel into and out of Hilo airport unless winds shifted or the entry location changed. The second major effect would be that the flow could quickly build a delta inside the shallow Hilo Bay that would extend out to the breakwater and effectively close off our commercial port.

How likely is it that a lava flow will really reach Hilo Bay? Not likely. Of the six Mauna Loa flows that came toward Hilo in the last 150 years, only one crossed what is now Komohana Street. The 1881 lava flow stopped 2 km (1.2 miles) short of entering Hilo Bay. Based on mapping and the examination of older deposits encountered in a deep research drill hole near the airport, Mauna Loa flows have neared the bay on average every 3,500 to 5,000 years. The last time was 1,200 years ago, when the Pana'ewa flow, which underlies the airport and most of Keaukaha, was emplaced.

Volcano Activity Update

Eruptive activity of Kilauea Volcano continued unabated at the Puu Oo vent during the past week. A narrow flow worked its way along the eastern margin of the Mother's Day flow from Paliuli to the coast. The flow stagnated shortly after entering the ocean east of Highcastle. Lava continues to enter the ocean from the Wilipea and West Highcastle lava deltas. The public is reminded that the ocean entry areas are extremely hazardous, with explosions accompanying sudden collapses of the new land. The steam clouds are highly acidic and laced with glass particles. The National Park Service has erected a rope barricade to delineate the edge of the restricted area. Do not venture beyond this rope boundary and onto the lava deltas and benches.

One earthquake was reported felt in the week ending on October 31. Residents of Waimea and Pa`auilo felt an earthquake at 7:38 a.m. on October 30. The magnitude-2.2 earthquake was located 4 km (2.4 mi) east of Waimea at a depth of 18.9 km (11.3 mi).

Mauna Loa is not erupting. The summit region continues to inflate. The earthquake activity is low with only 8 earthquakes located in the summit area during the last seven days.