Volcano Watch — Fishponds versus lava flows

The North Kona Coast of the Big Island is fortunate to have several Hawaiian fishponds preserved. These ponds were major construction feats by which Hawaiians cultivated fish. Good examples are `Aimakapa and Kaloko in the Kaloko-Honokohau National Park, Ku`uali`i and Kahapapa in front of the Royal Waikoloan Hotel, and several others on the grounds of the Orchid at Mauna Lani. It is not generally known that there were two larger fishponds in the same Kona coast area that were refurbished and maintained by Kamehameha before each of them was destroyed by lava flows.

The largest fishpond was probably Pa`aiea located between Keahole Point (actually Ho`ona) and Mahai`ula (actually Kaelehuluhulu). It was said to have been three miles long and about one-half mile wide and consisted of relatively shallow water with many small islets within the pond. Some say that it was a loko pu`u one, or a fishpond bounded by a natural sand berm. The fishpond Pa`aiea was completely covered by the Hu`ehu`e flow from Hualālai in 1801. There are no pieces left untouched. Recent mapping of stranded beach and ocean entry deposits within the Hu`ehu`e flow shows that this flow extended the coastline out at least one mile and added nearly four square kilometers (nearly 1000 acres) to the island.

The first phase of the eruption moved fairly rapidly and built several large pahoehoe channels and tubes to transport the lava from the vent to the ocean. The last phase was much slower and was very much like pahoehoe formed by the current eruption of Kīlauea. The pahoehoe of the last phase also moved through a tube. Kamehameha is said to have offered a lock of his hair to stop the eruption from destroying more property.

After the destruction of Kamehameha's favorite fishpond, Pa`aiea, he ordered another fishpond to be rebuilt as a replacement. That pond was named Wainanali`i and was located on the north side of Kiholo Bay. Laborers from at least three districts worked several tens of thousands of hours to complete this effort by about 1812. Wainanali`i was said to have been a deep-water pond capable of keeping ahi and aku within stone walls said to be not less than two mile in circumference. As with Pa`aiea, this pond was destroyed by lava from Mauna Loa in 1859. Only a portion of one wall is said to remain along with pieces of a shore platform.

This particular eruption of Mauna Loa also occurred in two phases—the first was a very rapid `a`a flow that traveled 50 km (31 miles) in 8 days. The last phase was a much slower pahoehoe flow that fed lava into the ocean for approximately five months.

The number of lava flows reaching this part of the coast was unprecendented in the 19th century (1800s). Two flows in the same century destroyed two fishponds. Based on an average recurrence of four flows in the last 1,000 years that have reached that coast, there is a 33% chance of one flow per century and only a 5% chance of two flows per century! It is unfortunate that those two flows scored direct hits on large public works projects like these fishponds. The siting of fishponds in natural bays probably meant that they might be more susceptible to destruction by a lava flow.

Even though each of these fishponds supported moderate populations in the 19th century, the population along the North Kona Coast may now be more dense. As devastating as the loss of these fishponds was then, it would be much more devastating to lose a large resort or housing development now.

Volcano Activity Update

Kīlauea's east rift zone eruptive activity continued unabated during the past week. On July 21, lava topped the east and west rims of the Pu`u `O`o crater and flowed down the sides of the cone for a few minutes before the pond level subsided. Lava continues to flow through a tube system to the ocean. The ocean entry is in the Kamokuna area west of Waha`ula. The public is reminded that the area is extremely hazardous with frequent collapses of the lava delta accompanied by explosions.

There were no earthquakes reported felt during the past week.