April 5, 1996

A weekly feature provided by scientists at the Hawaiian Volcano Observatory.

Age and Appearance of Lava Flows

When visitors to this island arrive at the Keahole airport and travel along the Queen Ka'ahumanu highway to a hotel in south Kohala, they cannot help but notice the bare, black, glistening fields of lava. The flows, with their glassy surfaces, appear to have erupted yesterday.

The youngest flow along this coastline is 137 years old and is located on the north end of Kiholo Bay. The flows around Kona Village and the airport are nearly 200 years old. The rest of the flows are over 1,500 years in age. The low annual rainfall (10-20 inches) in the area accounts for the fresh appearance of the flow surfaces and the lack of vegetation.

The amount of rainfall determines the extent of weathering that occurs on the flow surfaces and the abundance of vegetation. In contrast to flows on the arid west side of the island, flows above Hilo from Mauna Loa are heavily vegetated and appear very old. Few people realize that the flow along Komohana Street between Mohouli and Puainako is only 115 years old. Kaumana Drive follows this same flow from Chong Street to above Kaumana City, and large 'ohi'a trees can be found throughout this flow. The annual rainfall of 100 to 200 inches contributes to the lush vegetation and severe weathering. The 1984 flows already have lichen, ferns, and small 'ohi'a growing on them.

Biologists have found Mauna Loa to be an ideal natural laboratory to study the effects of rainfall, temperature, and elevation on plant growth and decomposition. Geologists from the U.S. Geological Survey's Hawaiian Volcano Observatory have dated over 100 flows which provide the biologists with known time parameters. This allows them to compare plant communities and ecosystem functions on flows of similar ages on the wet and dry sides of the mountain.

The results of these studies will benefit geologists elsewhere when young lava flows may not be datable by any means except by the vegetation on the flows. Such studies as these are examples in which scientists of different disciplines collaborate in order to gain an increased understanding of their own area of expertise through the tools and techniques of other disciples for their mutual benefit.

Volcano Update

The current eruption of Kilauea continues unabated, with a large ocean entry near the Kamokuna bench and 4 smaller entries to the west. No explosive activity was observed. A major breakout from the tube system at the 550' elevation is feeding two flows. The eastern flow supplies the Kamokuna entry, and the western lobe is pooling in the Lae'apuki area. Visitors to the end of the Chain of Craters road are able to see the glow from these flows at night.

Three earthquakes were reported felt during the past week. A magnitude 3.1 located 8 miles northwest of Naalehu at a depth of 1 mile, occurred at 2:48 a.m. on March 31. It was reported felt in Hawaiian Ocean View Estates subdivision. The second earthquake occurred on April 1 at 9:58 a.m. and was felt in Paauilo and Laupahoehoe. The epicenter of this magnitude 2.7 earthquake was 4 miles southeast of Paauilo at a depth of 10 miles. Residents of north Kona reported feeling an earthquake at 10:27 p.m. on April 4. It was located 1 mile northeast of Holualoa at a depth of 13 miles and had a magnitude of 3.2. No damage was reported as a result of the earthquakes.