Mauna Loa (1907 Lava Flow)
With new technologies and innovative thinking about old technologies, scientists can reconstruct past geological events with a high amount of precision. The revisiting of past events is not only a testament to the technology of our modern age, but also aids geologists in understanding our Earth's history. For example, Dr. Zimbelman and others on the research team revisit the 1907 Mauna Loa basalt flow in Hawaii, bringing with them a modern tool, Differential Global Positioning system (DGPS), which obtains precision topography so they can evaluate the flow's extent. Their data reveals larger flow rates and lava area coverage than historically recorded. These data better quantifies the flow's extent, and will be useful in procuring potential hazard restrictions for future housing developments in the area around this active volcano.
Mauna Loa, a historically active volcano, can lay claim to being the world's largest volcano with its immense volume of 80,000 km3 1. The southwest rift zone (SWRZ) serves as the source region for three historic eruptions occurred in 1868, 1887, and 1907; the January 1907 lava flow is the westernmost of the three1. The volcano's recurrent eruptive nature has prompted various studies of the potential hazard of surface flows, resulting in the mapping of four high-level hazard zones. The 1907 flow is contained within hazard zones 1and 2, which are the zones where future eruptions are most likely to occur1.
A combination of newspaper articles, other historic published accounts, and eyewitness accounts provide context and constraints for the 1907 eruption. The eruption started the late evening of January 9, 1907 and lasted 15 days1. Within two days the lava flow hit a government road, and several days later another of the flow's lobes hit the road a few miles west of the first one1. The flow thicknesses ranged between 15 to 30 feet near the government road, and over 50 feet at the end of flow1. In 1946 Stearns and MacDonald estimated the total volume of lava flow volumes at 85 million m3, and Lipman increased this number to 110 million m3 in 19801.
The primary technique applied in this study center is precision topography, which is the qualitative documentation of elevation and slope of the volcanic landforms such as the lava flows. Adding to this method is the 3D positioning of the study area through the DGPS. In summary, these techniques are used to create profiles of various cross-sections, shown in Figure 1, through out the lava flow, and then statistical analysis is conducted to determine the area covered by the flow, volume, and the lava flow rates applying the new precise dimensions measured for the historic lava flow. Additionally, the results are compared with the historic accounts to justify accuracy. For example, the geologists know the rate they predict for the lava flow must correlate with the historical account asserting that the lava flow first crossed the government road on day two. Thus, they check to see if their calculated rate actually moves the lava the distance measured from the start of the eruption to the government road within a two-day period.
Channeled lava flows exhibit different morphology. During this study four morphological zones were established: stable, transitional, dispersed, and flow toe. The stable zone occurs early in the eruption consisting of a well-defined channel and levees that remain once established. Transitional flows contain a wider channeled portion and include some less-well-defined levees. If the 1907 flow were still active, the geologists could define the flow toe, which is where the flow is actively advancing down the hillside. Since the flow is inactive, only three zones were mapped out. See Figure 2 for the breakdown of the morphological zones of the 1907 flow.
In conclusion, the total area covered by flow is measured at 25.1 km2 and the total volume as 86.6 million3 1. Specifically, the eastern lobe covers an area of 13.1 km2, with a volume of 55.0 million m3, and had an effusion rate of 119 m3/s1. These findings indicate a strong likelihood of future eruptions along the southwest rift zone far beyond the area considered the rift zone proper1, thus cautioning the extent of future development near that area.
1. Dr. Zimbelman et al. (2008), Precision topography applied to an evaluation of the emplacement of the 1907 Mauna Loa basalt flow, Hawaii.