EFFECTS OF THE LUNAR CYCLE AND CHANGING BAROMETRIC PRESSURE ON THE TIMING AND INTENSITY OF ERUPTIONS AT OL DOINYO LENGAI VOLCANO, TANZANIA

In an effort to gain more understanding of the processes that trigger the onset of volcanic activity, volcanologists are interested in possible influences of external factors such as seasonal changes, the lunar cycle, and weather conditions. To date, most research of this type consists of correlating historical eruptions to seasonal and weather patterns over periods of many years, or gathering similar data during relatively short observation periods at certain volcanoes. In 2004, similar research was conducted at Ol Doinyo Lengai volcano, African Rift Valley, northern Tanzania, by recording eruption data and examining relationships to the corresponding lunar cycle and barometric pressure. Ol Doinyo Lengai was chosen for study because it erupts natrocarbonatite lava, which has the lowest temperature and viscosity of all lavas. The volcano has been in a near-continuous state of eruption since 1983. It is hypothesized that due to the extremely low viscosity of natrocarbonatite magma, tidal and weather influences may be more easily detected at Ol Doinyo Lengai than at volcanoes erupting higher viscosity lavas. From 29 June to 29 July, 2004, a continuous presence was maintained in the summit craters of Ol Doinyo Lengai. Continuous barometric pressure readings were recorded using a NovaLynx Model 230-7020-A barograph. An hourly record of eruption location and intensity was recorded using a numerical scale designed to rate the strength of eruptions. Assessment of eruption strength was based on seven weeks of prior observations in the crater during eight visits between 1997 and 2003. Data are analyzed using theoretical earth tides calculated by TSOFT software, developed by the Royal Observatory of Belgium. Spectral analysis indicates no correlation between eruption frequency and barometric pressure or the diurnal tidal cycle. However, time series analysis of activity data indicates a low frequency component with a period of approximately 8.5 days. The two most intense eruptive episodes occurred within two days of the new and full moon, respectively. The observation period was not long enough to determine if these low frequency components are statistically significant. A second long-term stay during summer 2005 will include observations during new and full moon phases, each of which will nearly coincide with a lunar apogee or perigee.