Debris flow probability and extent vary with infiltration rate and intensity-duration of rainfall: Mt. Mayon, Philippines
Jarod Maggio, Environmental Engineering
Advisor: Dr. Kurtis G. Paterson
Volcanoclastic debris flows or lahars triggered by intense rainfall due to bulking are influenced by surface characteristics that reduce the downward infiltration of groundwater after saturation. Variations in surface cover control storm water runoff, thus affecting the timing and volume of water entering a river channel prone to lahars. Rainfall induced debris flows constitute a serious geologic hazard to communities in many parts of the world. The abundant loose erodible material on volcanoes increases the likelihood and severity of large debris flow events; this combined with dense populations make volcanoes an important area for lahar research and mitigation measures. This study was carried out on the slopes of the Republic of the Philippines most active volcano, Mt. Mayon, in hopes of increasing the understanding of debris flow initiation. Two tipping bucket rain gauges equipped with data loggers were deployed to determine an intensity-duration rainfall threshold during quiescent periods on Mayon. The steady-state infiltration capacities of Mayons substrates were determined using a double-ring infiltrometer ponding method. Additional infiltrometer experiments were carried out with an overlying simulated ash layer of 10, 20, 30, 40, 50, and 100 mm in order to quantify the effects of tephra cover on ground infiltration, adding supporting data that decreased infiltration and increased likelihood of debris flow initiation occur after an eruptive event. Finally, sieve analyses of the volcanic substrates were conducted to better understand the variations of infiltration and runoff due to grain size distribution. An intensity-duration rainfall threshold for quiescent periods on Mayon was estimated to be (I=46.2D- 0.43). Average infiltration measurements ranged from 5.43-230.83 mm/hr depending on the type of substrate, vegetation cover, and grain size distribution. Simulated ash layers were found to increase initial infiltration (first 10 minutes) but decreased long-term infiltration (minutes - hours) between 2-30%. The average infiltration for each watershed was compared to the estimated volume of the lahars that were produced during Typhoon Reming in 2006, indicating a correlation between infiltration characteristics and debris flow severity.
Debris flow probability and extent vary with infiltration rate and intensity-duration of rainfall: Mt. Mayon, Philippines
Jarod Maggio, Environmental Engineering
Advisor: Dr. Kurtis G. Paterson
Volcanoclastic debris flows or lahars triggered by intense rainfall due to bulking are influenced by surface characteristics that reduce the downward infiltration of groundwater after saturation. Variations in surface cover control storm water runoff, thus affecting the timing and volume of water entering a river channel prone to lahars. Rainfall induced debris flows constitute a serious geologic hazard to communities in many parts of the world. The abundant loose erodible material on volcanoes increases the likelihood and severity of large debris flow events; this combined with dense populations make volcanoes an important area for lahar research and mitigation measures. This study was carried out on the slopes of the Republic of the Philippines most active volcano, Mt. Mayon, in hopes of increasing the understanding of debris flow initiation. Two tipping bucket rain gauges equipped with data loggers were deployed to determine an intensity-duration rainfall threshold during quiescent periods on Mayon. The steady-state infiltration capacities of Mayons substrates were determined using a double-ring infiltrometer ponding method. Additional infiltrometer experiments were carried out with an overlying simulated ash layer of 10, 20, 30, 40, 50, and 100 mm in order to quantify the effects of tephra cover on ground infiltration, adding supporting data that decreased infiltration and increased likelihood of debris flow initiation occur after an eruptive event. Finally, sieve analyses of the volcanic substrates were conducted to better understand the variations of infiltration and runoff due to grain size distribution. An intensity-duration rainfall threshold for quiescent periods on Mayon was estimated to be (I=46.2D- 0.43). Average infiltration measurements ranged from 5.43-230.83 mm/hr depending on the type of substrate, vegetation cover, and grain size distribution. Simulated ash layers were found to increase initial infiltration (first 10 minutes) but decreased long-term infiltration (minutes - hours) between 2-30%. The average infiltration for each watershed was compared to the estimated volume of the lahars that were produced during Typhoon Reming in 2006, indicating a correlation between infiltration characteristics and debris flow severity.