3:30 PM - 3:45 PM
[HTT14-01] Spatio-temporal analysis of displacement and precipitation of Unzen Fugendake lava dome using GBSAR and XRAIN
Keywords:lava dome, Unzen volcano, GBSAR, monitoring
INTRODUCTION
Lava dome collapses are critical hazards in volcanic regions, frequently occurring during eruptions. In certain cases, like Unzen-Fugendake on Shimabara Peninsula, significant parts of the dome persist post-eruption. The Heiseishinzan dome, formed during the 1991-1995 eruption, continues to slide yearly, posing ongoing risks. Past collapses at Unzen Fugendake(1991) are believed to be influenced by precipitation, yet precise measurements of rainfall on the dome are lacking, complicating the quantitative analysis of dome displacement and precipitation. This study aims to explore this relationship using high-resolution GBSAR data and direct precipitation measurements from XRAIN.
RESEARCH LOCATION
The focus is on Mt. Unzen Fugendake's lava dome in Nagasaki Prefecture, Japan. Born from the 1991-1995 eruptions, about 0.1 km³ of the dome still resides near the summit.
RESEARCH METHOD
In this study, a 19-block displacement dataset collected from Ground-Based Synthetic Aperture Radar (GBSAR) data with a 48-hour period was used to observe minute variations in the lava dome. For precipitation data, XRAIN (Xtended RAdar INformation Network) data from the MP radar network of MLIT and local precipitation data just above the Unzen lava dome are used. From the GBSAR and XRAIN datasets, we constructed (1) a displacement/precipitation dataset for each displacement event using the prominent displacement data and corresponding precipitation data in the GBSAR data, and (2) a dataset of spatial displacement changes of the lava dome during each event.
Result
(1) Response of lava dome to precipitation: The blocks of the lava dome show a significant rise or fall with increasing precipitation, especially in the dome front and dome 1-5 areas. (2) Displacement Events Not Related to Precipitation: Displacement events not directly related to precipitation or low precipitation were also observed. This may be due to natural moisture adjustment of the soil, groundwater movement, or a delayed response to precipitation that cannot be explained by the conventional lava dome collapse model. (3) Delayed response to precipitation: A lag in the response of lava domes to precipitation has been observed, ranging from immediate to 96 hours after precipitation. This delay in response suggests that the lava dome needs time to infiltrate precipitation.
DISCUSSION
(1) Precipitation and Dome Dynamics: While precipitation events correlate with dome displacements, they are not the sole cause. Rainfall-induced soil softening and erosion, affecting topography and internal structure, also play roles. Observations of low precipitation-related displacements suggest other causative factors. (2) Response Patterns and Time Lags: The observed time lag in dome responses to rainfall indicates a unique response pattern, contrasting with immediate reactions in previous studies of pyroclastic density flows. This necessitates revisiting past research. (3) Regional Displacement Patterns: The dome front and Dome 1-5 area showed significant rainfall responses, influenced by subsurface geological characteristics and internal structures. In the western block, soil stability and topography appear to affect displacement dynamics.
SUMMARY
This study elucidated the correlation between precipitation and Unzen lava dome dynamics. A rise or fall in the dome front and Dome 1-5 area was induced by increased precipitation. Concurrently, displacement events unrelated to precipitation were observed, potentially due to other factors like groundwater movement. Additionally, a notable time lag was observed in the dome's post-precipitation response, highlighting the complexity of environmental and geological interplays.
Lava dome collapses are critical hazards in volcanic regions, frequently occurring during eruptions. In certain cases, like Unzen-Fugendake on Shimabara Peninsula, significant parts of the dome persist post-eruption. The Heiseishinzan dome, formed during the 1991-1995 eruption, continues to slide yearly, posing ongoing risks. Past collapses at Unzen Fugendake(1991) are believed to be influenced by precipitation, yet precise measurements of rainfall on the dome are lacking, complicating the quantitative analysis of dome displacement and precipitation. This study aims to explore this relationship using high-resolution GBSAR data and direct precipitation measurements from XRAIN.
RESEARCH LOCATION
The focus is on Mt. Unzen Fugendake's lava dome in Nagasaki Prefecture, Japan. Born from the 1991-1995 eruptions, about 0.1 km³ of the dome still resides near the summit.
RESEARCH METHOD
In this study, a 19-block displacement dataset collected from Ground-Based Synthetic Aperture Radar (GBSAR) data with a 48-hour period was used to observe minute variations in the lava dome. For precipitation data, XRAIN (Xtended RAdar INformation Network) data from the MP radar network of MLIT and local precipitation data just above the Unzen lava dome are used. From the GBSAR and XRAIN datasets, we constructed (1) a displacement/precipitation dataset for each displacement event using the prominent displacement data and corresponding precipitation data in the GBSAR data, and (2) a dataset of spatial displacement changes of the lava dome during each event.
Result
(1) Response of lava dome to precipitation: The blocks of the lava dome show a significant rise or fall with increasing precipitation, especially in the dome front and dome 1-5 areas. (2) Displacement Events Not Related to Precipitation: Displacement events not directly related to precipitation or low precipitation were also observed. This may be due to natural moisture adjustment of the soil, groundwater movement, or a delayed response to precipitation that cannot be explained by the conventional lava dome collapse model. (3) Delayed response to precipitation: A lag in the response of lava domes to precipitation has been observed, ranging from immediate to 96 hours after precipitation. This delay in response suggests that the lava dome needs time to infiltrate precipitation.
DISCUSSION
(1) Precipitation and Dome Dynamics: While precipitation events correlate with dome displacements, they are not the sole cause. Rainfall-induced soil softening and erosion, affecting topography and internal structure, also play roles. Observations of low precipitation-related displacements suggest other causative factors. (2) Response Patterns and Time Lags: The observed time lag in dome responses to rainfall indicates a unique response pattern, contrasting with immediate reactions in previous studies of pyroclastic density flows. This necessitates revisiting past research. (3) Regional Displacement Patterns: The dome front and Dome 1-5 area showed significant rainfall responses, influenced by subsurface geological characteristics and internal structures. In the western block, soil stability and topography appear to affect displacement dynamics.
SUMMARY
This study elucidated the correlation between precipitation and Unzen lava dome dynamics. A rise or fall in the dome front and Dome 1-5 area was induced by increased precipitation. Concurrently, displacement events unrelated to precipitation were observed, potentially due to other factors like groundwater movement. Additionally, a notable time lag was observed in the dome's post-precipitation response, highlighting the complexity of environmental and geological interplays.