大屯火山群火山噴氣孔噴泥事件初探

Abstract

自2021年底起，大屯火山群出現多起具代表性的火山噴泥事件，顯示其後火山活動型態可能已由單純的氣體逸散或泉水湧出，轉變為涉及封蓋層破裂與熱液壓力釋放的新機制。為探討此類事件的成因與地下熱液系統的動態變化，本研究針對大油坑、小油坑與焿子坪三處活動區域所採集的11筆火山泥樣本，進行X光繞射 (XRD) 與掃描式電子顯微鏡-能譜分析 (SEM-EDS)，並結合水化學監測資料加以解析。研究結果顯示樣本中廣泛存在Cristobalite、Quartz、Pyrite、Alunite與少量Illite、Kaolinite等礦物，反映其形成於100 - 250 °C、pH ＜ 3之酸性蒸氣交代環境。SEM-EDS影像揭示多階段交代與氣液混合沉澱的顆粒特徵。水化學監測亦顯示噴泥事件前常伴隨Cl-、SO42-、Total dissolved solids (TDS) 等離子濃度短期異常上升，對應流體通道變化與封蓋層壓力釋放之可能徵兆。綜合礦物與水化學證據指出，噴泥樣本具多來源特性，可能為不同深度熱液物質的混合所致，且與箱根火山2015年蒸氣噴發事件的礦物組成高度相似，支持其屬於小規模蒸氣噴發的推論。本研究建立了礦物學與水化學交叉驗證之分析框架，證實結合XRD、SEM-EDS與監測資料可有效提升對後火山活動之理解，並對未來火山監測與蒸氣噴發預警機制提供關鍵參考。

Since late 2021, a series of mud discharge events have occurred at the Tatun Volcano Group (TVG), suggesting a transition in post-volcanic activity from typical gas emission and spring flow to mechanisms involving caprock rupture and hydro-thermal overpressure release. To investigate the origin and subsurface processes of these events, this study analyzes 11 mud samples collected from three major fumarolic areas Dayoukeng (DYK), Xiaoyoukeng (SYK), and Gentzuping (GTP) using X-ray diffraction (XRD) and scanning electron microscopy with energy-dispersive spec-troscopy (SEM-EDS), complemented by hydrochemical monitoring data.XRD results reveal the widespread presence of cristobalite, quartz, pyrite, alunite, and minor amounts of illite and kaolinite, indicative of mineral formation under highly acidic (pH< 3) vapor-phase alteration conditions at temperatures of 100 – 250°C. SEM-EDS imagery shows multi-stage mineral deposition and gas-liquid interaction textures. Hydrochemical time series from DYK and GTP demonstrate transient spikes in Cl-, SO42-, and TDS prior to several mud events, suggesting pressure accumulation and seal failure in shallow hydrothermal zones. The mineral assemblages exhibit char-acteristics of mixed-depth origins and closely resemble those observed in the 2015 steam eruptionproducts at Hakone Volcano, Japan, supporting the interpretation that these events represent small-scale phreatic eruptions.This study establishes a robust cross-validation framework integrating mineralog-ical and hydrochemical indicators. The findings highlight the potential of combining water chemistry monitoring with mineral phase analysis to improve the detection and interpretation of phreatic eruption precursors, offering valuable insights for future volcanic hazard assessment.