Compressive phenomena of pyroclastic deposits and reliability of old documents

用1707年日本富士火山喷发和1783年日本浅间火山喷发的浮石和炉渣颗粒进行了单轴压缩实验。在干燥条件下，样品厚度的减少量随时间呈对数线性增加。单轴压缩条件下，Asama浮石的时间-位移对数线性曲线的斜率约为富士浮石的3.6倍。当颗粒大小相同时，无论颗粒的种类如何，骨料的最小表观密度与最大表观密度的比值都保持不变，为0.9。压缩实验表明，这些火山碎屑颗粒沉积在沉积后很短的时间间隔后达到最大值。然后，沉积200到300年后，表观密度基本保持不变。考察了前人收集和汇编的关于1707年富士火山渣土沉积的古老历史文献。与Aramaki等人的结果进行了比较。(1998)关于1783年阿萨马火山喷发，两者之间发现了一些显著的差异。在富士喷发的浮石中，可以观察到约1.69倍的夸大，而在1783个浅草浮石中，体积测厚的夸大倍数约为1.34倍，厚度的直接测量约为2.01倍。对1929年北海道-小松喷发和1770年和1814年樱岛火山喷发的浮石坠落沉积物进行了详细的工作。在这两种情况下，存款的保存情况都很差，收集的数据点不够好，以至于对数据的详细评估尚未完成。

Uniaxial compressive experiments were performed using pumice and scoria particles of the 1707 eruption of Fuji volcano and 1783 eruption of Asama volcano, Japan. Under dry condition, the decrease in thickness of the samples increases logalithmically linearly with time.The slope of the log-linear plottings, time versus displacement, of the Asama pumice, under uniaxial compression, is about 3.6 times greater that that of Fuji ejecta. When the particle size is uniform, the ratio of minimum to the maximum apparent density of the aggregates remains the same, at 0.9, irrespective of the kinds of particles.Compression experiments revealed that these pyroclastic particle deposits reaches a maximum value after a short time interval following deposition. Then, 200 to 300 years after the deposition, the apparent density stays more or less the same.Old historic documents were examined which were collected and compiled by the former researchers on the 1707 scoria fall deposit of Fuji volcano. When compared with the results by Aramaki et al. (1998) on the 1783 ejecta of Asama volcano, some significant discrepancies were found between the two. In Fuji ejecta, it is tentatively concluded that about 1.69 time of exaggeration is observable, while in the 1783 Asama pumice deposits, about 1.34 times of exaggeration for the volume-based thickness observation, and 2.01 time for the straight measurement of the thickness are observed.Filed work was made on the pumice fall deposits of the 1929 eruption of Hokkaido-Komagatake and the 1770 and 1814 eruption of Sakurajima volcano. In both cases, the preservation of the deposits are so poor, the collected data points are not good enough so that the detailed evaluation of the data are not yet completed.