Volcanic rock is distributed extensively across Japan and is frequently subjected to hotwater property alteration. This paper has introduced the clay mineralization that occurs in these rocks as a result of the alteration process, together with associated engineering properties. The effects of montmorillonite on the rock material in which it has been generated has been examined in semi-quantitative analyses that are based on coloring tests. For residents of a volcanically active country where volcanic rock and volcanic bedrock are used extensively as construction materials including in structural foundations, it is extremely important to identify and resolve the engineering problems related to these rocks toward improving the durability of engineering structures and achieving economical site selection for such structures.
Ten percent of the world's active volcanoes are in Japan, where volcanoes can be seen from many cities and where people have historically lived near volcanoes. In most of Europe, in contrast, there is no volcanism, with the exception of a few countries such as Italy and Greece. In Japan, volcanoes have significantly affected people's habits, customs and views of nature. Regional development plans and civil engineering projects in Japan can only be carried out after the implementers gain a proper understanding of volcanoes and the materials they produce. Introduced here are the results of some studies on the use of volcanic rock as a construction material in Japan, especially regarding the engineering characteristics of such rock.
Volcanoes and earthquakes concentrate along the borders of tectonic plates, especially those borders encircling the Pacific Ocean.. Japan sits atop four tectonic plates: the Pacific, North American, Philippine and Eurasian plates. As the Pacific Plate moves west, it subducts the North American Plate. As the Philippine Plate moves north, it subducts the Eurasian Plate. The front of the subducting plate melts into magma deep underground before rising to ground level and gushing forth. The process has generated many active volcanoes in and around Japan, a country that accounts for approximately 10% of the world's active volcanoes (Fig. I). As a result, the strata and bedrock that form the basement rock in Japan typically have many faults and substantial depositions of effusive rock. In Japan, 26% of the ground surface is covered by volcanic deposits including volcanic rock. In addition to depositing lava and volcanic ash on the ground, volcanism causes hot water to rise surfaceward through faults and fissures, altering the properties of surrounding rocks. Rocks thus altered contain clay minerals that make them fragile. Unlike the fairly sound and continuous crustal blocks found in Europe, the bedrock in Japan has been divided into mosaic patterns by these tectonic processes (Fig.2). Also, in Japan high temperature and heavy precipitation lead to substantial accumulation of groundwater in bedrock, causing it to weather even at great ground depths. Therefore, bedrock of good quality can be found only at extremely great depths where weathering effects cannot reach. This makes it difficult to construct and maintain structures in these regions.