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In the case of the volcanic eruption of Mount Usu in 2000, there were no victims because the evacuation activities were carried out smoothly, as people made great use of the hazard map of Usu Volcano as a source of information. Also, the Mount Fuji Hazard Map Committee started work in 2001, scheduled to publicize the results in the near future. Although volcanic hazard maps have only recently captured the attention to people in Japan, they have been used in various overseas countries for many years. This paper summarizes the definition of volcanic hazard maps and the method of making volcanic hazard maps, classifies and analyzes the collected foreign cases, and introduces representative examples.

Synopsis:Water permeability of rust layers formed on a carbon steel and a low alloy steel by atmospheric corrosion was evaluated by means of impedance measurement of the rusted specimen electrode in 0.1 M sodium benzoate aqueus solution. Resistance of rust layer decreases with immersion time as the solution penetrates into the rust and finally attains a steady state. Initial and final values of the resistance and also the time necessary to reach the steady state increase with increasing of the periods of atmospheric exposure. These values are larger for low alloy steels than those for the carbon steel at the same exposure time. The linear relationship has been confirmed between atmospheric corrosion rates and reciprocals of the final resistances which provide a sort of measure for the porosity of rust layer. In case of low alloy steel the deviation of the final values from the linearity is found and the initial values come to agree with the line as exposure time becomes longer. It is supposed that corrosion rate depends on the time of wetness which determines how large is the area on the steel surface where the water reaches through the porosities and corrosion starts.

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SynopsisThe distribution oj elements in rust la)'eI" Jormed on IowaI/o)' steels (lfter several l)eriods oj exposures up to seven )'ears in industrial and rural atmospheres was investigated by means oj microscopic examination and electron probe microanalysis. The rust layer in large Pits contains coPI)er. I)hosphorus, and chromium with their locali:::ed distribution. Chromium and phosphorus concentrate around defects in th e rust such as voids and cracks. Th e local concentration oj col)l)er seems to diminish as the exposure I)eriod becomes longer. The rust la)ler nn tilefla t swface surrounding large I)its and also the surface layer above large I)its have shown no evidence qf localized concentration oj col)l)er and j)/lOsj)hol'lls and are characterized by the Jact that little chromium content is Jound in the rust. Silicon, main constituent qf dusts. has been Jound in these parts oj the rust, but none in the Pits. It is supposed that chromium. j)/lOsphorus. and copper transferred by corrosion reaction intn the solution I)resumably Jorm Jar less soluble compounds than Jerrous ion which diffuses out Jrom the pits and I)recipitates on outer surface.