火山灰年代法,^<210>Pbおよび^<137>Cs法による過去200年の榛名湖の堆積速度の推定

概要

論文の詳細を見る
A 90 cm sediment core (HAR 99A) from Lake Haruna, Gumma Prefecture, Japan was dated by tephrochronology, lead-210 and cesium-137 methods and was compared stratigraphically with the cores obtained in 1966 (HAR 96B) and 1971 (HAR 71). For the HAR 99A core, the 24-26 cm depth layer was estimated to be AD 1963 by ^<137>Cs. The tephra layer in 62-66 cm depth was identified to be volcanic ashes from Asama volcano eruption (Asama-A tephra: As-A) in AD 1783. Average mass sedimentation rate (AMSR) for 1963 to 1999 (0-26 cm depth) is 0.050 g cm^<-2>yr^<-1> and that for 1783 to 1963 (25-62 cm depth) is 0.033 g cm^<-2>yr^<-1>. AMSR for the 0-62 cm depth obtained by ^<210>Pb ranges between 0.052 and 0.058 g cm^<-2>yr^<-1>. In addition, it is proposed that the previous assignment of As-B (AD 1108) for a tephra layer at 40-50 cm depth of the HAR 71 core should be changed to As-A tephra (AD 1783).
2010-08-25