A dynamical study of marine terrace formation

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(1) In order to examine what kind of landforms is created when waves are allowed to act on a gently sloping rock surface emerged as a result of uplift of the land, a laboratory test was performed using a model rocky coast with a uniform slope of 1/10. The model was made using a mixture of cement, sand, and water. The result showed that an abrasion terrace with a similar gradient to the original slope was formed in the surf zone and the shoreline angle was located slightly higher above Still Water Level.(2) A mathematical model was constructed to describe the formation of Holocence marine rockterraces. The terrace width, W , is expressed byWi= [ Zi (B + Ri <tau>i + <lambda>i )/ h_b ] -R_<i+1> <tau>_<i+1> ( i = 1,2,・・・n) where Z is the amount of sea level fall, R is the recession rate of coastal cliffs, <tau> is the time for sea level stillstand, R<tau> is the recession distance of the cliffs, <lambda> is the horizontal distance from the intersecting point of sea level and the original landform profile to the initial coastline position, B is the width of abrasion terrace on the original landform, h_b is the maximum water depth for submarine abrasion, and the suffixes i-l, i, and i+l denote the sea levels i-l, i, and i+l, respectively.(3) Seven coastal terraces well develop near Pukemuri Stream, Wairarapa, New Zealad, where the ages of three terraces (II, III, and IV ) out of seven are unknown. The above model was applied to this site to estimate the ages of these terraces. The result showed that the ages of II-, III-, and IV-terraces were estimated at 6,000, 5,300, and 4,300 y B.P., respectively.In this estimation, the age values for V-and VI-terraces were used for reference values. The estimated I-terrace age was 7,000 y B.P.which is colse to ^<14>C-value of I-terrace,about 6,700 y B.P. This suggests that model is reasonable.