Chapter 6 - Deposits of the 1992 Nicaragua tsunami

Abstract

The 1992 Nicaragua tsunami left a sand sheet that is a few millimeters to about 10centimeters in thickness and also cobbles and boulders. Burrows beneath the deposit filled with coarse sediment record the passage of the steep front of the tsunami. Vertical grading is usually normal (fining upward) as is horizontal grading (inland fining). Detailed measurements of horizontal and vertical grading at Playa de Popoyo and nearby areas show local reversals of these grading trends. Horizontal grading of large clasts shows complex patterns, including patches and abrupt distal limits to transport. Two locations where vertical grading was measured along the same shore perpendicular line include specific distributions that can be correlated between locations. These locations show landward fining, resulting in one case from a thinning of the coarser basal section of the deposit and in another case from fining of the basal section. Overall, the simple, single wave of the 1992 Nicaragua tsunami, as recorded on tide gauges, was recorded sedimentologically as a fairly simple, single, normally graded bed.