Volcaniclastic tide-modulated tempestite in a coastal tuff ring, Jeju Island, Korea

Chanwoo Sohn,Young Kwan Sohn

doi:10.1038/s41598-019-39784-0

Abstract

The need for more accurate and extensive records of storm activity is increasing because of growing population and infrastructure in coastal areas. Records of past storm activity have consequently been sought from diverse sedimentary proxies in marginal marine environments, as well as historical documents. In this paper, we introduce a unique record of a 3.7 ka BP storm event preserved in a coastal tuff ring on Jeju Island, Korea. The tuff ring formed mostly above high tide level by primary volcanic processes, but contains three interbeds of horizontally laminated to hummocky/swaly cross-stratified deposits with intervening mud drapes up to an altitude of ~4.6 m above high tide level. These interbeds were formed by wave activity in a swash to surf zone when the sea level rose several meters above normal high-tide level during a storm event, and the triple intercalation of the wave-worked deposits reflects three tidal cycles during a storm event that lasted 1.5 day. Jeju Island contains the most complete record of an ancient storm event ever reported in the tuff ring, and highlights the significance of coastal volcanoes in the study of extreme depositional events in coastal areas, such as storms and tsunamis.

Highlights

Volcaniclastic deposits can preserve high-resolution records of earth surface processes, such as daily to millennial-scale sea-level fluctuations[1,2] and fair-weather marine processes[3], even in coastal areas vulnerable to erosion because they accumulate commonly with extremely high sedimentation rate
The Songaksan tuff ring accumulated mostly above high tide level by pyroclastic surges and airfall except for the basal one meter-thick section, which was deposited in an intertidal setting and contains wave-worked deposits[2]
Unit R1, characterized by the absence of swash zone facies and the localized reworking only at locality 10 (Fig. 3A), suggests inundation of the tuff ring up to an altitude of ~5.5 m followed by suspension settling of fines without significant wave activity throughout the first tidal cycle of the storm event

Summary

Site Characteristics

Jeju Island is an alkali basaltic volcano built in a tectonically stable intraplate setting in the southeastern Yellow Sea[5] (Fig. 1A). Songaksan is the youngest volcanic center on the island, which erupted ~3.7 ka BP1,6 and consists of a basaltic tuff ring, a nested scoria cone and a ponded lava inside the crater[1] (Fig. 1B). The sea level at that time was almost identical to that at present. (All altitude data were obtained by the South S82T RTK GPS surveying unit and are expressed in terms of mean sea level.) Vertical crustal motion is regarded to have been negligible in the Jeju Island area because the area is located in an intraplate setting that is tectonically more stable than other regions in East Asia[7]. Most typhoon routes are adjacent to Jeju Island (Fig. 1A)

Deposit Characteristics

Methods

Additional Information