Submerged karst landforms observed by multibeam bathymetric survey in Nagura Bay, Ishigaki Island, southwestern Japan

Hironobu Kan, Kensaku Urata, Masayuki Nagao, Nobuyuki Hori, Kazuhiko Fujita, Yusuke Yokoyama, Yosuke Nakashima, Tomoya Ohashi, Kazuhisa Goto, Atsushi Suzuki

    Research output: Contribution to journalArticlepeer-review

    13 Citations (Scopus)

    Abstract

    Submerged tropical karst features were discovered in Nagura Bay on Ishigaki Island in the southern Ryukyu Islands, Japan. The coastal seafloor at depths shallower than ~. 130. m has been subjected to repeated and alternating subaerial erosion and sedimentation during periods of Quaternary sea-level lowstands. We conducted a broadband multibeam survey in the central area of Nagura Bay (1.85. ×. 2.7. km) and visualized the high-resolution bathymetric results over a depth range of 1.6-58.5. m. Various types of humid tropical karst landforms were found to coexist within the bay, including fluviokarst, doline karst, cockpit karst, polygonal karst, uvalas, and mega-dolines. Although these submerged karst landforms are covered by thick postglacial reef and reef sediments, their shapes and sizes are distinct from those associated with coral reef geomorphology. The submerged landscape of Nagura Bay likely formed during multiple glacial and interglacial periods. According to our bathymetric results and the aerial photographs of the coastal area, this submerged karst landscape appears to have developed throughout Nagura Bay (i.e., over an area of approximately 6. ×. 5. km) and represents the largest submerged karst in Japan.

    Original languageEnglish
    Pages (from-to)112-124
    Number of pages13
    JournalGeomorphology
    Volume229
    DOIs
    Publication statusPublished - 2015 Jan 5

    Keywords

    • Coral reef
    • Japan
    • Multibeam echosounder
    • Ryukyu Islands
    • SCUBA
    • Submerged karst

    ASJC Scopus subject areas

    • Earth-Surface Processes

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