Pumice Ridges

A ridge of pumice was deposited at North Mission beach, Queensland, during the marine inundation generated by an intense tropical cyclone on March 10, 1918 (Taylor, 1982). The inundation occurred at high tide and was reported to have reached at least 3.5 m above normal sea level. The inundation resulted in the deaths of many people and transported and deposited onto the mainland supplies from a shed on Dunk Island approximately 5 km offshore. Indeed, one large bag of flour was deposited over 3.5 m high in a tree and the flour in the center of the bag was still sufficiently dry to be able to make damper (a type of bread) the following day after the maelstrom (Taylor, 1982). The crest of the pumice ridge here reaches 5 m AHD and it extends alongshore for approximately 500 m. This is the only reported ridge of pumice deposited during a tropical cyclone so far, and it is not known whether sand was also deposited along with pumice to form this ridge at the time. No sand occurs in the ridge today, for it is composed entirely of well-rounded pumice particles; however, a sand beach ridge (up to 3-4-m-high AHD) at South Mission Beach was reported (Taylor, 1982) to have been deposited during this same event. The source of the pumice is likely to be the volcanic islands to the east of Queensland such as Vanuatu although no detailed petrographic analyses have been undertaken to confirm this.

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