Recent Rhodolith Deposits Stranded on the Windward Shores of Maio (Cape Verde Islands): Historical Resource for the Local Economy

Markes E. Johnson*, B. Gudveig Baarli, Carlos M. Da Silva, Mário Cachão, Ricardo S. Ramalho, Ana Santos, Eduardo J. Mayoral

*Corresponding author for this work

Research output: Contribution to journalArticle (Academic Journal)peer-review

4 Citations (Scopus)

Abstract

Maio is a volcanic island with an area of 269 km2 in the Cape Verde archipelago off the west coast of Africa. Although considered a leeward island, it absorbs NE trade winds that typically register 5 to 6 on the Beaufort Scale (moderate to fresh breeze). The trade winds produce ocean swells commonly 3.5 m in height that scour the island's north coast but also generate eastern longshore currents. Outcrops with Pleistocene rhodoliths occur on the SE and south shores and include lithified dunes mainly composed of crushed rhodolith debris. In contrast, the modern beaches and Pleistocene dunes on the more sheltered west coast are practically devoid of rhodoliths. Present-day rhodolith banks off the north coast would seem to be precluded by intense wave action. This study examines rhodoliths from overwash and beach-rock deposits around Ponta Cais in the far north. Lumpy rhodoliths (likely Lithothamnion sp.) are concentrated in a sheltered corner on the bay south of Ponta Branca. A more extensive overwash deposit covers an area of 27,000 m2 that is 1 m above mean sea level with a surface exposure of 450 rhodoliths/m2. A unique specimen nucleated around a ceramic fragment indicates that the deposit is historical in context. Rhodolith beach rock extends all along Praia Real east of Ponta Cais. A northern bank clearly exists, but it does so at a water depth normally adequate to protect larger rhodoliths from all but major storms. Abandoned limekilns behind Praia Real demonstrate that the local economy on a volcanic island used rhodoliths as a source of mortar and whitewash.

Original languageEnglish
Pages (from-to)735-743
Number of pages9
JournalJournal of Coastal Research
Volume32
Issue number4
DOIs
Publication statusPublished - 1 Jul 2016

Keywords

  • Beach rock
  • calcium-carbonate resources
  • limekilns
  • NE trade winds
  • supratidal deposits
  • volcanic islands

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