The increase in the number of earthquakes and in the temperature of the hot springs that occurred between 1995 and 1997 on the islands of Saba and St. Eustatius, located in the Northern Lesser Antilles, was more than a mere fluke in subterranean activity: a mild volcano-seismic crisis had produced an increased heat flow. This book investigates this correlation and other geologic activity of the active volcanoes in the Northern Lesser Antilles. A well-researched document of the volcanoes on these two highly populated islands, the book also features five detailed maps of the region and is an ideal accompaniment to the Netherlands Geological Survey’s geohazard report, which recommends the initiation of routine monitoring of both islands.
I . , II III Volcanology of Saba and St. Eustatius, Northern Lesser Antilles M. John Roobol and Alan L. Smith , , IV Digital versions of the maps in this volume and other supporting materials are presented on the website of the Royal Netherlands Academy of Arts and Sciences, see www.knaw.nl/edita/antilles Royal Netherlands Academy of Arts and Sciences P.O. Box , GC Amsterdam, the Netherlands T + - - F + - - E
[email protected] www.knaw.nl - - - The paper in this publication meets the requirements of « iso-norm ( ) for permanence © Royal Netherlands Academy of Arts and Sciences No part of this publication may be reproduced, stored in a retrieval system or transmitted in any form or by any means, electronic, mechanical, photocopying, recording or otherwise, without the prior written permission of the publisher. V Contents List of Plates Abstract Acknowledgments XI XII XVIII Island Arcs of the eastern Caribbean The composite arc of the Lesser Antilles 3 The Active Arc 3 The Extinct Arc of the Limestone Caribbees 5 The Aves Ridge 6 Venezuela and Grenada basins Submarine banks of the northern Lesser Antilles Anegada Passage 8 Kallinago Depression 9 Seismically active faults 9 Faults revealed by seismic reflection profiles 10 Lineaments 11 Drilling and seismic reflection studies on the Saba Bank 11 Mesozoic rocks of St. Croix and La Desirade islands 13 Mesozoic rocks dredged from submarine scarps on banks in the northeastern Caribbean 13 Discussion 14 1 2 7 7 VI Contents Introduction Development of pyroclastic studies in the Lesser Antilles Classification of pyroclastic deposits of the Lesser Antilles Pelean-style eruptions 23 St. Vincent-style eruptions 25 Plinian-style eruptions 25 Asama-style eruptions 26 Phreatic- / phreatomagmatic-style eruptions 27 Volcaniclastic deposits lacking primary pyroclastic structures 28 Introduction Morphology and bathymmetry of Saba Geology of Saba The horseshoe-shaped crater / sector collapse structure of Saba 35 The older volcanic division of Saba 40 The younger volcanic division of Saba 43 Geochronology of Saba Pyroclastic stratigraphy of Saba Grain size characteristics 48 The most recent eruption of Saba Structural evolution of Saba 17 17 20 22 31 31 31 34 44 47 51 57 59 Introduction 59 Petrography of the volcanic rocks and their inclusions 61 Basalt 62 Basaltic andesite 62 Andesite 65 Dacite 65 Partially resorbed bipyramidal quartz in the volcanic rocks of Saba 65