Later stages of volcanic evolution of La Palma, Canary Islands: Rift evolution, giant landslides, and the genesis of the Caldera de Taburiente Juan Carlos Carracedo* Estación Volcanológica de Canarias, IPNA-CSIC, P.O. Box 195, 38206, La Laguna, Tenerife, Spain, and Department of Geography and Geology, Cheltenham and Gloucester College of Higher Education, United Kingdom Simon J. Day Department of Geography and Geology, Cheltenham and Gloucester College of Higher Education, United Kingdom, and Greig Fester Centre for Hazards Research, University College London, WCIE GBT United Kingdom Hervé Guillou† Laboratoire des Sciences du Climat et de l’Environnement, CNRS-CEA, F-91198 Gif-sur-Yvette, France Philip Gravestock Department of Geography and Geology, Cheltenham and Gloucester College of Higher Education, United Kingdom ABSTRACT bre Vieja volcano. Interactions between erup- lowed by a period of quiescence and deep ero- tion rates, coastal erosion, and glacio-eustatic sion (erosional gap), which in turn is followed by The islands of La Palma and El Hierro form sea level change allow stratigraphic subdivi- a posterosional stage of activity (Fig. 1A). the western end of the hotspot-induced Canary sion of the edifice. The structure of the volcano In the Hawaiian Islands, Hawaii, the last is- Islands chain. Both islands are at present in the has been controlled for most of its history by a land to be formed and currently the most active, earliest and fastest shield-building stage of rift system with a clearly dominant north- is the most intensely studied. In contrast, little ge- growth and show many similarities with the south and less-distinct north-east and north- ological information has been available for the Hawaiian Islands. La Palma shows two very west volcanic rift zones. The rift reorganiza- youngest and most active of the Canary Islands, distinct phases of volcanic construction: (1) a tion of the volcano to a single north-south rift La Palma and El Hierro, which are commonly re- Pliocene submarine volcanic and intrusive se- since 7 ka and the opening of faults during the ferred to as the lesser Canaries. However, it is ries, interpreted as an uplifted seamount at 1949 eruption probably reflect increasing in- precisely in these youngest islands where it is least 1500 m above present sea level, and (2) a stability of the west flank of the volcano. possible to observe features critical to the under- subaerial volcanic series erupted in the past 2 standing of the genesis and development of the m.y. Taburiente volcano initially formed the INTRODUCTION AND archipelago, which are difficult to identify in the northern part of the island and then extended GEOLOGICAL FRAMEWORK older, posterosional islands. to the south, forming a ridge (Cumbre Nueva This trend has changed in the past few years. Ridge) that was partially destroyed about The Canary Island archipelago is one of the There has been a spectacular increase in the 560 ka by a giant lateral collapse (the Cumbre most extensively studied groups of oceanic is- number of published radiometric ages for the Nueva collapse), possibly involving 180–200 lands in the world. This archipelago is close to western islands (Fig. 1B): from 4, for El Hierro, km3 of subaerial volcanic material. The north- the passive continental margin of northwest and 8, for La Palma (Abdel-Monem et al., 1972), west boundary of the Cumbre Nueva collapse Africa and has developed over the past 30 m.y. to 30 and 70, respectively, at present (Staudigel formed a vertical scarp that, enlarged by head- as a result of the slow east to west movement of et al., 1986; Ancochea et al., 1994; Guillou et al., ward erosion, formed the spectacular depres- a mantle hotspot (Holik et al., 1991; Hoernle 1996, 1997). The precision of these ages has sion of Caldera de Taburiente. Cumbre Vieja et al., 1991; Canas et al., 1995; Carracedo, 1996; been greatly improved (Guillou et al., 1996, volcano, a north-south elongated rift, forms Carracedo et al., 1997a, 1998). The stages of de- 1997) by using samples collected in stratigraphic the southern half of La Palma and constitutes velopment of the Canary Islands show many sequences, separating out microcrystalline its last stage of growth, including all eruptive similarities to other hotspot-related island groundmass for K and Ar analysis and using an activity in the past 125 k.y. Detailed field ob- groups, such as the Hawaiian Islands and the unspiked K-Ar technique (Cassignol et al., 1978) servations, mapping, and high-precision radio- Réunion group (Carracedo et al., 1997a). to determine the isotopic composition of Ar and metric dating have allowed reconstruction of Quaternary igneous activity in the Canary Is- Ar content with a precision of 0.4% ( ± 2σ). The the growth and structural changes of the Cum- lands is concentrated at the western end of the results are then cross-correlated with the magne- archipelago, close to the present-day location of tostratigraphy defined by field and laboratory measurements and with stratigraphic constraints *E-mail: [email protected]. the inferred hotspot. Individual islands in the Ca- †Corresponding author; e-mail: herve.guillou@cfr naries, as in Hawaii, are characterized by initial from onshore and offshore mapping. .cnrs-gif.fr. rapid growth (the shield-building stage), fol- Recent sidescan sonar (GLORIA and TOBI) GSA Bulletin; May 1999; v. 111; no. 5; p. 755–768; 11 figures. 755 Downloaded from http://pubs.geoscienceworld.org/gsa/gsabulletin/article-pdf/111/5/755/3383233/i0016-7606-111-5-755.pdf by guest on 28 September 2021 Figure 1. Age relationships in the Canary Islands. (A) Oldest dated subaerial volcanism (in Ma). The youngest islands (in black) are in the shield-building stage of growth. (B) Radiometric ages obtained from the different Canarian Islands. Geochrono- logical data for the western is- lands have improved dramati- cally; about 100 of the 450 ages determined from volcanic rocks of the Canary Islands correspond to La Palma and El Hierro. 756 Geological Society of America Bulletin, May 1999 Downloaded from http://pubs.geoscienceworld.org/gsa/gsabulletin/article-pdf/111/5/755/3383233/i0016-7606-111-5-755.pdf by guest on 28 September 2021 VOLCANIC EVOLUTION OF LA PALMA, CANARY ISLANDS and swath bathymetric mapping around the west- ern Canary Islands (Holcomb and Searle, 1991; Masson and Watts, 1995; Masson, 1996) has demonstrated the importance of giant lateral col- lapses in the evolution of these islands, corrobo- rating evidence obtained in the contemporary on- shore studies. In this work we present the results of detailed volcanological and structural field observations of the last stages of development of the Taburi- ente volcano (the Cumbre Nueva Ridge) and the Cumbre Vieja volcano. These observations and 31 new (Guillou et al., 1997) high-precision ra- diometric ages (29 K-Ar and 2 14C) allow us to reconstruct the relevant events in the most recent stages of evolution of the island of La Palma. The Caldera de Taburiente is the most spectac- ular topographic feature of La Palma, a 15-km- long and 6-km-wide depression, to 2 km deep, with precipitous bounding cliffs on most sides and a deeply dissected floor. Charles Lyell (1855) considered Caldera de Taburiente as the prototypical erosion caldera. The caldera, as it is named, supplied Lyell with the term “caldera,” to which he gave a general application. However, the genetic meaning of the word “caldera” has changed so completely in more recent years, we consider the claim of the Caldera de Taburiente to be the type caldera to have lapsed. Caldera de Taburiente is not an erosion caldera but a large depression initiated by a giant gravitational col- lapse later enlarged by retrogressive erosion. Herein, we refer to it by its proper name and not as “the caldera,” which is a practice that causes confusion. GEOLOGY OF LA PALMA The island of La Palma is the second-youngest and westernmost island of the Canary Island Archipelago (Fig. 1, A and B). La Palma is cur- rently in the shield-building stage of growth and is the fastest-growing island in the archipelago. Recent activity is concentrated on the southern part of the island, at Cumbre Vieja volcano, where six historic (post A.D. 1500) eruptions, in- cluding the last one in 1971, were located. Staudigel (1981) and Staudigel and Schmincke (1984) defined two main geologic units: (1) a Pliocene submarine and plutonic basement com- plex, exposed in the walls of the Caldera de Figure 2. Sketch of the island of La Palma showing the main geologic units and features re- Taburiente (to 1500 m above present sea level) and ferred to in the text. For latitude and longitude, see Figure 1. interpreted by these authors as an uplifted seamount; and (2) subaerial lavas that uncon- formably overlie the seamount. The subaerial vol- of La Palma. More specifically, we examine the GEOCHRONOLOGY canic rocks compose three successive volcanoes period from the last collapse of the Taburiente (Fig. 2): Taburiente volcano, Bejenado volcano, volcano to the growth of Cumbre Vieja volcano. There have been 29 new K-Ar ages deter- and Cumbre Vieja volcano. The most recent events, which indicate incipient mined for lavas of Taburiente volcano (853 ± 10 In this work we consider the subaerial stage of instability of the western flank of Cumbre Vieja, ka to 566 ± 8 ka) and for basic lavas and phono- growth and partial destruction by lateral collapse will be considered in a separate paper. lite domes of Cumbre Vieja volcano (123 ± 3 ka Geological Society of America Bulletin, May 1999 757 Downloaded from http://pubs.geoscienceworld.org/gsa/gsabulletin/article-pdf/111/5/755/3383233/i0016-7606-111-5-755.pdf by guest on 28 September 2021 CARRACEDO ET AL.