lournalofvolcanology hndgeothermalresefrch ffiEI-SEVIER Journal of Volcanology and Geothermal Research94 (1999) I-I9 www.elsevier.com/locaIe / jv olgeorcs Growth,structure, instability and collapse of Canarianvolcanoes andcomparisons with Hawaiianvolcanoes JuanCarlos Carracedo . Estaci6nvotcanol6sica de Canarias(|PNA), Consejo CientiJicas(CSIO, 38206La Laguna,renerife, Y,,T;;:,rr:;:,r'rrrr::iones Received10 Mav 1999 Abstract Recentonshore and offshoreinvestigations in the Canarianarchipelago, especially in the westernislands of La Palma and El Hieno, have greatly improved the understandingof the genesisand evolution of these islands and allow interesting comparisonswith other hotspot-inducedoceanic island volcanoes,especially the Hawaiian archipelago.Genesis induced by I hotspot activity and, consequently,shield and post-erosionalstages of growth allow the definition of similar main stratigraphicunits. The Canarianand Hawaiian volcanoesshow common constructionaland structuralfeatures, such as rift zones,progressive volcano instability and multiple gravitationalcollapses. However, the Canariespresent some important geological differences from the prototypical hotspot volcanoes of the Hawaiian Islands, particularly the absenceof significantsubsidence; The Canarianvolcanoes remain emergentuntil completely mass-wastedby gravitationalcollapses and erosion.Volcanic formationsover 20 million years are observablein outcrop in the Canaries,including the seamount stagesof growth in severalof the islands.O 1999 Elsevier ScienceB.V. All rights reserved. Keywords:Canary Islands; Hawaiian Islands; oceanic islands; comparative volcanism and structure 1. Introduction readily distinguishablehotspot signature (a clear hotspot trace, mantle anomaly and swell), generated Apart from the Hawaiian Islands,the Canariesare on a fast-movingplate (Wilson, 1963;Morgan,1972 probablyone of the most extensivelystudied groups Clagueand Dalrymple, 1987;Walker, 1990);and (2) of hotspot-generatedoceanic islands in the world. the Canaries, where the hotspot signature is geo- The comparison of the Hawaiian and Canarian chemically and geophysically less evident and the 'olcanoes leads to some interestins clarifications. plate velocity is lower by about an order of magni- h archipelago representsa distinctly characteris- tude (Filmer and Mcnutt, 1988; Hoernle and ic hotspot-inducedoceanic group: (1) the Hawaiian Schmincke, 1993; Canaset al., 1994; Watts, 1994). hipelago,the prototypical hotspot islands,with a There are several specific advantagesin the Ca- naries for the study of the processesand patterns of development, the structure, instability, and collapse of island volcanoes that are difficult to investigate ' E-mail: jcarracedo@ ipna.csic.es fully in other oceanic groups. Perhaps, the only r1'l-0273/99/$ - see front matter O 1999 Elsevier ScienceB.V. All riehts reserved. I: 503'17-0273 (99)00095-5 J.C. Carraceda / Journal ofVolcanology and Geotherrnal Research 94 (199q 1-19 similarly-advantaged group is the Cape Verde Is- islands of La Palma and Tenerife and, to a lesser lands; unfortunately, the geology and geochronology extent, El Hierro (Carracedo,1994). of these remote islands are relatively little known. In this paper we review some important features The individual islands of the Hawaiian archipelago of the growth, structure, progressive instability and have a relatively short lifespan: high-rate subsidence flank collapse of the Canarian volcanoes and their (as quoted by Moore, 1987, most of the Hawaiian comparison with other oceanic volcanoes, especially volcaroes have subsided 2-4 kJ\ since emergence) those of the Hawaiian Islands. precludes the islands from continuing above sea level after only a few million years (Moore and Fornari, 1984; Moore, 1987; Moore and Thomas, 2. Growth of the Canarian volcanoes 1988; Walker, 1990). Kauai, the oldest emerged island in the Hawaiian chain, is less than 6 Ma 2.l. Geochronology and stratigraphy (McDougall, 1964, 19'79).Thus, only the relatively young parts of the islands are exposed to observa- The first comprehetsive stratigraphy of the Ca- tion. High rainfall gives rise to a dense vegetation naries was compiled by Ffster et al. (1968a,b,c,d)for screen and rapid weathering of rocks, making expo- the islands of Lanzarote. Fuerteventura. Gran Ca- suresrelatively scarce.Thus, geological observations naria and Tenerife. Numbered stratigraphic series (I as well as radiometric dating and magnetic stratigra- to IV) were defined by the presence of a general phy are difficult in many areas, increasing the diffi- erosional unconformity and interbedded fossil culty of the complete reconstruction of these volca- beaches.Absolute dating of the volcanic formations noes (McDoryall, 1963, 1964, 1969, 1971, 1979; using radiometric (K/Ar) and palaeomagnetictech- McDougall and Tarling, 1963; McDougall and Ur- niques (Abdel-Monem et al., 1971,1972; McDougall Rahman, 1972; McDougall and Swanson, 1972;Hol- and Schmincke, 1976; Canacedo, 1979) made it comb, 1980; Naughton et al., 1980; Clague and clear that the stratigraphy defined was not applicable Dalrymple, 1987; Holcomb et al., 1997). to all the Canaries. In contrast, there is no comparable subsidencein The term "Series" used by Ffster et al. con- the Canaries, as discussed below. Volcanic forma- formed to the stratigraphic code in use at the time. tions over 20 Ma are observable in outcrop, includ- However, it does not conform to the present code ing the seamount stages of growth in several of the (NACSN, 1983), which restricts the use of this term islands, as discussedlater. Since all the Canaries are to geological units formed during the sametime-span. still emergent above sea level, it is feasible to study with synchronousboundaries. Recently impro in outcrop volcanic formations and structures over a geochronological (radiometric and palaeomagnet wide range of ages and original emplacementdepths, data reinforced these ideas (Ancochea et al., I according to the age of the islands and the different 1994:Guillou et al.. 1996.1998: Carracedo et al stagesof erosive mass-wasting.The vegetation cover 1999-this volume) suggesting to find a more is comparatively poor and the lavas have a high K priate stratigraphic definition for the Canaries. content, favouring geochronological (K/Ar and Fig. 1 presentsa plot of the publishedK/ Ar palaeomagnetic reversals) determinations (Abdel- from lava flows of the Canarian and the Hawaii Monem et al., L97I, 1972; McDougall and islands. When compared, we can easily see Schmincke, t976; Cartacedo, 1979; Ancochea et al., individual islands in both archipelagos show 1990, 1994, 1996; Coello et a1.,1992; Guillou et al., main stages of growth separatedby periods of 1996,1998; Caracedo et al., 1999-thisvolume). The canic repose (gaps). The combined use of pa high population and the absence of surface waters on magnetic reversalsand radiometric dating has the islands have necessitatedthe mining of ground- to be efficient in the Hawaiian Islands (Holcomb water by means of more than 3000 km of sub-hori- al.. 1997) and the Canaries (Abdel-Monem et zontal tunnels (locally known as "galerias"), which 1971,1972; Carracedo, 1979; Cnracedoand allow the observation of the internal structure of the 1995: P6rez Torrado et a1., 1995: Guillou et volcanoes at almost any point and depth in the 1996) in defining the presence of eruptive gaps E J.C. Canacedo / Journal of Volcanology and Geothermnl Research 94 ( I99q I -19 d the Ca )fc Gran C& series(l d a generd fossil formatior EL HIERRO I.A GOMERA GRANCAMRIA LANZAROTE LA PALMA TENERIFE FUERTEVENTURA ic tecb A) made not appli 5.8 a Old shield-stage tl volcanisy___ ---1> tl et al. LJ at the present nse of this GAP satne tlme /\"-1 / et al., I I Carracedo et Shr€/d-stage I Islend a more t, Canaries n,J- I K/N i:; T - ""t""r-"rlr"r.rr, and the volca easily see HAWAII MAUI I-ANAI MOLOKAI OAHU KAUAI NIIHAU ipelagos show Shield- -+ I by periods of stage Post-erosionalstage islands ined use of islands ric dating has B) Islands ( tMel-Monem et Fig. 1. Published K/Ar ages from lavas of the Canary Islands (A) and the Hawaiian Islands (B). The presence of a gap in the eruptive activity allows the separation in both archipelagos posterosional-stage brracedo and of two main stratigraphic units: Shield stage and volcanism. Hawaiian ages from (1987). (1971; (1976), et are Clague and Dalrymple Canarian ages are from Abdel-Monem et al. 1972), McDougall and Schmincke 995; Guillou Carracedo (1979), Ancochea et al. (1990,1994,1996), Coello et al. (1992), Guillou et al. (1996, 1998) and P6rez Torrado et al. (1995). of eruptive X-axis not to scale. I I 4 J.C. Carracedo / Journal of VolcanoLog,-and Geothermal Research 94 ( I ggg) I - I g I (as hiatuses shown in Fig. 1) rather than sampling This feature was used in the Hawaiian Islands to f gaps. separatetwo main units (Fig. 2A) of generaluse in I I ost-erosional I Shield stage I I ,u"] i I I1.1 I Post-s h ie ldt gap A) |,:, j.., I the archipe or post-el Fig. 2. A mai island, which Shieldstage with a hotspo Gomera and I while in the F Tenerife) are Abdel-Monen I ( 1996). I I h* 94 ( 1999) I - I 9 J.C Carracedo / Journal of Volcanology and Geothermal Research of the Canary lslands aiian Islands Sequentialsurfacing 56 Fig. 3. Sequential surfacing of the Canary Islands. Explanation in the text' the archipelago:the shield stage and the reiuuenated 1987;Langenheim and Clague,1987; Walker, 1990). Canaries, or post-erosional stage (Clagve and DalrymPle, This division is easily applicable