- Email: [email protected]
Ar, morphologic, tectonic, and magnetic data: The Faial Island example (Azores)” by Hildenbrand et al. (2012) [J. Volcanol. Geotherm. Res. 241–242 (2012) 39–48]
Journal of Volcanology and Geothermal Research 255 (2013) 124–126
Contents lists available at SciVerse ScienceDirect
Journal of Volcanology and Geothermal Research journal homepage: www.elsevier.com/locate/jvolgeores
Discussion
Comment on “Reconstructing the architectural evolution of volcanic islands from combined K/Ar, morphologic, tectonic, and magnetic data: The Faial Island example (Azores)” by Hildenbrand et al. (2012) [J. Volcanol. Geotherm. Res. 241–242 (2012) 39–48] Rui Quartau a,⁎, Neil C. Mitchell b a b
Unidade de Geologia Marinha, Laboratório Nacional de Energia e Geologia. Estrada da Portela, Bairro do Zambujal, Apartado 7586-Alfragide, 2610-999 Amadora, Portugal School of Earth, Atmospheric and Planetary Sciences, University of Manchester, Williamson Building, Oxford Road, Manchester M13 9PL, UK
a r t i c l e
i n f o
Article history: Received 20 September 2012 Accepted 22 December 2012 Available online 17 January 2013
Keywords: Faial Island Multibeam bathymetry Volcanic island evolution Ridge-like morphology Insular shelf Mass-wasting
a b s t r a c t Hildenbrand et al. (2012) have presented a model for the geological evolution of Faial Island. In their interpretation, the oldest volcanic system extended much further than the present-day eastern part of the subaerial island, with a ridge-like morphology, into the Faial–S. Jorge channel. Furthermore, the western side of the system was suggested to have been later destroyed by mass-wasting. Based on now extensive multibeam bathymetry collected surrounding Faial Island, we find no evidence supporting such interpretations. The geometry of the shelf edge suggests that a near-circular edifice occupied the eastern part of the present-day subaerial island. In addition, the submarine morphology does not show massive mass-wasting deposits around the base of the edifice. Rather, bathymetric gradients and morphology suggest that the submarine slopes were formed from volcanic emplacements or from material displaced in only small-scale mass-movements or sedimentary flows, and have not failed catastrophically. Evidence that a ridge-like feature extended into the Faial–S. Jorge channel is also lacking. These observations highlight the potentially valuable information that sonar data can provide to evaluating ocean island evolution from the more limited extend of outcrops on land. © 2013 Elsevier B.V. All rights reserved.
The recently published multi-disciplinary study of Hildenbrand et al. (2012) has improved the understanding of the subaerial geological evolution of Faial Island. However, volcanic islands are like icebergs, in that the majority of their volumes lie hidden beneath sea level, so efforts are needed to characterize them underwater as well as on land to more fully understand their evolution. This approach has been proved successful in studies of several volcanic ocean island groups around the world (e.g. Favalli et al., 2005; Gee et al., 2001; Masson et al., 2002; Mitchell et al., 2002; Oehler et al., 2008; Mitchell et al., 2012). A better consideration of evidence including submarine data is illustrated by problems in the study of Hildenbrand et al. (2012). We were especially concerned about their claim that the oldest volcanic system (their Fig. 6a) was in the past geographically similar to the presentday island area. They support this interpretation based on the reversed polarity measured on lava flows of this volcanic complex, which only crop out on the east side of the island and negative magnetization anomalies in the different sectors of Faial Island (except the SW). The old edifice was accordingly formed during the final stages of the
DOI of original article: http://dx.doi.org/10.1016/j.jvolgeores.2013.01.015. ⁎ Corresponding author. Tel.: +351 967193230. E-mail address: [email protected] (R. Quartau). 0377-0273/$ – see front matter © 2013 Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.jvolgeores.2012.12.020
Matuyama reversed chron and the negative anomalies reflected the wide extension of the edifice hidden by a thin cover of the more recent volcanic complexes formed already in the Brunhes normal chron. The almost absence of this old volcanic system on the cliffs is explained by erosion, such as by mass-wasting, coastal and stream erosion. They further suggest a ridge-like morphology for this volcanic system that extends into the Faial–S. Jorge channel as proposed by Miranda et al. (1991). Based on previously published multibeam sonar data collected around Faial Island (Mitchell et al., 2003b; Quartau et al., 2010, 2012) several lines of evidence allow us to argue against that interpretation: 1. Insular shelves are formed by wave erosion during eustatic changes in sea level. Therefore, shelf morphology (especially the position of the shelf edge) in young volcanic islands where erosion dominates can help to constrain the chronology of the volcanic emplacements (Quartau et al., 2010, 2012). When wave erosion dominates over other processes (as is the case of Faial — Quartau et al., 2010), shelf width increases with edifice age (Menard, 1983; Ablay and Hurlimann, 2000; Le Friant et al., 2004; Llanes et al., 2009). The geometry of the shelf edge thus helps to delimit the original shapes of the edifices and to evaluate the sequence of volcanic growth. Semi-circular edifices can be roughly interpreted from the data as shown in Fig. 1 where the shelf edge (dashed red line)
R. Quartau, N.C. Mitchell / Journal of Volcanology and Geothermal Research 255 (2013) 124–126
125
Fig. 1. Offshore: shaded relief imagery derived from the bathymetric compilation. Black line depicts the coastline and red dashed line the shelf edge. Onshore: shaded relief topography of Faial Island. Blue and yellow circles represent respectively the old and the central volcanic edifices of Faial Island based on the position of the shelf edge and subaerial information in Madeira and Brum da Silveira (2003). Black ellipse represents the dimension of a hypothetically ridge-like volcanic edifice based on the position of the shelf edge (two small circles) and its WNW–ESE trend. Black arrows on the west locate three small volcanic ridges. Black fine polygon delimits the bathymetry analyzed in Fig. 2.
would be compatible with an approximately circular shape of the oldest volcanic complex (blue circle in Fig. 1). The eastern part of the central volcano (yellow circle in Fig. 1) would also be compatible with the shelf edge geometry, whereas the lack of correspondence in the west, in this interpretation, would need to have been destroyed by relatively small slope failure. A ridge-like edifice suggested by Hildenbrand et al. (2012) would need to follow the limits of what is the present-day shelf edge (we used two points of the shelf edge and the WNW–ESE trend of the island to position the black ellipse in Fig. 1), but it is difficult to find evidence of such a broad feature. Although not all volcanic edifices are necessarily circular or semicircular, of course, the bathymetry data provide morphologic evidence that need to be reconciled with the subaerial information to help explain the sequence of island building. 2. The analysis of the shape of submarine flanks of volcanic islands in profile can indicate the nature of the processes constructing and modifying their flanks (Lee et al., 1994; Gee et al., 2001; Masson et al., 2002; Mitchell et al., 2002). In particular, the research on the Canary Islands has allowed us to get a good sense of whether an area has failed catastrophically in the past (debris avalanche type). These areas tend to produce smooth chutes of gradually varying gradient with depth, accompanied with a debris field below (Mitchell et al., 2003a). The surface is often almost an exact exponential curve (Gee et al., 2001) with gradients normally below 10° declining
systematically with depth (Mitchell et al., 2003a). In contrast, volcanic construction slopes tend to be much steeper, with a more rugged morphology, with gradients reaching 30°, the angle of repose of rock talus underwater (Lee et al., 1994; Mitchell et al., 2000). The exception might be a slump, such as the Hilina Slump of Kilauea, where one can find benches within the slope (Smith et al., 1999). Fig. 2 shows how the average slope (50%) and the slope variability (inter-quartile range, respectively 25% and 75%) change with depth within the area polygon outlined by the fine line surrounding the Faial bathymetry in Fig. 1. From the coastline to around 100 m below sea level, median gradients vary between 2° and 5° representing the smooth bathymetry of the shelf. Between 100 m and 120 m depth, seafloor median gradients increase sharply to 15°, marking the transition from the shelf to the slope. The zigzagging between 120 m and 200 m depth is due to common slumping that occurs at the shelf edge (Quartau et al., 2010, 2012). Below 200 m depth, median gradients increase sharply to almost 25° at 270 m. Below 270 m depth, gradients decrease smoothly with depth, reaching 2° at around 800 m, representing the bathymetric base of the Faial volcanic edifice. The zigzagging of gradients between 2° and 7° below 800 m depth corresponds to volcanic ridges and some isolated volcanic cones around Faial submarine edifice. The smooth topography of the area between 270 m and 800 m depth probably reflects volcanic debris-mantled slopes formed by fragmentation of lava
126
R. Quartau, N.C. Mitchell / Journal of Volcanology and Geothermal Research 255 (2013) 124–126
can potentially provide a much stronger case for resolving the evolution of a volcanic island. We urge greater efforts to combine geological studies on land with information from submarine datasets such as these, because often the offshore data provide information not obvious above sea level (Masson et al., 2002) and are thus critical to evaluating the hazards of volcanic islands. References
Fig. 2. Gradients calculated from the bathymetric mosaic. The dashed line represents the median (50%) and the solid lines the inter-quartile range (25% and 75%) of the seabed gradient, calculated as in Mitchell et al. (2002). Graph was calculated by sorting gradients into depth intervals of 10 m, and deriving a slope cumulative distribution for each depth interval (plotting the 25%, 50% and 75% levels of that distribution).
entering the sea and the products of coastal and subaerial erosion. They are typical examples of volcanic constructional flanks. It is though, difficult to support the massive erosion of the old volcanic edifice of Faial suggested by Hildenbrand et al. (2012) because there is no evidence of mass-wasting deposits around the submarine base of the edifice, chutes or exponential profile; rather the pattern of bathymetric gradients and morphology are more simply explained by the processes inferred in the better studied "constructional" areas in the Canary and other island groups. 3. The ridge-like morphology of the old volcanic system is not confirmed by our analysis of the bathymetry west of Faial. There is a well defined volcanic ridge west of Capelinhos which links to the onshore structure and is paralleled by two other small ridges further north (see arrows in Fig. 1) that are isolated from the subaerial island. Nevertheless, there is no significant evidence for the old volcanic system to be interpreted as a major ridge-like edifice extending into the Faial-S. Jorge channel. The discussion outlined here will hopefully illustrate the range of useful information available from modern multibeam echo-sounders, including surface morphology, rate of change of gradient with depth and shape of the shelf. Reconciling these with the onshore geology
Ablay, G., Hurlimann, M., 2000. Evolution of the north flank of Tenerife by recurrent giant landslides. Journal of Volcanology and Geothermal Research 103, 135–159. Favalli, M., Karátson, D., Mazzuoli, R., Pareschi, M., Ventura, G., 2005. Volcanic geomorphology and tectonics of the Aeolian archipelago (Southern Italy) based on integrated DEM data. Bulletin of Volcanology 68 (2), 157–170. Gee, M.J.R., Watts, A.B., Masson, D.G., Mitchell, N.C., 2001. Landslides and the evolution of El Hierro in the Canary Islands. Marine Geology 177, 271–293. Hildenbrand, A., et al., 2012. Reconstructing the architectural evolution of volcanic islands from combined K/Ar, morphologic, tectonic, and magnetic data: the Faial Island example (Azores). Journal of Volcanology and Geothermal Research 241–242, 39–48. Le Friant, A., et al., 2004. Geomorphological evolution of Monserrat (West Indies): importance of flank collapse and erosional processes. Journal of the Geological Society 161, 147–160. Lee, H.J., Torresan, M.E., McArthur, W., 1994. Stability of submerged slopes on the flanks of the Hawaiian islands, a simplified approach. Open File Report 94-638. U.S. Geological Survey, Menlo Park, California. Llanes, P., et al., 2009. Geological evolution of the volcanic island La Gomera, Canary Islands, from analysis of its geomorphology. Marine Geology 264 (3–4), 123–139. Madeira, J., Brum da Silveira, A., 2003. Active tectonics and first paleosismological results in Faial, Pico e S. Jorge islands (Azores, Portugal). Annals of Geophysics 46 (5), 733–761. Masson, D.G., et al., 2002. Slope failures on the flanks of the western Canary Islands. Earth-Science Reviews 57 (1–2), 1–35. Menard, H.W., 1983. Insular erosion, isostasy, and subsidence. Science 220, 913–918. Miranda, J.M., et al., 1991. Tectonic framework of the Azores Triple Junction. Geophysical Research Letters 18 (8), 1421–1424. Mitchell, N.C., Tivey, M.A., Gente, P., 2000. Seafloor slopes at mid-ocean ridges from submersible observations and implications for interpreting geology from seafloor topography. Earth and Planetary Science Letters 183, 543–555. Mitchell, N.C., Masson, D.G., Watts, A.B., Gee, M.J.R., Urgeles, R., 2002. The morphology of the flanks of volcanic ocean islands: a comparative study of the Canary and Hawaiian hotspot islands. Journal of Volcanology and Geothermal Research 115, 83–107. Mitchell, N.C., Dade, W.B., Masson, D.G., 2003a. Erosion of the submarine flanks of the Canary Islands. Journal of Geophysical Research 108 (F1), 3-1–3-11. Mitchell, N.C., et al., 2003b. Multibeam sonar survey of the central Azores volcanic islands. InterRidge News 12 (2), 30–32. Mitchell, N.C., Quartau, R., Madeira, J., 2012. Assessing landslide movements in volcanic islands using near-shore marine geophysical data: south Pico Island, Azores. Bulletin of Volcanology 74 (2), 483–496. Oehler, J.-F., Lénat, J.-F., Labazuy, P., 2008. Growth and collapse of the Reunion Island volcanoes. Bulletin of Volcanology 70 (6), 717–742. Quartau, R., Trenhaile, A.S., Mitchell, N.C., Tempera, F., 2010. Development of volcanic insular shelves: Insights from observations and modelling of Faial Island in the Azores Archipelago. Marine Geology 275 (1–4), 66–83. Quartau, R., et al., 2012. Morphology of the Faial Island shelf (Azores): the interplay between volcanic, erosional, depositional, tectonic and mass-wasting processes. Geochemistry, Geophysics, Geosystems 13, Q04012. http://dx.doi.org/10.1029/2011GC003987. Smith, J.R., Malahoff, A., Shor, A.N., 1999. Submarine geology of the Hilina slump and morpho-structural evolution of Kilauea volcano, Hawaii. Journal of Volcanology and Geothermal Research 94, 59–88.
Contents lists available at SciVerse ScienceDirect
Journal of Volcanology and Geothermal Research journal homepage: www.elsevier.com/locate/jvolgeores
Discussion
Comment on “Reconstructing the architectural evolution of volcanic islands from combined K/Ar, morphologic, tectonic, and magnetic data: The Faial Island example (Azores)” by Hildenbrand et al. (2012) [J. Volcanol. Geotherm. Res. 241–242 (2012) 39–48] Rui Quartau a,⁎, Neil C. Mitchell b a b
Unidade de Geologia Marinha, Laboratório Nacional de Energia e Geologia. Estrada da Portela, Bairro do Zambujal, Apartado 7586-Alfragide, 2610-999 Amadora, Portugal School of Earth, Atmospheric and Planetary Sciences, University of Manchester, Williamson Building, Oxford Road, Manchester M13 9PL, UK
a r t i c l e
i n f o
Article history: Received 20 September 2012 Accepted 22 December 2012 Available online 17 January 2013
Keywords: Faial Island Multibeam bathymetry Volcanic island evolution Ridge-like morphology Insular shelf Mass-wasting
a b s t r a c t Hildenbrand et al. (2012) have presented a model for the geological evolution of Faial Island. In their interpretation, the oldest volcanic system extended much further than the present-day eastern part of the subaerial island, with a ridge-like morphology, into the Faial–S. Jorge channel. Furthermore, the western side of the system was suggested to have been later destroyed by mass-wasting. Based on now extensive multibeam bathymetry collected surrounding Faial Island, we find no evidence supporting such interpretations. The geometry of the shelf edge suggests that a near-circular edifice occupied the eastern part of the present-day subaerial island. In addition, the submarine morphology does not show massive mass-wasting deposits around the base of the edifice. Rather, bathymetric gradients and morphology suggest that the submarine slopes were formed from volcanic emplacements or from material displaced in only small-scale mass-movements or sedimentary flows, and have not failed catastrophically. Evidence that a ridge-like feature extended into the Faial–S. Jorge channel is also lacking. These observations highlight the potentially valuable information that sonar data can provide to evaluating ocean island evolution from the more limited extend of outcrops on land. © 2013 Elsevier B.V. All rights reserved.
The recently published multi-disciplinary study of Hildenbrand et al. (2012) has improved the understanding of the subaerial geological evolution of Faial Island. However, volcanic islands are like icebergs, in that the majority of their volumes lie hidden beneath sea level, so efforts are needed to characterize them underwater as well as on land to more fully understand their evolution. This approach has been proved successful in studies of several volcanic ocean island groups around the world (e.g. Favalli et al., 2005; Gee et al., 2001; Masson et al., 2002; Mitchell et al., 2002; Oehler et al., 2008; Mitchell et al., 2012). A better consideration of evidence including submarine data is illustrated by problems in the study of Hildenbrand et al. (2012). We were especially concerned about their claim that the oldest volcanic system (their Fig. 6a) was in the past geographically similar to the presentday island area. They support this interpretation based on the reversed polarity measured on lava flows of this volcanic complex, which only crop out on the east side of the island and negative magnetization anomalies in the different sectors of Faial Island (except the SW). The old edifice was accordingly formed during the final stages of the
DOI of original article: http://dx.doi.org/10.1016/j.jvolgeores.2013.01.015. ⁎ Corresponding author. Tel.: +351 967193230. E-mail address: [email protected] (R. Quartau). 0377-0273/$ – see front matter © 2013 Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.jvolgeores.2012.12.020
Matuyama reversed chron and the negative anomalies reflected the wide extension of the edifice hidden by a thin cover of the more recent volcanic complexes formed already in the Brunhes normal chron. The almost absence of this old volcanic system on the cliffs is explained by erosion, such as by mass-wasting, coastal and stream erosion. They further suggest a ridge-like morphology for this volcanic system that extends into the Faial–S. Jorge channel as proposed by Miranda et al. (1991). Based on previously published multibeam sonar data collected around Faial Island (Mitchell et al., 2003b; Quartau et al., 2010, 2012) several lines of evidence allow us to argue against that interpretation: 1. Insular shelves are formed by wave erosion during eustatic changes in sea level. Therefore, shelf morphology (especially the position of the shelf edge) in young volcanic islands where erosion dominates can help to constrain the chronology of the volcanic emplacements (Quartau et al., 2010, 2012). When wave erosion dominates over other processes (as is the case of Faial — Quartau et al., 2010), shelf width increases with edifice age (Menard, 1983; Ablay and Hurlimann, 2000; Le Friant et al., 2004; Llanes et al., 2009). The geometry of the shelf edge thus helps to delimit the original shapes of the edifices and to evaluate the sequence of volcanic growth. Semi-circular edifices can be roughly interpreted from the data as shown in Fig. 1 where the shelf edge (dashed red line)
R. Quartau, N.C. Mitchell / Journal of Volcanology and Geothermal Research 255 (2013) 124–126
125
Fig. 1. Offshore: shaded relief imagery derived from the bathymetric compilation. Black line depicts the coastline and red dashed line the shelf edge. Onshore: shaded relief topography of Faial Island. Blue and yellow circles represent respectively the old and the central volcanic edifices of Faial Island based on the position of the shelf edge and subaerial information in Madeira and Brum da Silveira (2003). Black ellipse represents the dimension of a hypothetically ridge-like volcanic edifice based on the position of the shelf edge (two small circles) and its WNW–ESE trend. Black arrows on the west locate three small volcanic ridges. Black fine polygon delimits the bathymetry analyzed in Fig. 2.
would be compatible with an approximately circular shape of the oldest volcanic complex (blue circle in Fig. 1). The eastern part of the central volcano (yellow circle in Fig. 1) would also be compatible with the shelf edge geometry, whereas the lack of correspondence in the west, in this interpretation, would need to have been destroyed by relatively small slope failure. A ridge-like edifice suggested by Hildenbrand et al. (2012) would need to follow the limits of what is the present-day shelf edge (we used two points of the shelf edge and the WNW–ESE trend of the island to position the black ellipse in Fig. 1), but it is difficult to find evidence of such a broad feature. Although not all volcanic edifices are necessarily circular or semicircular, of course, the bathymetry data provide morphologic evidence that need to be reconciled with the subaerial information to help explain the sequence of island building. 2. The analysis of the shape of submarine flanks of volcanic islands in profile can indicate the nature of the processes constructing and modifying their flanks (Lee et al., 1994; Gee et al., 2001; Masson et al., 2002; Mitchell et al., 2002). In particular, the research on the Canary Islands has allowed us to get a good sense of whether an area has failed catastrophically in the past (debris avalanche type). These areas tend to produce smooth chutes of gradually varying gradient with depth, accompanied with a debris field below (Mitchell et al., 2003a). The surface is often almost an exact exponential curve (Gee et al., 2001) with gradients normally below 10° declining
systematically with depth (Mitchell et al., 2003a). In contrast, volcanic construction slopes tend to be much steeper, with a more rugged morphology, with gradients reaching 30°, the angle of repose of rock talus underwater (Lee et al., 1994; Mitchell et al., 2000). The exception might be a slump, such as the Hilina Slump of Kilauea, where one can find benches within the slope (Smith et al., 1999). Fig. 2 shows how the average slope (50%) and the slope variability (inter-quartile range, respectively 25% and 75%) change with depth within the area polygon outlined by the fine line surrounding the Faial bathymetry in Fig. 1. From the coastline to around 100 m below sea level, median gradients vary between 2° and 5° representing the smooth bathymetry of the shelf. Between 100 m and 120 m depth, seafloor median gradients increase sharply to 15°, marking the transition from the shelf to the slope. The zigzagging between 120 m and 200 m depth is due to common slumping that occurs at the shelf edge (Quartau et al., 2010, 2012). Below 200 m depth, median gradients increase sharply to almost 25° at 270 m. Below 270 m depth, gradients decrease smoothly with depth, reaching 2° at around 800 m, representing the bathymetric base of the Faial volcanic edifice. The zigzagging of gradients between 2° and 7° below 800 m depth corresponds to volcanic ridges and some isolated volcanic cones around Faial submarine edifice. The smooth topography of the area between 270 m and 800 m depth probably reflects volcanic debris-mantled slopes formed by fragmentation of lava
126
R. Quartau, N.C. Mitchell / Journal of Volcanology and Geothermal Research 255 (2013) 124–126
can potentially provide a much stronger case for resolving the evolution of a volcanic island. We urge greater efforts to combine geological studies on land with information from submarine datasets such as these, because often the offshore data provide information not obvious above sea level (Masson et al., 2002) and are thus critical to evaluating the hazards of volcanic islands. References
Fig. 2. Gradients calculated from the bathymetric mosaic. The dashed line represents the median (50%) and the solid lines the inter-quartile range (25% and 75%) of the seabed gradient, calculated as in Mitchell et al. (2002). Graph was calculated by sorting gradients into depth intervals of 10 m, and deriving a slope cumulative distribution for each depth interval (plotting the 25%, 50% and 75% levels of that distribution).
entering the sea and the products of coastal and subaerial erosion. They are typical examples of volcanic constructional flanks. It is though, difficult to support the massive erosion of the old volcanic edifice of Faial suggested by Hildenbrand et al. (2012) because there is no evidence of mass-wasting deposits around the submarine base of the edifice, chutes or exponential profile; rather the pattern of bathymetric gradients and morphology are more simply explained by the processes inferred in the better studied "constructional" areas in the Canary and other island groups. 3. The ridge-like morphology of the old volcanic system is not confirmed by our analysis of the bathymetry west of Faial. There is a well defined volcanic ridge west of Capelinhos which links to the onshore structure and is paralleled by two other small ridges further north (see arrows in Fig. 1) that are isolated from the subaerial island. Nevertheless, there is no significant evidence for the old volcanic system to be interpreted as a major ridge-like edifice extending into the Faial-S. Jorge channel. The discussion outlined here will hopefully illustrate the range of useful information available from modern multibeam echo-sounders, including surface morphology, rate of change of gradient with depth and shape of the shelf. Reconciling these with the onshore geology
Ablay, G., Hurlimann, M., 2000. Evolution of the north flank of Tenerife by recurrent giant landslides. Journal of Volcanology and Geothermal Research 103, 135–159. Favalli, M., Karátson, D., Mazzuoli, R., Pareschi, M., Ventura, G., 2005. Volcanic geomorphology and tectonics of the Aeolian archipelago (Southern Italy) based on integrated DEM data. Bulletin of Volcanology 68 (2), 157–170. Gee, M.J.R., Watts, A.B., Masson, D.G., Mitchell, N.C., 2001. Landslides and the evolution of El Hierro in the Canary Islands. Marine Geology 177, 271–293. Hildenbrand, A., et al., 2012. Reconstructing the architectural evolution of volcanic islands from combined K/Ar, morphologic, tectonic, and magnetic data: the Faial Island example (Azores). Journal of Volcanology and Geothermal Research 241–242, 39–48. Le Friant, A., et al., 2004. Geomorphological evolution of Monserrat (West Indies): importance of flank collapse and erosional processes. Journal of the Geological Society 161, 147–160. Lee, H.J., Torresan, M.E., McArthur, W., 1994. Stability of submerged slopes on the flanks of the Hawaiian islands, a simplified approach. Open File Report 94-638. U.S. Geological Survey, Menlo Park, California. Llanes, P., et al., 2009. Geological evolution of the volcanic island La Gomera, Canary Islands, from analysis of its geomorphology. Marine Geology 264 (3–4), 123–139. Madeira, J., Brum da Silveira, A., 2003. Active tectonics and first paleosismological results in Faial, Pico e S. Jorge islands (Azores, Portugal). Annals of Geophysics 46 (5), 733–761. Masson, D.G., et al., 2002. Slope failures on the flanks of the western Canary Islands. Earth-Science Reviews 57 (1–2), 1–35. Menard, H.W., 1983. Insular erosion, isostasy, and subsidence. Science 220, 913–918. Miranda, J.M., et al., 1991. Tectonic framework of the Azores Triple Junction. Geophysical Research Letters 18 (8), 1421–1424. Mitchell, N.C., Tivey, M.A., Gente, P., 2000. Seafloor slopes at mid-ocean ridges from submersible observations and implications for interpreting geology from seafloor topography. Earth and Planetary Science Letters 183, 543–555. Mitchell, N.C., Masson, D.G., Watts, A.B., Gee, M.J.R., Urgeles, R., 2002. The morphology of the flanks of volcanic ocean islands: a comparative study of the Canary and Hawaiian hotspot islands. Journal of Volcanology and Geothermal Research 115, 83–107. Mitchell, N.C., Dade, W.B., Masson, D.G., 2003a. Erosion of the submarine flanks of the Canary Islands. Journal of Geophysical Research 108 (F1), 3-1–3-11. Mitchell, N.C., et al., 2003b. Multibeam sonar survey of the central Azores volcanic islands. InterRidge News 12 (2), 30–32. Mitchell, N.C., Quartau, R., Madeira, J., 2012. Assessing landslide movements in volcanic islands using near-shore marine geophysical data: south Pico Island, Azores. Bulletin of Volcanology 74 (2), 483–496. Oehler, J.-F., Lénat, J.-F., Labazuy, P., 2008. Growth and collapse of the Reunion Island volcanoes. Bulletin of Volcanology 70 (6), 717–742. Quartau, R., Trenhaile, A.S., Mitchell, N.C., Tempera, F., 2010. Development of volcanic insular shelves: Insights from observations and modelling of Faial Island in the Azores Archipelago. Marine Geology 275 (1–4), 66–83. Quartau, R., et al., 2012. Morphology of the Faial Island shelf (Azores): the interplay between volcanic, erosional, depositional, tectonic and mass-wasting processes. Geochemistry, Geophysics, Geosystems 13, Q04012. http://dx.doi.org/10.1029/2011GC003987. Smith, J.R., Malahoff, A., Shor, A.N., 1999. Submarine geology of the Hilina slump and morpho-structural evolution of Kilauea volcano, Hawaii. Journal of Volcanology and Geothermal Research 94, 59–88.