Syn-eruptive morphometric variability of monogenetic scoria cones Gábor Kereszturi1,2,3, Gyozo Jordan2, Károly Németh1,4 and Javier F. Dóniz-Páez5 1
Volcanic Risk Solutions, CS-INR, Massey University, Private Bag 11 222, Palmerston North, New Zealand; email:
[email protected] 2 Geological Institute of Hungary, Stefánia út 14, H-1143, Budapest, Hungary 3 Department of Geology and Mineral Deposits, University of Miskolc, Hungary 4 Geological Hazards Research Unit, King Abdulaziz University, Jeddah, Kingdom of Saudi Arabia 5 Department of Geography, University of La Laguna, Tenerife, Spain
The final publication is available at www.springerlink.com Pre-print version of the following paper: Kereszturi, G., Jordan G, Németh K, Dóniz-Páez JF (2012) Syn-eruptive morphometric variability of monogenetic scoria cones. – Bulletin of Volcanology, 74(9), pp. 2171-2185. DOI:10.1007/s00445-012-0658-1 Introduction Morphometric studies of volcanoes commonly aim to characterize a wide range of eruptive and erosionrelated processes (Inbar et al., 2011; Grosse et al., 2012). Scoria (or cinder) cones are one of the most frequent targets of such studies (Favalli et al., 2009; Bemis et al., 2011; Rodriguez-Gonzalez et al., 2012) due to their abundance on the Earth, occurring in monogenetic volcanic fields in almost all known geological settings (Wood, 1980a; Connor et al., 2000; Rapprich et al., 2007; Valentine and Gregg, 2008). The primary aim of morphometric studies on volcanoes (mostly on scoria cones) is to establish slope angle values, which are important parameters for assessing the relative age of volcanic cone within a monogenetic volcanic field (e.g. Wood, 1980a). A fresh scoria cone has been said to have initial slope angle values between 30–33° (Wood, 1980b; Riedel et al., 2003), with these values decreasing systematically during the course of degradation (Wood, 1980a; Dohrenwend et al., 1986; Hooper, 1995). During cone formation and subsequent degradation, various processes can shape the morphology of volcanic edifices (Wood, 1980a; Rodriguez-Gonzalez et al., 2011; Büchner and Tietz, 2012; Kereszturi and Németh, 2012). The syneruptive controlling parameters determine the initial geometry and properties of pyroclastic deposits. These processes include, for example, changing magma fragmentation style, migration or changing dimensions of a feeder-dyke beneath the edifice, effusive activity or cone collapses and/or breaching due to intermittent explosions (Corazzato and Tibaldi, 2006; Martin and Németh, 2006; Kereszturi et al., 2011; Martí et al., 2011; Németh et al., 2011; Starkova et al., 2011), all of which can lead to the formation of complex volcanic landforms in terms of inner architecture, pyroclastic deposits types and morphometry. Such diversity of morphology and architecture is a source of pitfalls for morphometric parameterization and morphometry-based dating. On the other hand, the post-eruptive, erosional processes such as linear dissection of the flanks, landslides or sediment creep, also play vital roles in shaping of volcanic landforms after the cessation of volcanic activity (Hooper and Sheridan, 1998). A number of both syn- and post-eruptive controlling processes make the interpretation of morphometry of scoria cones more complicated than it has been assumed by previous studies (Wood, 1980a; Hooper and Sheridan, 1998). In early studies, the initial geometrics of volcanic edifices were assumed to be similar, providing a basis for comparative morphometric studies (Settle, 1979; Wood, 1980a). In other words, previous studies interpreted the present morphometric characteristics entirely as the result of erosional processes governed by climatic conditions, assuming homogenous inner architecture and similar initial geometry (Porter, 1972; Wood, 1980a; Hooper, 1995; Hooper and Sheridan, 1998; Pelletier and Cline, 2007). In order to test the variability of slope angle values in relation to syn- and post-eruptive controlling factors, nine young (≤Pleistocene) scoria cones in Tenerife, Canary Islands are parameterized morphometrically. Scoria cones on volcanic islands such as Tenerife (Fig. 1) are located along volcanic rift zones in extensional stress fields (Carracedo et al., 2007; Geyer and Martí, 2010). The nine studied scoria cones were selected on the basis of their known young (≤Pleistocene) ages (Carracedo et al., 2007) and their diverse pre-eruptive surface inclinations. As a consequence of the young age, the morphology of the studied cones has not significantly been modified by erosional processes as confirmed by the lack of vegetation or gullies (see for example Figs 5–7). Thus, the slope angles measured on the outer flanks of a scoria cone can be parameterized by using high-resolution Digital Elevation Models (DEMs), allowing quantification of morphometric variability among monogenetic edifices. These young cones with limited erosional modification provide good opportunity to test the uniformity of initial geometry, one of the assumptions of morphometry-based dating and comparative studies on scoria cones (Porter, 1972; Wood, 1980a; Hooper and Sheridan, 1998).
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Geological settings The Canary Archipelago is located a few hundred of kilometres from the NW coast of Africa. Of the seven volcanic islands forming the Canarian Archipelago, Tenerife is the largest (2,034 km2) and highest (3,718 m asl). The first shield stage eruptive products of Tenerife (Fig. 1) are exposed as old volcanic massifs, e.g. Teno, Anaga or the Roque del Conde formed between 12 Ma and 3.5 Ma (Ancochea et al., 1990; Thirlwall et al., 2000). The new phase of volcanism built up a large volcanic complex sitting on top of older remnants (Fig. 1), which was merged and partially covered by the eruption products of the Las Cañadas volcano (Ancochea et al., 1990; Carracedo, 1994; Carracedo et al., 2007). The Las Cañadas volcano has been truncated by (1) lateral gravitational collapses (Carracedo et al., 2011) or by (2) multiple, vertical collapses following emptying of the shallow magma chamber (Marti and Gudmundsson, 2000). Other important volcanic structures are the central edifice (Teide–Pico Viejo volcano) and its associated rift zones (Fig. 1) originating either from (1) swelling of the surface due to mantle ascent (Carracedo, 1994; Carracedo et al., 2007) or from (2) spreading of the upper volcanic structure (Walter, 2003). Recent volcanic activity and possible hazard are most likely linked to these rift systems, which host the majority of the subaerial monogenetic volcanoes studied in this paper (Carracedo et al., 2007; Doniz et al., 2008; Geyer and Martí, 2010).
Fig. 1: Simplified geological map of the island of Tenerife including the major shield edifices in the three corners of the present island, the deposits of Las Cañadas volcano and the location of the most recent products of Pico-Viejo stratocone and its rift zones based on Ancochea et al. (1990), IGME (2003) and Carracedo et al. (2007). Note: STR – Santiago del Teide rift, DR – Dorsal Rift, SVZ – Southern Volcanic Zone.
Materials and methods Digital elevation models (DEMs) were created from the 5 m interval contour lines of the 1:5,000 Tenerife topographic map sheets (GRAFCAN, 2009). A linear interpolation method specifically designed for contours was implemented with the ILWIS raster GIS software (Gorte and Koolhoven, 1990). Linear interpolation is an exact interpolation method because it fits to the input data, i.e. contour lines (Gorte and Koolhoven, 1990). This method rasterizes the digitized vector contour lines first with the contour elevation values, then the unknown elevation values are interpolated. The interpolation is performed between the two nearest contour lines by using the shortest distances measured both forwards and backwards directions on the rasterized maps (Borgefors, 1984; Gorte and Koolhoven, 1990). Selection of proper cell size is, however, crucial because large cells containing two or more contour lines cannot resolve the original detailed topographic information. This loss of resolution and thus morphologic
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information is particularly likely on steep slopes with close contour line spacing. In order to retain the maximum morphological information carried by the contour lines the appropriate grid cell size resolving all individual contours was determined by a trial-and-error approach of rasterizing the contours to 0.5 m, 1 m and 2 m cell sizes. The cell size was regarded fine enough if the rasterized contour lines were separated by at least one undefined cell width. This was numerically tested by applying a simple neighbourhood operation in a 3 3 moving window. If none of the contour line raster cells in the map have neighbour cells with a different elevation value, then the tested grid cell size was defined as the right resolution for DEM interpolation. In this case, the 0.5 0.5 m grid cell size was found to properly resolve and represent the original contour line information, so the final DEM was interpolated from the contours to the 0.5 m grid cell size. In order to improve slope gradient calculation, the DEMs were smoothed with 5 5 (2.5 2.5 m) moving average window (see Electronic Supplementary Material 1). A limitation of linear interpolation is that it creates flat areas within closed contour lines at hill tops and natural depressions, with cells of constant elevation value. This systematic error can affect morphometric calculations such as slope statistics. In order to improve statistical analyses topographic peaks within closed contour lines were not considered in further morphometric calculations, including slope angle statistics. These minor peaks are located around the crater rim, which anyway tends to be degraded early (Pelletier and Cline, 2007; Valentine et al., 2007).
Fig. 2: (A) Change of slope angles (Smean, Smedian and Smode) as a function of grid cell size examined on the outer flanks of Fasnia scoria cone from Tenerife. (B) The slope angle histogram for the same cone showing the unimodal distribution of slope values for grid cell size of 0.5 m, which is essential for accurate univariate analysis. The DEM‘s accuracy was characterized by the root mean square error (RMSE) (Fisher and Tate, 2006) comparing the interpolated DEM elevation to independent spot heights digitalized from the topographic maps:
RMSE =
( Z DEM
Z ref ) 2
(1)
n
where ZDEM is grid cell elevation, Zref is the reference spot height elevation and n is the number of reference points. In the case of the studied DEM, the RMSE was calculated separately for each studied volcanic cone and it ranged from ±0.5 m to ±3.8 m (see Electronic Supplementary Material 1). This is well within the original 5 m contour interval, confirming the appropriateness of the interpolation method. The gradient vector of a digital surface is characterized by it length, i.e. the slope (S) and a direction, i.e. aspect (A). These properties were calculated as
S = arctan
fx 2
fy 2
A = 180° – arctan(fy/fx) + 90°(fx/|fx|)
(2) (3)
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where A is the modified directional component of the gradient vector pointing in the down flow direction and measured clockwise from north. The partial derivatives (fx, fy) were estimated using the unweighted eight-point Prewitt operators: fx = (Z3+Z6+Z9-Z1-Z4-Z7)/6ΔX and fy = (Z1+Z2+Z3-Z7-Z8-Z9)/6ΔY in a 3 3 moving window (Jordan, 2007). Besides its smoothing effect, this method has the advantage of being identical to a least-squares plane fit to the 9 window elevations (Sharpnack and Akin, 1969), thus the linear Prewitt operators are particularly suitable for linearly interpolated surfaces. The slope and aspect values of a DEM are highly dependent on the resolution used (Zhou and Liu, 2004; Deng et al., 2007; Dragut et al., 2011). In order to visualize changes of slope angle as a function of grid cell size, a series of DEMs were generated from the same contour lines in different resolutions from 0.2 m to 20 m (Fig. 2A). The slope angles were calculated for only the outer flanks of Fasnia edifice where central tendency of slope angles is expected (Fig. 2B). The Smean and Smedian values showed a sharp decrease in their values around 5 m resolution (Fig. 2), while the S mode showed no trend due to the multimodal slope angle histogram.
Fig. 3: Establishing the basal inclination by a first-order trend surface interpolated using the least-squares method and spot height data. Example is the Arafo scoria cone. (A) View of the volcanic edifice and its surrounding on an
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orthophotograph draped on the DEM. (B and C) Fitted first-order trend surface through the spot heights (red points) with the location of the outer flanks. The interpolated trend surface displays the general slope and aspect of the preeruptive surface. The pre-eruptive surface or basement slope (Sbasal) and aspect (Abasal) were also calculated (Fig. 3). This preeruptive surface of the studied cones was modelled by a first-order trend surface, i.e. plane, fitted by the least-squares method to the digitalized spot heights (de Smith et al., 2009). To obtain the pre-eruptive surface, only those spot heights were used which were not located within the area of (1) the tephra blanket around the cone, (2) the cones‘ slope, (3) the associated lava flow fields, and (4) the large valleys located near the analysed cones. Orthophotos, geological maps and field observations were used to delineate these areas. Morphometric parameters and geometry of monogenetic volcanoes, including slope angles on the outer flanks, can vary because of the pre-eruptive surface inclination (Tibaldi, 1995; Kervyn et al., 2012). In the present study, the volcano outer flanks were classified into three types in relation to the slope of the underlying pre-eruptive basal surface. With this classification, inner intra-flank variability of slope angle is detected. These flank sectors are called uphill (Fuphill), downhill (Fdownhill) and other (Fother) and were defined as (see in the Fig. 4): Fdownhill = Abasal ±45° Fuphill = Abasal +180 ±45°
(4) (5)
Fig. 4: (A) Aspect-based flank segment delimitation method developed for scoria cones in Tenerife demonstrated using the Arafo scoria cone as an example. Note that the white parts of the classified aspect map are flat (i.e. zero slope) areas resulting from the linear interpolation method. These parts were discarded from the slope angle
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calculations. Inset diagram shows the graphical definition of flank sectors. (B) Local slope angle statistics for the Arafo scoria cone. Thus, the Fuphill and Fdownhill slope facets are perpendicular (±45°), while the Fother are orthogonal (±45°) to the dominant pre-eruptive surface inclination. Scoria cones are mostly built up from loose, scoriaceous lapilli fragments (Riedel et al., 2003). If the fragment-size is in a narrow range for a pristine scoria cone (Wood, 1980b) only unimodal distribution of slope angles are expected. Thus central tendency statistic of average (S mean), median (Smedian) and mode (Smode) were used for the flank segments of each studied edifice. To identify inappropriate statistical slope angle descriptors, slope angle histograms were calculated and presented for each studied scoria cone. The calculated slope angle values were also visualized as a function of slope aspect in the polar plots in order to detect geographical location of variance in slope angles on the outer flanks. The outer flanks were defined as the surface between slopebreak at the foot of the cone and the crater rim. In the delimitation of the outer flanks, 1:30,000 aerial photographs (with 40–50 cm resolutions), 1:25,000 geological maps (IGME, 2003) and field observations were used. Results Out of nine examined young scoria cones from Tenerife only three examples are described in this section in terms of location, volcanology, morphology and slope angle characteristics for demonstration purposes. These three examples represent a wide spectrum of pre-eruptive inclinations from 4° to 11°. The rest of the studied scoria cones with detailed description and additional figures can be found in the Electronic Supplementary Material 2.
Fig. 5: Overview map of Montaña Arafo (left) with topographic profiles (insets profiles) along (A-A‘ profile) and perpendicular (B-B‘ profile) to the major axis of pre-eruptive surface slope. The white arrow shows the location of deepest point of the crater. Note that the contour interval is 5 m. Slope angle histograms (right) for the uphill, downhill and other flank sectors with the major descriptive statistics.
Montaña Arafo The Arafo scoria cone (Fig. 1) is located on the floor of a large valley at the NE rift zone on the southern slopes of Tenerife. It is also a young volcanic vent formed in 1705 AD and it is associated with the Sietefuentes, Fasnia and Arafo triple eruptions (Carracedo et al., 2007). The pyroclastic edifice is built up by scoriaceous lapilli
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and ash beds reflecting more explosive than effusive behaviour. The scoria cone is horseshoe-shaped due to crater breaching (Fig. 5). The scoria cone of Arafo is in a special location in a valley, where the valley floor (pre-eruptive surface) has an 11° slope angle. The direction of this interpolated surface is facing toward SE (129°; Table 1). The slope angles are generally the steepest among the cones of Tenerife according to our DEM-based calculations. The uphill (Smean = 32°, Smedian = 32°, Smode = 33°) and other (Smean = 31°, Smedian = 31°, Smode = 32°) flank sectors are steeper than downhill sector (Smean = 27°, Smedian = 27°, Smode = 22°, Table 1). The slope standard deviations are relatively low, between 3° and 5° and have the lowest values in the Fuphill, increasing towards Fdownhill (Table 1). The slope angle histograms show skewed and bimodal distribution, except the F other, making accurate capture of descriptive statistics harder (Fig. 5).
Fig. 6: Montaña Boca Cangrejo. For details see Fig. 5 caption.
Montaña Boca Cangrejo The eruptions of Boca Cangrejo (Fig. 1) took place on the centre of the NW rift zone in 1492 AD based on historical descriptions (Romero, 1991; Carracedo et al., 2006). The historic documentation is also supported by recent radiocarbon age determinations providing an age range of 1440 and 1660 AD for the cone's activity (Carracedo et al., 2007). The eruption of Boca Cangrejo scoria cone includes cone-emplacement as well as emission of an extended aa, pahoehoe and block lava flow field that covers a large part of the island (8 km 2) on the southern part of STR with a length of about 10 km. The Boca Cangrejo scoria cone consists of successive beds of lava spatter, scoriaceous lapilli and ash deposits. This volcanic complex has a multiple vent system with at least 3 larger, wellpreserved craters (Fig. 6). Two of these craters are ring-like explosion craters and three are breached probably due to the high effusive activity in the waning stage of the volcanic edifice construction (Dóniz, 2009). The Boca Cangrejo is situated on a gentle pre-eruptive surface with an inclination of 7°. The cone is facing west (aspect direction of underlying surface is 288°; Table 1). The upper slope sector has relatively low proportion of pixels (5% from the total number of slope pixels), but it shows nearly the same results as the rest of the cone flanks (Table 1). Based on the slope angle histograms, the Boca Cangrejo scoria cone is one of the most complex in terms of morphometry because of the multimodal and skewed distribution of the slope histogram (Fig. 6). This asymmetry of slope histograms is also represented by the large standard deviation around 7° and 9° and the scattered values of slope angle parameters measured on the other (Smean = 26°, Smedian = 27°, Smode = 29°) and downhill (Smean = 22°, Smedian = 23°, Smode = 27°) flank segments (Table 1).
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Montaña Fasnia Montaña Fasnia (Figs 1) is located on the south edge of the NE rift and formed in 1705 AD (Carracedo et al., 2007). It comprises two well-distinguished, highly asymmetrical cone-like landforms which were probably breached by extensive effusive activity. This edifice associated with a fissure eruption has a highly elongated profile with the dimensions of 200 m width and 1200 m length (Fig. 7) with multiple craters. The edifice is built up by mostly lapilli and bombs and spatter-dominated beds. The aa lava field associated to the edifice covers an area of 0.52 km 2 (Dóniz, 2009). Fasnia cones are a significantly breached from the south and the substrate dips toward 142° (SE direction) with a relatively low basal slope angle (4°; Table 1). The slope angle variations among the flank sectors are relatively low. All of the calculated slope angles are within the range of 28° to 31° with standard deviation between 3° and 4° (Fig. 7). All of the slope histograms show distinct unimodal behaviour, however some skewed distribution can be found in the cases of Fother and Fdownhill flank sectors (Fig. 7).
Fig. 7: Montaña Fasnia. For details see Fig. 5 caption.
Discussion Evidence of morphometric variability All of the studied scoria cones are less than a few thousand years old (Carracedo et al., 2007; Doniz et al., 2008). Consequently, their morphometric characteristics such as slope angle should be ≥30° according to previous observations for fresh and pristine scoria cones, e.g. the Merriam age group is characterized by 30.8±3.9° from the San Francisco Volcanic Field, Arizona (Wood, 1980a; Hooper and Sheridan, 1998). In contrast to this expected high value, the slope angles of the studied cones vary from 22° to 30° for S mean and from 21° to 30° for Smedian measured as an average of flank sector values. Individual flank sectors are in the same range (Table 1). The S mode values are not presented here because of their high variability (see Fig. 2). This variance in slope angles of young scoria cones on Tenerife is unexpected. Based on the young examples, the morphometric variability exists: (1) among the volcanic edifices, i.e. the slopes of young cones are not always in the same range and they do not always have the expected slope ≥30°, and (2) within a single edifice, i.e. there are differences between the dominant values of various flank sectors.
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Morphometric variability among the volcanic edifices has an important consequence for morphometric analysis because a narrow variability of slope angle and initially similar geometries are the basis of the comparative morphometric studies, including morphometry-based dating (Settle, 1979; Conway et al., 1998; Sucipta et al., 2006), or erosional studies on volcanoes (Wood, 1980a; Bemis et al., 2011; Inbar et al., 2011; Fornaciai et al., 2012). This key assumption is not, however, supported by this study of young scoria cones from Tenerife. This is in agreement with recent studies indicating inaccuracies in morphometric-based dating (Kereszturi and Németh, 2012). Similar variances have been documented for cones that have not reached their final, well-developed size and geometry (Bemis et al., 2011; Kervyn et al., 2012) and/or collapsed or were truncated during eruption (Kereszturi and Németh, 2011; Németh et al., 2011).
Fig.8: Slope angles as a function of slope aspect visualized in a polar plot (black dots). Red arrows display the overall dip direction of the pre-eruptive topography. Black curves with small arrows in the polar plots show the approximate location of lava outflows from fissures during the evolution of each studied scoria cone. The solid and dashed red circle are equivalent to the generally used 30.8° slope angle and its error range of ±3.9°, respectively, expected for young volcanic edifices according to Wood (1980a). Slope dots inside and outside the dashed red circles represent morphometric variability from the expected values for a fresh scoria cone.
Fine-scale morphometric variability among flank segments within a single edifice is also documented by this study. These segments corresponding to flank sectors along and perpendicular (±45°) to the main axis of terrain slope (±45°), and show flank-slope differences of as much as 12° (Fig. 8), which is about 1/3 of the entire range of natural spectrum of angles of repose of loose, granular scoriaceous volcano flanks (Wood, 1980b; Riedel et al., 2003). To
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detect and visualize such changes as a function of position within individual edifices, polar plots were made (Fig. 8), with emphasis on the location of the expected ‗average‘ values, i.e. 30.8±3.9° (Wood, 1980a). The expected average slope angle is fulfilled by the Fuphill segment of the Arafo scoria cone (Figs 5 and 8). This flank segment has a low standard deviation (3°) and is in the expected ≥30° range. The overall geomorphic state of Arafo scoria cone is interesting because there is an increase in the standard deviation towards the Fdownhill sector, from 3° to 5° (Fig. 8). The observed increasing slope segment variability results from the combination of inclined basement and the effusive activity and/or flank collapse (Figs 5 and 8). Origin of morphometric variability The morphology of scoria cones can change rapidly (years to decades) after eruption (Inbar et al., 1994; Fornaciai et al., 2010; Inbar et al., 2011). Nevertheless, these secondary modifications including deflation by wind, small gravitational landslides or rain splash erosion (Wood, 1980a; Hooper, 1999) on the flank of a young volcanic edifice (≤ka) do not extremely alter the original morphology (Pelletier and Cline, 2007; Fornaciai et al., 2010). The morphometric variability detected among these young cones through slope angle values resulted from syn-eruptive rather than post-eruptive processes. Such morphometric variability may be related to either non-volcanic and/or volcanic processes including (1) pre-eruptive surface inclination, (2) vent migration and associated crater breaching, (3) effusive activity and associated crater breaching and flank collapses as well as (4) variation of the properties of the pyroclastic successions, e.g. grain size, degree of welding and agglutination. From these controlling factors on initial cone morphology, the effects of pre-eruptive surface inclination and of effusive activity are hardly distinguishable from each other because most of the lava flows left the cones at the base of their downhill flank (Fig. 8). These lava outflows and associated processes such as flank collapses (Holm, 1987; Németh et al., 2011) may have affected the final morphometry of the studied volcanic edifices by partially removing, rotating and gradually distorting the flank segment(s), as on the Arafo scoria cone (Figs 5 and 8). Flank collapses and subsequent rebuilding of cones represent a more complex eruption history than may be typical for pure symmetric cones (Holm, 1987). The pre-eruptive surface inclination helps to develop such collapse and breaching, as indicated here by the preferred extrusion of lavas from the cones' downhill flanks (Fig. 8). A larger degree of morphometric variability can be expected with pre-eruption topographic slopes exceeding 5° (Table 1) which is in agreement with the field-based observation at the Los Morados scoria cone in Argentina (Németh et al., 2011) and with the LiDAR-based characterization of parasitic cones from the flank of Mt. Etna (Favalli et al., 2009). Importance of morphometric variability The abovementioned syn-eruptive processes lead to morphometric variability both among individual volcanic edifices and between individual flank segments within the same edifice. Such initial morphometric variability has important implications for interpretation of morphometric characteristics of volcanic edifices, cluster of cones or even volcanic fields. Because there is morphometric even among young, uneroded scoria cones, edifice ages and their general implications for eruption histories of individual edifices or groups cannot be inferred. Comparison should be restricted to edifices with strict age-control, knowledge on eruption history and pyroclastic composition as well as information on the initial geometry of the edifice. The studied cones were sorted in decreasing order of slope angles of the three flank sectors with the Fasnia or Arafo cones having the highest slopes. These steep cone flanks would be traditionally interpreted as a sign of young age, but they are not the youngest edifices (Table 1). More interesting is that the pre-Holocene cone of Güímar has higher flank slopes (26–28°) than the 600 and 300 years old edifices including Boca Cangrejo (22–25°) or Garachico (22– 28°) (Table 1). Similarly, the morphometric signature of Güímar and Chinyero scoria cones are in the same range between 29° and 26° in spite of their age difference of over 10,000 years (Table 1). These observations show that the same morphological state of an edifice can be reached either during eruption or as a consequence of post-eruptive processes. In this case, the 29° and 26° slopes for Güímar reflect a slight modification by erosional processes (e.g. weathering and soil-formation), while the fresh (100 years old) Chinyero is formed by syn-eruptive processes, and shows no evidence of weathering or soil-formation. A key inference from our work is that comparative morphometric investigation of monogenetic volcanoes without knowledge of the initial geometry cannot be used to infer relative ages of well-preserved cones. These distorting effects of the initial geometry fade away by the final stages of the erosion, when more compact and erosion-resistant layers become exposed on the flanks of a scoria cone (Kereszturi and Németh, 2012), but this usually requires million years (Wood, 1980a; Kereszturi and Németh, 2012), or in some cases, as long as 40 My (Rapprich et al., 2007; Büchner and Tietz, 2012). Relation of morphometric variability with basement inclination An increasing difference can be identified among the three overall slope descriptors (S mean, Smedian and Smode; Fig. 9), which is related to the occurrence of multimodal and skewed slope angle histograms (see Figs 5–7 and Electronic Supplementary Material 2). These differences coincide with the overall inclination of the pre-eruptive
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surface, and it is characterized by a moderate positive, Pearson correlation with correlation coefficients of 0.61 for Smean, 0.67 for Smed and 0.97 for Smode. These values were calculated without Mt. Chio and Mt. Chahora due to their missing uphill slopes. If Mt. Chio and Mt. Chahora were included, the correlation coefficient between the maximum slope angle difference between flank segments and the pre-eruptive inclination is ≥0.90. The largest difference in slope angles between flank segments as a function of pre-eruptive inclination, three groups were recognized (Fig. 9). The analysed volcanic edifices in the present study are located on a pre-eruptive surface with inclination of 0–5° (‗plain‘), 5–10° (‗gentle‘) and over 10° (‗steep‘).
Fig. 9: Graph showing the maximum morphometric variability between slope angles derived from flank segments of scoria cones as a function of pre-eruptive surface inclination. See the text for detailed explanation.
The scoria cones located on plain, sub-horizontal pre-eruptive surfaces (up to 5°) have the lowest differences between Fuphill, Fdownhill and Fother sectors in the mean, median and mode slope angle values (Fig. 9). The largest differences among slope angle parameters are usually less than 3° (Table 1). Examples of this type of cone are the Montaña Güímar, Fasnia and Chinyero. This similarity observed in the slope angles of flanks can be a result of (1) the almost plain-like pre-eruptive terrain and/or (2) the homogenous distribution of pyroclasts in certain slope sectors. The homogenous distribution of pyroclasts can also be the result of a horizontal pre-eruptive surface. For example, cones formed on a horizontal pre-eruptive surface are less likely to have slope collapse and/or breaching when compared to those that erupted onto a pre-eruptive surface with high basal inclinations exceeding 4° (Németh et al., 2011). Sub-horizontal pre-eruptive topography helps the formation of a well-developed edifice with symmetrical cone geometry, though it may still be modified by wind, vent migration and/or lava outflow and
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associated breaching. This finding is in agreement with experimental modelling results (Tibaldi, 1995; Kervyn et al., 2012). The scoria cones built on gently sloping pre-eruptive surfaces with inclinations of 5°–10° are characterized by greater variation of slope angle differences between flank segments, from 3°–9° (Fig. 9 and Table 1). Three studied cones are of this type, the Garachico, Reventada and Boca Cangrejo scoria cones. These differences are high enough (e.g. exceeds the overall accuracy of the input topographic data) to cause problems for morphometry-based dating, and comparative studies of scoria cone degradation. The scoria cones situated on pre-eruptive surfaces with inclinations of ≥10° are represented by Chahorra, Chío and Arafo scoria cones. These examples formed on 24°, 14° and 11° pre-eruptive surfaces, respectively (Fig. 9). In this group, two of the studied edifices have no uphill facing flanks. All of these examples have breached crater morphology, where the direction of breaching is in accordance with the direction of inclination. The difference between slope sectors is the largest for the Chahorra cones, and ranges up to 28° due to the missing uphill flanks (Table 1). In addition to the missing uphill facing slopes, the extremely elongated morphology of Chío scoria cone may also be related to (1) the high degree of pre-eruptive surface inclination, (2) formation of fissure rather than a ‗point-like‘, well-localized vent, and/or (3) late-stage effusive activity. Conclusions The nine studied young cones in Tenerife are characterized by wide ranges of slope angles for individual edifices and for individual flank sectors making morphometric parameters unique for every cone studied. Such variation in slope angle values could be as high as 12°, which is significantly higher than indicated early studies (Porter, 1972; Wood, 1980a). Due to the known young geological age (mostly Holocene), the observed morphometric variability can be interpreted as the result of mostly syn-eruptive processes such as (1) pre-eruptive surface inclination, (2) vent migration, (3) lava outflows and associated crater breaching and (4) differences in the properties of pyroclastic rocks preserved in the flanks of the volcano. The studied young cones are seen to have variations in slope angles of certain flank segments when the preeruptive inclination gets steeper. The observed morphometric variability may become significant on cones on basal slopes ≥5°, as suggested by recent studies (e.g. Németh et al., 2011; Kervyn et al., 2012). This shows that the basement inclination is an important factor in triggering flank collapses and subsequent re-construction processes, leading to complex eruption histories and often complex geomorphology of the resultant volcanic edifice. This diverse nature of edifice growth possibly make the internal architecture of a scoria cone complicated, which plays important the role in the subsequent degradation. The observed wide range of morphometric variability caused by syn-eruptive processes raises the question about the interpretation of morphometric parameters. Previous studies interpreted morphometric parameters of monogenetic volcanic edifices in two ways: (1) primary, geometric modifications triggered by volcanological processes (Tibaldi, 1995; Corazzato and Tibaldi, 2006; Doniz et al., 2008; Bemis et al., 2011; Fornaciai et al., 2012; Kervyn et al., 2012), and (2) secondary, post-eruptive surface modifications caused by erosional-processes during the degradation (Wood, 1980a; Hasenaka and Carmichael, 1985; Dohrenwend et al., 1986; Hooper, 1995; Hooper and Sheridan, 1998; Inbar and Risso, 2001; Sucipta et al., 2006; Favalli et al., 2009; Fornaciai et al., 2010; NegreteAranda et al., 2010; Rodríguez et al., 2010; Inbar et al., 2011; Rodriguez-Gonzalez et al., 2011; Kereszturi and Németh, 2012). However, morphometric characteristics as documented here are too complex to interpret in a single way because they could bear both primary (i.e. results of syn-eruptive processes) and secondary (i.e. results of erosion-related processes) information. Theoretically, the likelihood of syn-eruptive process shaped morphometric values is higher in the first stage of the degradation history than after a few ka or even Ma after the eruptions ceased. Further studies should target the understanding of the meaning of morphometric parameters at certain stages of erosion. It seems that using large number of scoria cones of varying age is inappropriate for detailed geomorphic studies. Without strict age control, simple calculations of slope angles can merge the effect of various geological/volcanological and erosion processes which in turn can lead morphometric misinterpretation. Thus, the simple global interpretation of morphometric characteristics based on large number of scoria cones should be avoided. The presented methods are suitable to detect morphometric irregularities found on the flanks of monogenetic scoria cones. In addition to the flank sector analysis, slope angle histograms proved to be useful for controlling the accuracy of statistical estimates. Also, polar plots efficiently describe the morphometric variability of small-volume, monogenetic volcano flanks. In this study, flank sectors located parallel to the main direction of the pre-eruptive basal surface have multi-modal and asymmetric slope distributions suggesting a control of basal tilt. The combination of such techniques allows a more detailed investigation of the late-stage, syn-eruptive morphometric evolution of young scoria cones. Acknowledgements Gabor Kereszturi would like to thank the PhD Research Fellowship offered by Volcanic Risk Solutions, Institute of Natural Resources at the Massey University (New Zealand). This research was also partly supported by Department
12
of Geology and Mineral Deposits, University of Miskolc, Hungary. Authors are grateful for the topographic maps and orthophotos to the Gobierno de Canarias (GRAFCAN). The comments and discussion with Mike Tuohy and Matthew Irwin (Massey University) and the comments by the Editors, Benjamin van wyk de Vries and James White, as well as the two anonymous Journal Reviewers improved the quality of the manuscript.
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northern Baja California, Mexico: Tectonics and volcanism of San Borja volcanic field. J Volcanol Geotherm Res 192:97-115 Németh K, Risso C, Nullo F, Kereszturi G (2011) The role of collapsing and rafting of scoria cones on eruption style changes and final cone morphology: Los Morados scoria cone, Mendoza, Argentina. Central European Journal of Geosciences 3(2):102-118 Pelletier JD, Cline ML (2007) Nonlinear slope-dependent sediment transport in cinder cone evolution. Geology 35(12):1067-1070 Porter SC (1972) Distribution, Morphology, and Size Frequency of Cinder Cones on Mauna Kea Volcano, Hawaii. Geol Soc Am Bull 83(12):3607-3612 Rapprich V, Cajz V, Kostak M, Pécskay Z, Ridkosil T, Raska P, Radon M (2007) Reconstruction of eroded monogenetic Strombolian cones of Miocene age: A case study on character of volcanic activity of the Jicin Volcanic Field (NE Bohemia) and subsequent erosional rates estimation. Journal of Geoscience 52(3-4):169-180 Riedel C, Ernst GGJ, Riley M (2003) Controls on the growth and geometry of pyroclastic constructs. J Volcanol Geotherm Res 127(1-2):121-152 Rodriguez-Gonzalez A, Fernandez-Turiel JL, Perez-Torrado FJ, Aulinas M, Carracedo JC, Gimeno D, Guillou H, Paris R (2011) GIS methods applied to the degradation of monogenetic volcanic fields: A case study of the Holocene volcanism of Gran Canaria (Canary Islands, Spain). Geomorphology 134(3-4):249-259 Rodriguez-Gonzalez A, Fernandez-Turiel JL, Perez-Torrado FJ, Paris R, Gimeno D, Carracedo JC, Aulinas M (2012) Factors controlling the morphology of monogenetic basaltic volcanoes: The Holocene volcanism of Gran Canaria (Canary Islands, Spain). Geomorphology 136(1):31-44 Rodríguez SR, Morales-Barrera W, Layer P, González-Mercado E (2010) A quaternary monogenetic volcanic field in the Xalapa region, eastern Trans-Mexican volcanic belt: Geology, distribution and morphology of the volcanic vents. J Volcanol Geotherm Res 197(1-4):149-166 Romero C (1991) Las manifestaciones volcánicas históricas del Archipiélago Canario. Consejería de Política Territorial. Gobierno Autónomo de Canarias, Santa Cruz de Tenerife, Spain Settle M (1979) The structure and emplacement of cinder cone fields. Am J Sci 279(10):1089-1107 Sharpnack DA, Akin G (1969) An algorithm for computing slope and aspect from elevation. Photogrammetric Survey 35:247-248 Starkova M, Rapprich V, Breitkreuz C (2011) Variable eruptive styles in an ancient monogenetic volcanic field: examples from the Permian Levín Volcanic Field (Krkonoše Piedmont Basin, Bohemian Massif). J Geosci 56:163180 Sucipta IGBE, Takashima I, Muraoka H (2006) Morphometric age and petrological characteristic of volcanic rocks from the Bajawa cinder cone complex, Flores, Indonesia. J Mineral Petrol Sci 101(2):48-68 Thirlwall MF, Singer BS, Marriner GF (2000) 39Ar–40Ar ages and geochemistry of the basaltic shield stage of Tenerife, Canary Islands, Spain. J Volcanol Geotherm Res 103(1-4):247-297 Tibaldi A (1995) Morphology of pyroclastic cones and tectonics. J Geophys Res 100(B12):24521-24535 Valentine GA, Gregg TKP (2008) Continental basaltic volcanoes - Processes and problems. J Volcanol Geotherm Res 177(4):857-873 Valentine GA, Krier DJ, Perry FV, Heiken G (2007) Eruptive and geomorphic processes at the Lathrop Wells scoria cone volcano. J Volcanol Geotherm Res 161(1-2):57-80 Walter TR (2003) Buttressing and fractional spreading of Tenerife, an experimental approach on the formation of rift zones. Geophys Res Lett 30(6):1296 Wood CA (1980) Morphometric analysis of cinder cone degradation. J Volcanol Geotherm Res 8(2-4):137-160 Wood CA (1980) Morphometric evolution of cinder cones. J Volcanol Geotherm Res 7(3-4):387-413 Zhou Q, Liu X (2004) Analysis of errors of derived slope and aspect related to DEM data properties Comput Geosci 30(4):369-378
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Table 1: Results of the aspect-based flank sector delimitation of studied locations from Tenerife. Abbreviations: * – no representative proportion of pixel numbers (under 5% of the total population of pixels); ** –largest difference between flank segment slope angle values. All values are in degrees, except the number of cells. Slope aspect (degree) Edifice
Age
Fdownhill
Slope angle (degree) Fuphill
Fuphill
basal
Fother
Fdownhill
Fwhole
Difference
basal min
max
min
max
Smean
Smed
Smode
N of cells
Smean
Smed
Smode
N of cells
Smean
Smed
Smode
N of cells
Smean
Smed
Smode
N of cells
Smean
Smed
Smode
Chahorra
1798 AD
232
7
97
187
277
24
0.0*
0.0*
0.0*
0.0 (0.0%)*
28
29
29
55,323 (32.2%)
26
26
29
116,758 (67.8%)
27
27
29
172,081 (100%)
28
29
29
Chío
3933±212 yr BP
283
58
148
238
328
14
29*
29*
29*
598 (0.2%)*
23
23
19
184,081 (68%)
21
19
15
85,973 (31.8%)
22
22
19
270,652 (100%)
8
10
14
Arafo
1705 AD
129
264
354
84
174
11
32
32
33
99,485 (22.6%)
31
31
32
231,432 (52.6%)
27
27
22
108,993 (24.8%)
30
31
32
439,910 (100%)
5
5
11
Boca Cangrejo
1492 AD
288
63
153
243
333
7
25*
25*
20*
12,242 (4.8%)*
26
27
29
170,785 (67.1%)
22
23
27
71,380 (28.1%)
25
26
27
254,412 (100%)
3
4
9
Garachico
1706 AD
13
148
238
328
58
7
29
29
30
187,272 (50.9%)
24
24
25
84,964 (23.1%)
22
23
23
95,953 (26.0%)
26
27
27
359,316 (100%)
7
6
7
Reventada
895±115 yr BP
290
65
155
245
335
6
22
22
19
44,448 (9.9%)
26
27
27
345,244 (76.9%)
21
21
19
59,266 (13.2%)
25
25
27
448,958 (100%)
5
6
8
Fasnia
1705 AD
142
277
7
97
187
4
31
31
31
62,430 (62.4%)
30
30
29
18,537 (18.5%)
30
30
28
19,166 (19.1%)
30
30
31
100,133 (100%)
1
1
3
Chinyero
1910 AD
317
92
182
272
2
3
29
28
27
38,885 (19.8%)
27
27
24
108,721 (55.5%)
26
26
27
48,415 (24.7%)
27
27
27
195,821 (100%)
3
2
3
Güímar
preHolocene
115
250
330
70
160
1
28
29
31
429,473 (31.1%)
27
28
30
656,889 (47.6%)
26
27
29
294,106 (21.3%)
28
28
28
1,380,468 (100%)
2
2
2
AVE
28.5
28.7
28.3
26.8
27.2
27.1
24.5
24.6
24.3
26.7
27.0
27.3
STD
3.27
3.39
5.12
2.69
2.74
3.99
3.09
3.33
5.1
2.63
2.81
3.79
16
Electronic Supplementary Material 1: Table showing the properties and accuracy of the DEMs for the nine studies scoria cones in Tenerife. Note that the n is the number of pixels.
Touching pixels Scoria cone
total map area 1m
outer flanks
0.5 m
Error descriptors
Flat pixel analysis total map area real flat
inflow
outer flanks outflow
n
%
n
%
2 m
Chahorra
588
0.0330
440
0.0062
0
0
0
6,338
0.09
1,308
0.02
412
0.006
0
Chío
216
0.0270
89
0.0029
2
0
0
1,698
0.05
931
0.03
1,285
0.040
Arafo
54,120
1.8500
47,031
0.4020
0
0
0
9,666
0.08
3,430
0.03
4,551
Boca Cangrejo
147
0.0070
107
0.0005
2
0
0
47,255
0.61
3,374
0.04
Garachico
96
0.0020
4
0.0000
0
0
0
54,597
0.42
5,293
Reventada
509
0.0170
134
0.0012
0
0
0
30,288
0.27
Fasnia
256
0.0130
40
0.0005
0
0
0
31,252
Chinyero
109
0.0040
2
0.0000
44
2
0
Güímar
915
0.0240
998
0.0068
0
0
0
1m
0.5 m
n
%
n
%
n
%
n
RMSE
%
n
±m
0
69
3.64
1+2 (out/inflow)
0.0014
68
3.74
0.040
0
0
151
3.77
6,642
0.090
3 (outflow)
0.0011
251
1.75
0.04
7,900
0.060
0
0
243
3.80
3,214
0.03
7,111
0.060
0
0
226
2.64
0.42
1,455
0.02
3,828
0.050
0
0
100
3.02
17,363
0.19
4,027
0.04
8,210
0.090
0
0
167
2.74
223,675
1.52
6,496
0.04
4,757
0.030
3 (outflow)
0.0002
257
0.56
17
Electronic Supplementary Material 2 Montaña Chahorra Montaña Chahorra is a multiple scoria cone located on the southern (upper) slopes of Pico Viejo stratovolcano generated by fissure eruptions in 1798 AD (Carracedo et al., 2007) lasting about three months (Romero, 1991). A large (4–4.5 km2) area was covered by mostly aa, pahoehoe lava flows mostly filled the W and SW part of the Las Cañadas caldera, with an average thickness of 7 m (Romero, 1991). The basement beneath the Chahorra vent is mostly evolved phonolitic lavas flows and pyroclastic rocks forming steep slopes (20–25° based on the DEM) of Pico Viejo stratovolcano (Carracedo et al., 2007). The Chahorra scoria cone lacks clearly recognizable cone geometry in spite of its young age. Chahorra scoria cone is located on steep slopes facing W (233°) with a slope of 24° (Table 1). The delimited flank area does not contain any pixels with upward directions. The other (S mean = 28°, Smedian = 29°, Smode = 29°) and downhill (Smean = 26°, Smedian = 26°, Smode = 29°) facing slope sectors are characterized by steep slope values. Interestingly, the S mode is the same in the cases of both flank sectors. A slight difference can be seen in the standard deviations (4° and 5°). The slope histogram of F other is unimodal, but distinct peaks can be found in the Fdownhill.
18
Montaña Chío The Montaña Chío is located on the southern slopes of Pico Viejo. The volcanic complex consists of two circle shaped craters and an additional, highly elongated (ca.780 m x 230 m in dimensions) and breached crater indicating that the loci of the explosion have most likely migrated along a narrow, W–S alignment path on the PicoViejo polygenetic volcanoes‘ slopes. The dominant eruption style of this cone was Strombolian-type on the basis of the preserved typical scoriaceous lapilli succession of the cone. The scoria cone eruption took place from 3933±212 yr BP (or between 2197 to 1772 BC) on the basis of radiocarbon dating (Carracedo et al., 2007). Montaña Chío scoria cones have formed by accumulation of normal to inverse graded welded and/or non welded pyroclastic deposits with symmetrical, fluidal and irregular shaped, unsorted pyroclastic fragments and intercalated lava units. Basement direction is 282.8° (or W) at the same time the inclination (14°) is the second highest among studied cones (Table 1). Uphill sector represented an insignificant proportion (only 0.02% from the total number) of pixels, therefore we discarded them from the interpretation. The F other (Smean = 23°, Smedian = 23°, Smode = 19°) and Fdownhill (Smean = 21°, Smedian = 19°, Smode = 15°) show relatively low slope values and large standard deviation around 8°.
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Montaña Garachico The Garachico (also known as Arenas Negras) is a horseshoe-shaped scoria cone with a lava flow field emplaced as a result of flank eruption in 1706 AD (Romero et al., 2006) in the north part of NW rift. The total volume of the emitted volcanic materials was calculated to be 0.045 km3, covering about 7.6 km2 around the volcanic edifice (Romero et al., 2006; Doniz et al., 2008). The related lava flow is about 6 km long, up to 2 km width and reaches the coastal region where it formed a small lava delta (app. 400x400 m). The small port and village of Garachico was partially destroyed by the fast flowing (460 m/hour) aa lava flow (Romero et al., 2006). The basement of Garachico is moderately inclined at ~6.6°. The direction of this basement is facing N (12.6°; Table 1). The largest numbers of pixels are located on the up- and downhill faced flank sectors. All of the slope angle histogram has nearly the same shape with distinct unimodal distribution. There are a few small peaks between 0 and 10°. The flank sectors have relatively large differences. The uphill sector is the highest in slope angle (S mean = 29°, Smedian = 29°, Smode = 30°), while the lowest is the downhill (S mean = 22°, Smedian = 23°, Smode = 23°) with the standard deviations 5°. The other flank sector is measured a slightly steeper 24° (Smean = 24°, Smedian = 24°, Smode = 25°).
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Montaña Reventada The Montaña Reventada is situated close to the base of Pico Viejo stratovolcano. The eruptions of Montaña Reventada are characterized by a special type of magma mixing erupting a single lava flow that contains both basaltic and phonolitic zones (Araña et al., 1994). The Montaña Reventada is the youngest non-historical eruption in Tenerife according to the latest radiocarbon dating published by Carracedo et al. (2007). Its age is about 895±115 yr BP (or between 900 and 1210 AD). Montaña Reventada has a multiple scoria cones composed dominantly of scoriaceous lapilli successions (Dóniz, 2009). Its small crater (~ 100 m in diameter) is symmetric in shape, but the larger one (~ 200 400 m dimensions) is deformed by emitted aa and block lava flows that covered about 1 km 2 on the northern part of NE rift zone. Basement inclination of the surface below the cone is around 5.8°. The general direction of dipping based on spot height data is 289.9° or W (Table 1). A scattered, skewed and multimodal histogram occurs in the case of Fuphill sector while the Fother and Fdownhill are more symmetric and unimodal in distribution. The Fother segment is the steepest around 26°. Significantly, gentler slope values can be found on the Fuphill (Smean = 22°, Smedian = 22°, Smode = 19°) and Fdownhill (Smean = 21°, Smedian = 21°, Smode = 19°). The standard deviations are between 4° and 6°.
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Montaña Chinyero Chinyero scoria cone is located in the central part of NW rift zone (Fig. 1) and represents the youngest (1909 AD) eruption event of Tenerife. The basement of the Chinyero scoria cone comprises mostly older lava flows and pyroclastic rocks from the older, Quaternary Montaña Chío and Montaña Reventada volcanoes (Carracedo et al., 2007). Chinyero resulted from a fissure eruption (length: 700 and width: 300 m) that formed different scoriaceous lapilli successions and a highly breached crater. The lava field of Chinyero covered a surface of 0.23 km2 with a maximum length of 4.5 km (Romero, 1991) and dominated by aa, pahoehoe and lava block surface characteristics. The present morphology of the volcano is highly asymmetric due to the lateral (S–SW dominated) lava emission during the course of the eruptions (Dóniz, 2009). Chinyero is located on a pre-eruptive surface that is gently sloping (3.3°) and facing toward NW (316.8°; Table 1). In spite of the asymmetric geometry of the edifice, both slope sectors can easily be determined in the DEM. The uphill slopes are the steepest in general (S mean = 29°, Smedian = 28°, Smode = 27°) with 7° standard deviation. The slope angle histogram is bimodal and skewed. More moderate slopes were measured on the other (Smean = 27°, Smedian = 27°, Smode = 24°) and downhill (Smean = 26°, Smedian = 26°, Smode = 27°) slope sectors with narrower standard deviations of 6° and 5°, respectively. These histograms are very similar, i.e. unimodal. However, total number of slope pixels is larger in the case of Fother.
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Montaña de Güímar Montaña Güímar is the only cone in this paper which has no age data. But the still intact morphology, moderate vegetation cover as well as limited gully-erosion indicate that it was built up during the Pleistocene to early Holocene era, several (tens of) thousands years ago. The scoria cone is also unique because it is situated on the southern coastal region of Tenerife. The present morphology of Güímar scoria cone is characterized by a symmetrical basal area and crater (Dóniz, 2009). The lava field (3.1 km2) is rich in superficial forms: pahoehoe, aa, block lava flows and associated lava tubes and jameos (collapsed lava tubes). The present morphology of the cone is very well preserved because the volcano is located in an area of semiarid climatic conditions. The Güímar scoria cone is located on a relatively flat coastal area making the calculation of pre-eruptive surface inclination problematic because of the lack of bathymetric elevation data and the extensive lava field around the cone. The inclination may not exceed 1° with direction of the dipping is 115° or SE (Table 1). The inner slope angle variance between slope parameters and flank segments is low and range between 26° and 31° with standard deviation up to 4°. The histograms are slightly skewed toward lower slope values and generally unimodal except the F uphill.
References for the Electronic Supplementary Material 2 Araña V, Martí J, Aparicio A, García-Cacho L, García-García R (1994) Magma mixing in alkaline magmas: An example from Tenerife, Canary Islands. Lithos 31(1-2):1-19 Carracedo JC, Rodríguez Badiola E, Guillou H, Paterne M, Scaillet S, Pérez Torrado FJ, Paris R, Fra-Paleo U, Hansen A (2007) Eruptive and structural history of Teide Volcano and rift zones of Tenerife, Canary Islands. Geol. Soc. Am. Bull. 119(9):1027–1051 Dóniz J (2009) Morphometric analysis of cinder cones on Tenerife (Canary Islands, Spain): results and applications. In: Romero Díaz A, Belmonte F, Alonso F, López-Bermídez F (eds) Advances in studies on desertification. Editum, University of Murcia, Murcia, pp 235-238 Doniz J, Romero C, Coello E, Guillen C, Sanchez N, Garcia-Cacho L, Garcia A (2008) Morphological and statistical characterisation of recent mafic volcanism on Tenerife (Canary Islands, Spain). J. Volcanol. Geotherm. Res. 173(34):185-195 Romero C (1991) Las manifestaciones volcánicas históricas del Archipiélago Canario. Consejería de Política Territorial. Gobierno Autónomo de Canarias, Santa Cruz de Tenerife, Spain Romero C, Beltrán E, Dóniz J, Coello E, Guillén C, Pérez-Lozao M (2006) The impact of 1706 Arenas Negras eruption at Garachico. A study from ancient engravings (Tenerife, Canary Islands, Spain). In: Garavolcán Meeting. Garachico, Tenerife, Spain
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