See discussions, stats, and author profiles for this publication at: https://www.researchgate.net/publication/279298974 DEM-based analysis of the morphometry of lava domes; a case study from the Taupo Volcanic Zone, New Zealand Conference Paper · June 2015 CITATIONS READS 0 211 5 authors, including: Szabolcs Kósik Karoly Nemeth Massey University Massey University 48 PUBLICATIONS 159 CITATIONS 494 PUBLICATIONS 5,381 CITATIONS SEE PROFILE SEE PROFILE Shane J Cronin University of Auckland 364 PUBLICATIONS 7,529 CITATIONS SEE PROFILE Some of the authors of this publication are also working on these related projects: Evolution of magmatic systems in development of a long-lived caldera-producing volcanic field View project Whats happen next? Modeling the eruption pattern of monogenetic volcanoes [MURF 2016] View project All content following this page was uploaded by Szabolcs Kósik on 17 August 2015. The user has requested enhancement of the downloaded file. DEM-based analysis of the morphometry of lava domes; a case study from the Taupo Volcanic Zone, New Zealand Szabolcs Kósik¹*, Károly Németh¹, Jonathan Procter¹, Gábor Kereszturi¹, Shane J. Cronin¹ ² *email: [email protected] 1. Ins tute of Agriculture and Environment, Massey University, Palmerston North, New Zealand, 2. School of Environment, University of Auckland INTRODUCTION Lava dome with volume Lava dome with volume Lava dome with volume Lava dome with volume The Taupo Volcanic Zone (TVZ) has about 300 silicic lava domes and coulees, emplaced over the last 500 000 years. In comparison with scoria cones (F ., 2012), the syn-erup ve morphometry of lava domes is much more diverse due to the greater variability in the physical and chemical proper es of the erup ng magmas. The shape of a growing lava dome is influenced mostly by the viscosity of the erup ng melt, the inclina on of the pre-erup on surface and erosive processes, such as collapses, but other factors have an influence, such as magma yield strength, cooling rates, degassing processes, effusion rates and the dura on of the erup on (H ., 2014; Y , 2005). The TVZ provides an ideal loca on for the geomorphological characterisa on and classifica on of lava domes. Domes related to the TVZ caldera system are generally aligned and clustered around the NE-trending fault system, and are distributed across a number of volcanic centres of varying ages. The extractable morphometric parameters (slope angles, edifice volume, elonga on of the volcanic edifice and its orienta on) together define the morphometry of the lava domes, which clearly reflects both the syn-erup ve (e.g. the viscosity of the magma, explosive behaviour during of dome growth, dome collapsing) and the post-erup ve processes such as faul ng, erosion, valley incision and degree of mantling. Pohaturoa Okataina 25 km Oh. Reporoa Fig. 1a. Edifice elonga on orienta on of the lava domes of the TVZ. 170° 35° TV Whakamaru 40° Age: 133-168 ky A: 0.43+ km² H: 262.1 m V: 0.03+ km³ Age: 14 ky A: 1.99+ km² H: 165.3 m V: 0.21+ km³ Age: 0.7 ky A: 3.0 km² H: 489.5 m V: 0.86 km³ 45° Taupo 2 km 2 km Te Horoa Mokauteure Age: 68-125 ky A: 5.82+ km² H: 302.5 m V: 0.83+ km³ Age: 128-524 ky A: 3.61+ km² H: 383 m V: 0.49+ km³ 1 km Age: 8 ky A: 7.45+ km² H: 188.3 m V: 0.93+ km³ 1 km Tongariro Ngauruhoe 1 km 5 km Fig. 2. Examples for different lava dome morphologies and three morphometric parameter from the TVZ. (A = Area, H = Height, V = Volume) At coulees the arrows show the main flow direc ons. Fig. 1. Spa al distribu on and edifice volumes of the lava domes and coulees within TVZ. The inset (b) shows the outlines of 324 domes (the dome posi ons at the inset do not reflect their real loca ons). Ruapehu MATERIALS AND METHODS We mapped the volcanic structures of the TVZ (Fig 1.) using DEM derivates (eg. slope, aspect) of a Digital Eleva on Model with 8 m resolu on, 1:250K geological maps of New Zealand and the 1:50K geological map of Okatania Volcanic Centre. The 8 m DEM was primarily derived from contour lines with 20 m intervals (LINZ Topo50). The spa al accuracy is within ±22 metres horizontally and within ±10 metres ver cally. For GIS analyses we used ESRI ArcGIS 10 and Golden So ware Surfer 10 so wares. We precisely delimited the lava domes based on the morphological parameters of the surface. As a result we could calculate the dome parameters, such as area, height, average slope, volume, circularity and orienta on. In this study we used the averaged ages of the ages are given on the 1:250K geological maps (Fig. 7d). In the first stage, we have applied the Height/Diamater ra o to evaluate the lava domes within the TVZ (B , 1990) (Fig. 4). Finally, we inves gated the slope and eleva on distribu ons of the domes (Fig. 3), and we determined the height posi on of the steepest slopes for individual lava dome edifices (Fig. 6). 750 dacite rhyolite es om s nD e om D ava L w -P elé ea 550 e= p Slo - Lo b pe =1 .06 Wahanga 5 0.5 Slo 400 Mokauteure Name of Volcano Loca on Year of emplacement Rock type Nevados de Chillan Chile 1981 andesite Shiveluch Russia 1980 andesite Puluweh Indonesia 1981 andesite Novy (Bezymianny) Russia 1956 andesite Great Sitkin USA 1974 andesite Mt. St. Helens USA 1984 dacite Mt. Pelée Mar nique 1903 andesite Lamington Papua New Guinea 1955 andesite San aguito Guatemala 1922 dacite Lassen Peak USA ~1000 BC? dacite Rangitukua 350 Pohaturoa 200 TED Te Horoa 150 100 c Fig. 4b. Lava domes used for parametriza on of Peléan Domes by Blake (1990). 50 0 0 100 200 300 400 500 600 700 800 900 1000 1100 1200 1300 1400 1500 1600 1700 1800 1900 2000 2100 2200 2300 2400 2500 2600 2700 2800 2900 3000 3 80% 2 60% 1 40% 1 20% 2 0 10 20 30 40 50 60 0% 70 80 90 rela ve frequency of steepest slopes (degree) 5 RANGITUKUA 80% 60% 2 40% 1 20% 2 0 0% 20 30 40 50 60 rela ve eleva on (degree) 70 80 90 10 0 60% 2 40% 1 1 20% 0% 20 30 40 50 60 70 80 90 rela ve eleva on (degree) 100% 3 80% 10 120% 4 10 3 0 140% 1 100% 10 0 cumula ve frequency (%) rela ve eleva on (degree) 120% rela ve frequency of steepest slopes (degree) 100% WAHANGA 4 5 5 MOKAUTEURE 80% 60% 2 40% 4 1 0 10 1 20 2 30 40 20% 3 50 0% 60 rela ve eleva on (degree) 70 80 90 3 10 0 80% 2 60% 1 40% 1 1 20 20% 1 30 40 0% 50 60 70 80 90 rela ve eleva on (degree) 100% 3 120% 100% 10 120% 1 TARAWERA EASTERN DOME 0 140% 4 140% 4 10 0 cumula ve frequency (%) rela ve frequency (%) 120% 100% 1.5 80% 1 60% 40% 0.5 2 120% 100% 1.5 80% 1 60% 40% 0.5 20% 0 20% 0% 10 20 30 40 50 slope angle (degree) 0 10 60 20 30 40 50 60 70 80 90 0% 100 rela ve eleva on (%) Two morphometric classifica ons exist for lava domes. The first one was carried out by B (1990) based on field observa ons and laboratory experiments, and has been dis nguished four types of lava domes (Upheaved plugs, Peléan domes, Low lava domes and Coulees) by the height versus diameter ra o of the edifice. We have reviewed those results and we found three important circumstances about the inves gated Peléan domes; the volcanoes produced lava domes are located in volcanic arcs, all the domes were piled up above a central vent of a composite volcano; and there was no lava dome with rhyoli c chemical composi on. The other classifica on was based on improved laboratory experiments, field observa ons and photographic analyses (F G , 1998). The classifica on schemes grouping the lava domes into four types (spiny, lobate, platy, and axisymmetric) that eventually relates to erup on condi ons, the morphology and the surface texture of the dome, and the thickness of the forming carapace. Their study did not provide any quan fiable data about morphometrical parameters of the dis nc ve classes. GIS-based morphometric characteriza on of 29 worldwide lava domes was carried out by K ., (2013) with the aim of rela ve da ng of lava domes using slope angles. Since K . (2013) did not classify the examined domes, thus rela ve ages are tenta ve as long as it is presumable, that condi ons during dome growth are reflected on the slope angles and posi on of the steepest slopes too. The lava domes within the TVZ have o en complex morphology, therefore do not fit into Blake`s classifica on (Fig. 4). Thus we tried to find a new method for classifica on, namely we examined the loca ons of the steepest slopes as a func on of rela ve eleva on (Fig. 6). We believe, steepest slopes posi on reflects the differences of viscosity and magma yield strength during emplacement, however it can be modified by erosion. 140% TE HOROA 120% 4 3 25 120 # 100% 80% # a: volume 100 b: circularity 20 60% 2 80 40% 15 1 1 0 10 20 30 40 20% 1 50 60 rela ve eleva on (degree) 60 0% 70 80 90 10 0 10 40 Fig. 6. The steepest slopes (highest 200 values and addi onal 2 degree of slope percent from slope raster) as a func on of its rela ve height for the example domes (Fig. 1, 2, 3, 4 and 5). These histograms show mul ple modes, here we interpreted these modes due to erup ve processes, such as number of extrusion phases (numbers in yellow). In contrast, the coulees (Tarawera Eastern Dome and Te Horoa) are characterized by only one lava erup on should show a con nuous values with low rela ve frequency of the steepest heights. each peak belongs to one erup on, Steep slopes are also generated by faults and river incision a er the dome emplacement, thus the effected areas with external factors should be eliminated. 20 5 0 0.25 0.5 0.75 1.0 1.25 1.5 1.75 35 # 20° c: average slope 30 d: age of the domes 3 18° 35 16° 74 54 12° 25 7 69 14° 58 R² = 0 .1275 3 8° 0 50 100 150 200 250 300 350 400 (ky) 450 age500 20 15 10 5 0 55 10 10 15 20 15 20 slope (degrees) 0 0.2 10° We examined the morphology of lava domes in the Taupo Volcanic Zone using DEMs and DEM derivates. We obtained various morphometric parameters such as edifice volume, edifice height, average and maximum slope (Fig. 7). In comparison with other studies (K , 2013), our slope data show significantly higher values for maximum slopes (average max slope for 323 TVZ edifice is 43.1 degree). The height and diameter ra os do not fit to the regression lines specified by B (1990), which can be par ally explained by the complex emplacement history and post-emplacement burial and erosion of domes in the TVZ. The exis ng lava dome classifica ons can be taken into account with doubt or cannot be used for comparison with real data. TVZ’s dome morphologies show complex, some mes polygene c evolu on, which could be demonstrated by the defini on of the height posi ons of steepest slopes (Fig. 6). The height distribu on clearly shows the number of dis nct lava erup ons or the changes in magma yield strength during the emplacement. We presume, that the lava domes can be characterized by higher viscosity and lower yield strength, the steepest slopeswill be located at the upper third of rela ve height due to the debris flows of the talus apron do not allow steeper slope than 30-40 degrees (F M , 1990). Contrary, steepest slopes at the lower third of the rela ve height of the dome indicate lower magma viscosity, and probably the rela vely fast-cooling, bri le part (talus) will provide the steepest slopes with similar values like apron at viscous domes. Based on morphology, we can dis nguish the two extremes: ver cally growing and laterally growing domes (coulees). 2.0 volume (km³) CONCLUSIONS 25 25 30 30 35 0.3 0.4 0.5 0.6 0.7 0.8 0.9 Fig. 7. Histograms of three morphometrical parameters of the domes of the TVZ. Volumes: For precise calcula ons it is essen al to obtain the borders and the total height of the edifices. Using our raw data we could only provide minimum volumes or surficial volume in many cases. 40% of the edifice volumes are less than 0.1 km³. Dome circularity and orienta on: There are two significant peaks of the circularity distribu on. The lower peak at 0.55 which is the manifesta on of the tectonically influenced fissure orienta ons. The orienta ons of the dome elonga on are parallel with the extensional axis of the TVZ (Fig 1a). Average slopes: At this stage of the research we could only provide average slopes for all the edifices, but the results clearly show the effects of faults in the distribu on. At the inves ga on of individual edifices we eliminate these effects and others like river incision. Age of the domes: First approxima on of the average ages from geological maps, allows us to make a rough es ma on on the temporal distribu on of the domes. We found 5 periods, when the majority of the domes were formed: 0-25ka, 55-80ka, 150-170ka, 195-230ka and 320-340ka. Compared the average ages with average slopes we found a slightly decreasing trend of slope angles with me. REFERENCES B F F F H K Y View publication stats 140% 10 0 5 rela ve frequency of steepest slopes (degree) 120% 140% cumula ve frequency (%) POHATUROA 4 5 rela ve frequency of steepest slopes (degree) 140% rela ve frequency of steepest slopes (degree) rela ve frequency of steepest slopes (degree) 5 cumula ve frequency (%) cumula ve frequency (%) edifice radius (m) Fig. 5. Panoramic photos of three example lava domes. a: Pohaturoa, b: Rangitukua, c: Wahanga cumula ve frequency (%) 300 250 ELEVATION 140% 2 cumula ve frequency (%) edifice height (m) 450 160% MORPHOMETRIC CLASSIFICATION OF LAVA DOMES TED = Tarawera Eastern Dome 500 2.5 Fig. 3. Slope (orange) and eleva on (green) histograms of Pohaturoa lava dome (Fig. 5) with cumula ve frequency (black and red lines). Both histograms show that distribu ons have two peaks due to two an ini al, low profile dome overlaid by a more viscous dome (Fig. 6). 650 600 160% SLOPE a Fig. 4. Radius versus height of lava domes (with chemical composi on) of the TVZ. The Peléean Domes values are lower than the world average previously given by Blake (1990). The domes encompassed by the pink dashed line area are probably buried, therefore their total heights are underes mated. andesite 2.5 cumula ve frequency (%) Rangitukua b 2 km rela ve frequency (%) vent 700 175° Z Slope angle 3° > 3° - 7° 7° - 13° 13° - 18° 18° - 23° 23° - 28° 28° - 34° 34° - 40° 40° < Rotorua Topographical margins of silicic calderas (Oh. = Ohakuri) Tarawera Eastern Dome Wahanga < 0.1 km³ 0.1 km³ - 1.0 km³ 1.0 km³ - 2.0 km³ > 2.0 km³ , S. 1990: Viscoplas c models of lava domes. In: Fink, J.H. (Ed.), Lava Flows and Domes: Emplacement Mechanisms and Hazard Implica ons. Springer, New York, 88–126. , J.H. 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