SSP3.1

Silica sinter systems occur in regions of magmatic intrusion, where silica-rich alkali chloride fluids rise to the Earth's surface. The Oligo-Miocene Etili silica deposits are one of the most well-known geothermal systems in Turkey, which occur mainly on E-W and NE-SW trending extensional faults with past associated magmatic activity. The mineralogical assemblage of the Etili epithermal system consists of kaolinite, halloysite, alunite +/- jarosite, and quartz. The most common silica polymorph detected in the sinters is -quartz. No other silica polymorphs were observed and proximal apron lithofacies were the only facies preserved in the region. Other lithofacies were not preserved due to erosion and tectonism. The lithofacies observed in the Etili epithermal systems include; silica infiltrates, spring conduits, nodular and finely laminated geyserite, sinter clast breccia, silicified volcanic rocks, and epithermal veins.
Hydrothermal alteration assemblages aged using the 40Ar/39Ar dating method indicate three distinct periods of hydrothermal activities that took place in different vacinities of the Etili Fossil Silica Sinter Region. These include: a) Early stage in the western part of the Etili ( 32.4 ± 1.2 to 22.6 ± 0.22 Ma), b) Intermediate stage in the eastern part of the Etili (12.3 ± 0.3 to 15.2 ± 0.3 Ma ) in the north of the Hamamtepe, and c) Late-stage to the south of the Etili (5± 0.18 to 7 ± 0.3 Ma). These chronological data indicate that the hydrothermal activity in the region started earliest in the west and shifted through to the east and/or south over time.
Keywords: epithermal system; hot spring; silica sinter; 40Ar/39Ar dating; hydrothermal alteration

How to cite: Ercan, H., Ece, Ö. I., Schroeder, P. A., and Gülmez, F.: Formation model of silica sinter deposits: an example from Western Turkey, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-638, https://doi.org/10.5194/egusphere-egu22-638, 2022.

Lacustrine sediments that fill volcanic craters like Lake Maninjau in West Sumatra (Indonesia) are pristine archives of past natural geological processes such as flooding, slope failure induced landslides, and volcanic eruptions. The aim of the study is to investigate the shape, and distribution of the morphological features found on the floor of Lake Maninjau as well as attempt the seismic stratigraphy of its basin fill. This is achieved by utilizing a 2-16 KHz Sub Bottom Profile seismic reflection survey that is complemented with a high-resolution sonar scanning (bathymetry) of Lake Maninjau.

The results show that the floor of Lake Maninjau is flat (~8 km wide) and reaches a maximum depth of ~168 m at the lake depocenter. Shallow sediment cores show that hemipelagic sediments predominantly cover its floor. The lake floor physiography is divided into five provinces (shelf, plateau, lake shoulder and slope, central sub-basin, and southern sub-basin), that are characterized by different morphological features with distinct responses on seismic data. These features include Mass Wasting Complexes (MWCs), blocks, gully-like features, and a lake-center dome. The MWCs are found in the northern, southern, and southeastern parts of the lake, and are occasionally characterized by embedded ~0.9-0.4 m high blocks that are interpreted to result from debris avalanches possibly accompanying earthquakes or extreme climate events. Debris flow sediments are identified on the sediments of the slope and basin shoulders, which are represented by locally constrained chaotic reflections that exhibit synchronicity. A central dome is well identified and interpreted to be of volcanic origin and may indicate a reactivation of the Maninjau volcano. The basin lacustrine infill consists of five seismic facies that serve to identify six seismic stratigraphic seismic units (SU I to SU VI), with each representing a distinctive phase in the lake evolution.

This study gives insights into the morphology and distribution of sub-lacustrine features identified within the basin fill of Lake Maninjau. It further confirms that Lake Maninjau archives past natural processes and lays the foundation for an improved understanding of the provenance of sediments and possible future utilization of the lake archive as a record of both environmental and climate change.

How to cite: Oladipo, O., Bouvet De La Maisonneuve, C., and Waldmann, N.: High resolution geophysical study of Lake Maninjau, West Sumatra, Indonesia, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-7938, https://doi.org/10.5194/egusphere-egu22-7938, 2022.

Lake sedimentary archives from volcanic regions frequently contain a rich and continuous record of tephra layers, providing a critical source of information to reconstruct a most complete eruptive history of neighbouring volcanic centres. Lake sediments from volcanic islands are particularly useful as the typical small size of these islands and their steep subaerial and submarine slopes lead to a lower preservation potential of primary pyroclastic deposits. Here we study the volcano-sedimentary record of Lagoa da Lomba (Lomba Lake), an old crater lake located in the central upland area of Flores Island (Azores), to gain insight into the recent volcanic history of this island. The strategic location of Lagoa da Lomba, half distance between the two clusters of recent volcanic activity of the island, together with its 23.52 cal kyr BP record, makes this lake a privileged site to investigate the Holocene volcanic history of Flores. We conducted a detailed characterization of the sedimentary facies from a transect of three cores to differentiate primary from reworked/redeposited tephra deposits, which was complemented by glass shard geochemical analysis and radiocarbon dating.

We recognized four eruptive events taking place between 6.28 and 2.36 cal kyr BP, demonstrating that the Holocene volcanic activity at Flores Island may have lasted longer than previously reported. Glass shard geochemistry from the different tephra layers suggests three populations, ranging from basaltic to trachybasaltic in composition, where the last eruption is the least evolved endmember. Two of the four eruptive events correlate geochemically and stratigraphically with subaerially-exposed pyroclastic sequences. The most recent event recorded at Lagoa da Lomba was constrained to 3.66 – 2.36 cal kyr BP and associated with an eruption sourced from Lagoa Comprida Volcanic System. The second most recent eruptive event was sourced from Lagoa Funda Volcanic System and dated at 3.66 cal kyr BP. Our observations show that Flores Island experienced vigorous volcanic activity during the Late Holocene. Therefore, contrary to what was previously assumed, the possibility of future eruptions should not be underestimated, and the volcanic hazard here should be properly assessed. Moreover, our results highlight the importance of tephrostratigraphy in recent lake sediments to reconstruct past volcanic activity in those contexts where outcrops exposure is limited.

This work was supported by SFRH/BD/138261/2018 doctoral grant and DISCOVERAZORES (PTDC/CTA-AMB/28511/2017) project funded by FCT (Portugal), and projects PaleoModes (CGL 2016-75281-C2) and RapidNAO (CGL 2013-40608-R), financed by MINECO (Spain). This work was also supported by project FCT-UIDB/50019/2020 - IDL funded by FCT.

How to cite: Andrade, M., S. Ramalho, R., Pimentel, A., Hernández, A., Kutterolf, S., Sáez, A., Benavente, M., M. Raposeiro, P., and Giralt, S.: The Lomba Lake sedimentary record over the last 23.5 ky: implications for the Holocene volcanic history of Flores Island (Azores), EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-8838, https://doi.org/10.5194/egusphere-egu22-8838, 2022.

Changbaishan Tianchi volcano is one of the most famous active volcanoes in Northeast Asia. Its Millennium eruption (ME, 946-947 CE) is considered to be one of the largest explosive eruptions over the past 2000 years, which had produced widely distributed tephra layer across Northeast Asia. However, little attention has been paid to the tephra buried in peatlands around this volcano. Here we present petrographic, geochemical and AMS¹⁴C data of the volcanic glasses within a new discovered macro-tephra layer buried in the Yueliangwan peatland, northeast China. The results suggest that buried tephra was the product of Changbaishan Millennium eruption. The eruptive sequence of the ME included comendite eruption and trachyte eruption from bottom to top. Tectonic background analyses reveal that Changbaishan Tianchi volcano fields belong to the anorogenic within plate back-arc extensional tectonic environments. Eruptive and sedimentary processes of the buried tephra were postulated as follows: a large amount of volcanic glasses formed through the eruption of trachyte magma that had high contents of rare earth elements (REE) and trace elements (TE). Then, fine grained volcanic glasses were sprayed into the atmosphere and transported to the Yueliangwan areas. The volcanic glasses deposited and formed airborne pumice layer. This buried tephra layer would act as a key isochronous marker horizon for the chronological framework in a range of sedimentary contexts across Northeast Asia. And it provides accurate eruptive sequence of Changbaishan Millennium eruption. This study would attract more attentions on the buried tephra in peatlands around active volcanoes, which would be of significance for the reconstructions of volcanic eruption history.

How to cite: Zhang, M.: The Changbaishan Millennium eruption tephra recorded in the Yueliangwan peatland, northeast China, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-613, https://doi.org/10.5194/egusphere-egu22-613, 2022.

A set of rhyolitic tuff-mudstone interbedded rock outcrop with good rhythm is developed in the Yangjiaodong area of Lingshan Island, eastern Shandong Province. In order to research the causes of the rhythm formation of the reflected volcanic eruption magmatic dynamics process, the collected sample were analyzed by time-scale series. The analysis model sets the thickness of tuffaceous rhyolite layer of the sample to represent the eruption scale and the thickness of mud layer represents the dormant time of volcanism. Combined with the geological background of the study area, the parameter deposition rate is the deposition rate of volcanic back-arc basin (6.5 m / Ma) with insufficient source supply, and the mudstone compaction factor is 0.3. Based on this, the thickness of different lithology was counted, and the time span of the analyzed sample was calculated to be 2.24Ma. Using Acycle software for quantitative data interpolation, detrending, spectrum analysis, filtering and other processing, got four scale and four kinds of eruption mode. Finally, the scale-time diagram was analyzed, and matched with the melt activation rheological lock-up window to obtain the volcanic activity pulse eruption model, so as to predict the near-surface magma chamber dynamics process.

How to cite: Liu, R.: Volcanic Sedimentary Rhythm Characteristics of Early Cretaceous Rhyolite Tuff in Lingshan Island, Eastern Shandong Province and its Indication to Magmatic Dynamic Process, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-827, https://doi.org/10.5194/egusphere-egu22-827, 2022.

Volcanic eruptions and submarine landslides and may have occurred frequently among the central Azores (Faial, Pico, São Jorge, and Terceira islands) because landslide valleys are abundant on their submarine slopes and dark volcaniclastic beds are common in sediment cores. The threats of future such processes need evaluating for citizens living on the islands. A multidisciplinary approach was applied to provide a hazard assessment based on high-resolution multibeam bathymetric data and four gravity cores collected in basins amongst the islands.

More than 1200 submarine slope valleys were documented from the bathymetric data. Based on their morphological features, >300 of them were interpreted to be likely of landslide origin and produced by single slope failures. Thirteen of them would probably have generated tsunamis with heights at source 1-7 m. This may explain some tsunamis recorded in the area that cannot be assigned to earthquakes. Different landslide abundances and mean volumes were also found between two groups of islands. There are more and smaller landslides in one group (Faial and Pico) compared with fewer but larger landslides around another group (São Jorge and Terceira). This may be explained by a more frequent triggering of slope failure around Faial and Pico, which prevent the accumulation of thick superficial deposits, or sediment densification by ground shaking. This may suggest a greater threat from large earthquakes among these two islands that is not currently found in earthquake records.

The sediment cores were analyzed to interpret whether emplacements of volcaniclastic beds were from tephra fallout, pyroclastic flows or submarine landsliding. This required assessing various information, including sedimentary structures, glass shard geochemistry and morphometrics, bulk composition and organic geochemistry. From the results, 2/3 of the volcaniclastic beds originated directly from erupting volcanoes, whereas only 1/3 involved slope remobilization such as landsliding. The modal thickness of the volcaniclastic beds is small (2-20 cm). The low incidence of beds of landslide origin could be explained either by landslide-generated sediment flows infrequently reaching the basin floors and/or eruptions creating beds more frequently. Based on ¹⁴C datings, all types of turbidity currents have reached the core sites at a modest frequency since the Last Glacial Maximum (0.45 events/kyr on average).

How to cite: Chang, Y.-C., Mitchell, N., Quartau, R., Hansteen, T., Schindlbeck-Belo, J., and Freundt, A.: Geological hazard assessment of volcanic islands: Insights from seafloor geomorphology and turbidites in sediment cores, central Azores Islands, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-1025, https://doi.org/10.5194/egusphere-egu22-1025, 2022.

The evolution of the largest composite volcano in the Zărand basin of the Apuseni Mts., named recently Bontău has been associated with close-by dome complexes. It was built by calc-alkaline lavas and pyroclastic deposits (basaltic andesites to andesites). According to the available K/Ar data the Bontău Volcano is known to be active roughly between ~14-10 Ma and presently is covering an area of ~ 807.22 square km.

The initial edifice of the volcano is presently not anymore conserved and now the Bontău volcano it is composed of central edifice remnants named NDD, CVE and CVW surrounded by debris avalanche (DADs) and associated debris flow deposits. The stratovolcano had two stages; first effusive-explosive generated in the same time with the Gurahonţ, Aciuţa and Vârfuri close-by Domes up to ~12 Ma. The second stage, after ~12 Ma started with effusive dome at the top of the Bontău volcano. Further Plinian eruption and then gravitational collapses have emplaced massive volume DADs, widely distributed all around the volcano. Four DADs units are defined, corresponding to collapsed structures directed initially to the west and east and then to the south and north. This is the first calculations volumes of the Bontău volcanic complex, including edifice remnants, associated Domes and the DADs with the intention to reconstruct the initial edifice of Bontău volcano. DADs cover an extensive area around the former volcano edifice; around 346.14 square km and the central edifice remnants cover around 40.65 square km. Two DADs units surrounding the remnants of the former volcanic edifice are E-W directed (EDA, WDA) and the other two are N-S directed (NDA, SDA). The largest unit it is the EDA and characterized by highest run out of debris avalanches (~19 km) filling the Zărand basin interior. The calculations took into account the Pliocene-Quaternary erosion processes including the Crişul Alb River and its tributaries. According to volume calculations we reconstructed the volcano edifice that most probably had a base diameter of ~ 12 km and a height of ~2096 m. The edifice is looks similar in size with other composite volcanoes (i.e., present day Ruapehu volcano, North Island, New Zealand).

How to cite: Mirea, V. M. and Seghedi, I.: Miocene Bontău volcanic complex (Apuseni Mts., Romania); volume calculations and edifice reconstruction, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-12303, https://doi.org/10.5194/egusphere-egu22-12303, 2022.