# Scenario-based hazard assessment of Mt Hasan Stratovolcano, Central Anatolia, Türkiye

Erkan Aydar, Philippe Labazuy, Caner Diker

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Erkan Aydar, Philippe Labazuy, Caner Diker. Scenario-based hazard assessment of Mt Hasan Stratovolcano, Central Anatolia, Türkiye. Bulletin of Volcanology, 2025, 87, pp.37. 10.1007/s00445-025-01818-z. hal-05046312

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# Scenario-based hazard assessment of Mt Hasan Stratovolcano, Central Anatolia, Türkiye

Erkan Aydar<fnref n="1" />,<fnref n="2" /> ID · Philippe Labazuy<fnref n="2" /> · Caner Diker<fnref n="1" />

Received: 21 October 2024 / Accepted: 21 March 2025

© The Author(s) 2025

## Abstract

Mount Hasan (Türkiye), an active stratovolcano, has had two eruptions during the Holocene and currently exhibits fumarole activities at its summit. Despite its potential hazards, it is not under any monitoring. In a first-of-its-kind study in Türkiye, we utilized VolcFlow and TephraProb (Tephra2) codes to conduct a scenario-based probabilistic hazard assessment and forecast the explosive behavior of Mt Hasan during a volcanic eruption. In our scenario-based hazard assessment study, tephra fall deposits primarily accumulate from plumes dispersing in the NE, E, and SE directions, with occasional accumulation in the SW direction. Eruption source parameters, such as eruption duration, discharged mass, and plume heights, naturally affect the impact rate. The plume heights selected for modeling are (min-max) 5–10 km, 10–15 km, 15–20 km, 20–25 km, and 25–30 km to illustrate related tephra dispersal. All probability and probabilistic isomass maps have been drawn. Volcanic flows were modeled considering the topographic effects using the digital elevation model of the volcano. As a result, an approach was made especially to probable depositional areas and thicknesses. In conclusion, this study identified the areas most likely to be impacted by tephra deposits (fall, flow) given the scenarios applied and developed a comprehensive impact maps. Our findings underscore the urgent need for close monitoring of Mt Hasan.

**Keywords** Hazard · Impact · Scenario · Eruption · VolcFlow · TephraProb

## Introduction

Given the significant impacts of volcanic eruptions on societies, the environment, and the economy, it is crucial for decision-makers to have access to probabilistic eruption forecasts. These forecasts are essential for taking precautions and rational risk-reducing actions in crises, future land use, and emergency planning requirements (Marzocchi and Bebbington 2012). Numerous numerical simulations, codes and statistical methods have been developed to define areas expected to be affected by eruptions (Aravena et al. 2023). Although modeling codes are not limited to these, Ash3D (v.2.0-Mastin

et al. 2021), Fall3D (Costa et al. 2006), Tephra2 (Bonadonna et al. 2005), and TephraProb Toolbox (Biass et al. 2016) are widely used for Tephra fall modeling, while Titan2D (Pitman et al. 2003; Patra et al. 2005), Flow3D (Kover 1995), LaharZ (Iverson et al. 1998; Schilling 2014), and VolcFlow (Kelfoun and Druitt 2005) are also used for PDC and Lahar flows. Volcanic eruptions can cause various hazardous phenomena that disrupt daily life and cause significant economic losses (e.g., Durant et al. 2010; Biass et al. 2024). They threaten public health, critical infrastructure services, aviation, and agricultural production (e.g., Barsotti et al. 2018; Biass et al. 2024; Durant et al. 2010; Spence et al. 2005), and airborne particles also create serious health problems by deteriorating air quality (World Health Organization 2021). Airborne ash can be regenerated through the remobilization of previously deposited ash by the wind. (Jarvis et al. 2020; Aydar and Akkaş 2022). To study its trajectory and dispersal patterns, NOAA's HYSPLIT Atmospheric Transport and Dispersion Modeling System (Hybrid Single-Particle Lagrangian Integrated Trajectory model by Draxler and Hess 1998, and Stein et al. 2015) may be used (Aydar and Akkaş 2022). Different eruption dynamics can lead to varying effects in

Editorial responsibility: A. Tadini

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Erkan Aydar
eydar@hacettepe.edu.tr

<footnote n="1">¹ Dpt of Geological Engineering, Hacettepe University, Beytepe, 06800 Ankara, Türkiye</footnote>

<footnote n="2">² CNRS, IRD, OPGC, Laboratoire Magmas Et Volcans, Université Clermont Auvergne, 63000 Clermont-Ferrand, France</footnote>
volcanic eruptions. While ballistic blocks are destructive in proximal areas (Brown et al. 2017), lava flows and PDCs can also affect the medial and distal parts of the volcano. Besides, the tephra may be carried thousands of kilometers through the air and cause distal impact (Biass et al. 2024). The potential impacts of volcanoes on the surrounding areas are significant, making volcanic monitoring critical to mitigate the damage. Believing in “The most dangerous volcano is the unknown one,” we would like to mention that the Turkish volcanoes are poorly known in volcanological literature. The Global Volcanism Programme (Global Volcanism Program 2024) indicates that 7 Turkish volcanoes were active during the Holocene period. We believe this is a minimum number of potentially active volcanoes in Türkiye. Some of these volcanoes’ eruptions have been documented in the historical records (Karakhanian et al. 2002). In addition to stratovolcanoes and monogenetic vents (cinder cones, maars, domes), very conspicuously, shield volcanoes are also present in Türkiye (e.g., Tendürek, Karacadağ) on thickened continental crust. The main volcanoes are Mt Ararat (5137 m, 02 July 1840 AD phreatic eruption, Karakhanian et al. 2002), Mt Süphan (4058 m), Nemrut Caldera volcano (2935 m, last known eruption 1692; Aydar et al. 2003), Tendürek Shield volcano (3514 m, last eruption around 1877 AD; Karakhanian et al. 2002), Mt Erciyes (3917 m, at least four separate eruptions during the Holocene; Sarıkaya et al. 2019), Mt Hasan (8964 BP; Schmitt et al. 2014). Besides, monogenetic vent fields in Karapınar, Eğrigöz, Acıgöl, Derinkuyu, and Nevşehir regions also reach the upper Pleistocene and Holocene ages (e.g., Aydar 1992; Aydar et al. 1995). On the other hand, in western Anatolia, the Gölcük volcano produced ash flows that extended to N-NE toward Isparta city during the Holocene (Atıcı et al. 2023). Moreover, a Bronze Age activity is reported for Kula volcanism (Ulusoy et al. 2019), which consists of at least 80 monogenetic vents. Turkish active volcanoes are near urban areas and settlements, but none of those volcanoes are monitored. Many cities, towns, and other settlements are in unknown volcanic danger. Since there is no volcanic activity in the social memory, the belief that there are no active volcanoes in Türkiye is also ingrained in people's consciousness. Volcanic hazards and risk studies are infrequent in Türkiye, and so far, only the hazard map of Nemrut volcano has been published by Aydar et al. (2003). We are assessing hazards from tephra fall and pyroclastic flows at Mt Hasan using the VolcFlow code (Kelfoun and Druitt 2005) and the TephraProb toolbox for MATLAB (Biass et al. 2016). These codes were selected specifically because of the authors' preferences, rather than any advantages they may have over other similar codes. Scenario-based analysis of Mt Hasan volcanism allowed us to propose, for the first time, possible impact zones and hazard maps on local and regional scales.

## Geology of Mt Hasan

Mount Hasan is a composite stratovolcano with two peaks, namely big (BHD) and small Mount Hasan (SHD) (3253 and 3069 m, respectively) (Fig. 1). The base of the volcano is around 1000 m above sea level (asl). Its edifice was constructed over multiple stages identified as Paleo-, Meso-, and Neo-Hasan Dagi by extrusive dome emplacement and intermittent collapse events associated with ignimbrites (Aydar 1992; Aydar and Gourgaud 1998). Limited geochronological data indicate the emplacement of the oldest lavas (Paleovolcano) at 7.21 ± 0.01 Ma (K-Ar) (Aydar and Gourgaud 1998), and ignimbrites emplacement during an early caldera collapse at 6.31 ± 0.20 Ma (⁴⁰Ar/³⁹Ar), contemporaneous with wide-spread Neogene ignimbrite volcanism in Cappadocia (Deniel et al. 1998). The radiometric ages for Meso-volcano are rare but give 0.58 Ma (K-Ar age, Ercan et al. 1990) and 0.53 ± 0.05 Ma (Ar-Ar dating on Hornblende, Aydin et al. 2014). The Neovolcano stage started with dome extrusions with associated block-and-ash deposits (BAF), peripheral scoria cones and maars and subsequent ignimbrites (0.390 ± 0.05 Ka, Fission Track on obsidian lithics in ignimbrite by Bigazzi et al 1997). The Neovolcano, comprising two summits, bears numerous collapsed andesitic to rhyodacitic lava domes on its flanks, creating a wide-spread pyroclastic deposit. Debris avalanche deposits outcrop north of the volcano, on the plain, forming a typical hummocky surface. The main pyroclastics associated with those deposits are blocky-chaotic mass flows and biotite-rich pumiceous fall and flow units (U-Pb zircon ages: dated to 339 ± 50 Ka by Aydın et al. (2014) or to 0.44 ± 0.01 Ma, 0.35 ± 0.05 Ma and 0.34 ± 0.05 Ma by Sönmez et al. (2018) that outcrops on eastern flank of SHD, on the pass between neighboring Keçiboyduran volcano (a Pleistocene volcano: 2.21 ± 0.06 Ma; 1.26 ± 0.18 Ma; Sönmez et al. 2018). Friedrich et al. (2020) supply ZDD (Zircon Double Dating) U-Th/He ages of 7 lava flows ranging between 91.9 ± 3.9 and 18.1 ± 2.4 Ka and an age from block-and-ash-flows as 13.5 ± 1.5 Ka. Tuzgölü fault cut the N-NE foothill of Mt Hasan. Many lava flows are on the fault line, outward and inland on the volcano slope. These lava flows date back to 84 ± 4 Ka (K-Ar age, Kılıçtepe, Kuzucuoğlu et al. 2020), 99 ± 4 Ka (K-Ar age, Kuzucuoğlu et al. 2020), <100 Ka (K-Ar, Big lava flow around Belbashanı, Aydar 1992), 39.0 ± 1.0 and 151 ± 3 Ka (ZDD-U-Th/He, Gençoğlu-Korkmaz et al. 2024). The block-and-ash flows with 2–10 m thick sequences cover almost all flanks of BHD (SI-Fig. 1). They are deeply affected by channel erosion and intensely carved leading to the development of a dense drainage network on the volcano and the formation of deep valleys (Fig. 2). During the rainy season, country roads on the BHD slopes
<figure><img src="image_3.png" /><figcaption>**Fig. 1** Geological map of Mt Hasan Stratovolcano, modified from Aydar (1992). The legend is given chronostratigraphically, and the term “generation” is used for the same type of volcanic rocks</figcaption></figure>

placed at different times. For more information, see Aydar (1992) or Aydar and Gourgaud (1998)
<figure><img src="image_4.png" /><figcaption>**Fig. 2** a Sentinel 1 C image of Mt Hasan, b A facies map with lava and pyroclastics</figcaption></figure>

<figure><img src="image_5.png" /></figure>
deteriorate and slide due to the remobilization of uncon-
solidated, loose BAF deposits (cold lahar). Rhyodacitic-
Rhyolitic (Mesovolcano) and Rhyolitic (Neovolcano)
unwelded ignimbrites are restricted to the lower reaches
of the Neo-volcanic edifice in the N, S, and W. BHD sum-
mit has two nested craters dated to 29 and 33 Ka (K-Ar
age, Kuzucuoglu et al. 1998). Moreover, a large pumice
block about 50 cm in diameter, collected from the southern
foothill within the slope debris, gave an age of about 28.9
± 1.5 Ka (ZDD; Schmitt et al. 2014). Besides, an andesitic
lava dome extrusion on the north flank is around 6 Ka old
(Aydar 1992). Recently, airfall pumices collected from the
summit of BHD were dated to 8.97 ± 0.64 Ka (ZDD, U-Th/
He; Schmitt et al. 2014). This eruption was eyewitnessed
and depicted on a wall sketch at the Neolithic settlement
of Catalhoyuk. The wall painting is considered the oldest
depiction of a volcanic eruption and a contender for being
the first graphical representation of a landscape or a map in
the world (Clarke 2013; Sigurdsson et al. 2000).

Ulusoy et al. (2018) demonstrate that Mt Hasan is a very
deformed volcano and represents hot spots with fumarolic
activities at the summit (gas temperature reaching 50 °C)
giving self-potential (SP) anomalies. The hydrothermal zone
starts above 2250 m (Diker et al. 2018). Around 3000 m,
68.7 °C gas temperature was measured in fumaroles where
CO2 content reached 10,000 ppm (Diker et al. 2018; Diker
et al. 2023). Recently, Biggs et al. (2021) examined Turk-
ish volcanoes, especially Mount Hasan, using the InSar
technique for 2015–2020 and did not find any centimetric
scaled deformation. On 20 September 2020, a seismic crisis
occurred with a 5.1 Mw earthquake and over 100 aftershocks
in the southern region of Mt Hasan (SI-Fig. 2). Aydar et al.
(2021) conducted a study on the potential impact of the
seismic crisis on the volcano. At the summit fumarole that
reached 72 °C, they found a CO2 concentration of over 10%
(100,000 ppm), a Radon gas level of 3000 Bq/m³, and a low
SO2 concentration (1.2 ppm) (Aydar et al. 2021). Based on
these findings, they defined the activity as non-magmatic
unrest and suggested the possibility of a phreatic explosion.

Volcano monitoring primarily utilizes three methods: geophysical (including seismic, magnetic, electrical, and acoustic measurements), geochemical (focused on gas and water chemistry), and geodetic (such as tiltmeters and interferometric synthetic aperture radar (InSAR)). Unfortunately, there are no water springs on or around Mt Hasan, which limits our ability to monitor changes in water chemistry. Moreover, the effectiveness of magnetic and electrical measurements is contingent upon having established background values, which we currently lack. Geodetic methods can only be implemented during crisis situations to assess ground deformation associated with magmatic uplift. Consequently, in emergencies, seismic and gas measurements should take precedence as the primary monitoring techniques.

**Materials and methods**

Satellite image, digital elevation model

A digital elevation model (DEM), a raster representation
of the Earth's surface, is a precise mathematical model
of the Earth's terrain, represented as a grid of eleva-
tions (Li et al. 2005). ASTER Global Digital Elevation
Model (ASTGTM GDEM v3, 30 m spatial resolution;
LPDAAC, https://lpdaac.usgs.gov/products/astgtmv003)
and ALOS PALSAR Digital Elevation Model (12.5 m
spatial resolution; https://asf.alaska.edu/data-sets/deriv
ed-data-sets/alm-palsar-tmc/alm-palsar-radiometric-terra
in-correction) were used to create topographic elements
(slope and aspect maps) and drainage network maps for
hazard map production in ArcGIS v10.8. Both eleva-
tion models were used in VolcFlow modelling. Sentinel-
2 Level 1 C satellite image (date: 01.August.2021) was
downloaded via Copernicus Open Access Hub (https://
browser.dataspace.copernicus.eu/). The probability of
tephra accumulation models (outputs of TephraProbe)
was embedded in the Google Earth Pro program (Google
Earth V 7.3.6.9796. (10 April 2013/14 December 2015),
Anatolia, Türkiye. Data: SIO, NOAA, U.S. Navy, NGA,
GEBCO, Image Landsat/Copernicus, 26 April 2023) was
used to create a larger scaled hazard map.

Volcflow

We primarily simulated pyroclastic flows using Volcflow's
single-fluid version (due to its simplicity and general pur-
pose compared to the two-layer version), developed by
Kelfoun and Druitt (2005). VolcFlow (Kelfoun and Druitt
2005) is a simulation tool that models isothermal geophys-
ical flows on a volcano's digital elevation model (DEM).
As Volcflow creates flow paths on DEM, which presents
topographic data, we used the 30 m (ASTER GDEM) and
12.5 m (Alos Palsar) resolution's DEM of Mt Hasan. High-
precision simulation needs a more detailed DEM, but it is
a much more time-consuming process. That is why the first
models were realised using 30 m resolution DEM data,
followed by a more precise database.

This Eulerian code working under Matlab (MATLAB
version: 9.5.0.944444 -R2018b- The MathWorks Inc)
uses a depth-averaged approximation, serving multiple
purposes such as revealing pyroclastic flow behavior, and
creating hazard maps. VolcFlow can consider various
behaviors including frictional (with one or two friction
angles), viscous, Bingham, and Voellmy. It can also incor-
porate user-defined behaviors. More information is found
at the following: https://lmv.uca.fr/volcflow/.
<table><caption>**Table 1** ESP values for Volcflow modelling</caption><tr><td>Cohesion (Pa)</td><td>2000–5000</td></tr><tr><td>Plume height (km)</td><td>0–10</td></tr><tr><td>Run time (s)</td><td>300–600</td></tr><tr><td>Volume (km³)</td><td>0.3–10</td></tr><tr><td>Particle density (kg/m³)</td><td>2400</td></tr><tr><td>Concentrated flow density (kg/m³)</td><td>1600</td></tr></table>

The basic eruption source parameters (ESP) used in the modelling are given in Table 1. When selecting the ESP values, literature data were taken into consideration (e.g., Kelfoun and Druitt 2005; Kelfoun et al. 2017; Kelfoun 2017; Gueugneau et al. 2020). The simulation videos are available in “AVI” format and can be found in the Supplementary Information. BHD is almost completely covered by the block-and-ash flow deposits (BAF). Meanwhile, BAF is locally present on SHD. In addition, pumiceous pyroclastic flows and lahars are also encountered in the volcanological history of Mt Hasan. For that reason, various types of pyroclastic density currents (PDCs) were modelled using VolcFlow. These include the following: (1) PDC models with no plume formation, (2) PDCs formed by column collapse with low heights (e.g., 1–3 km), (3) PDCs formed by column collapses with heights of 10 km. In Volcflow runs, the cohesion (i.e., yield stress) values were generally given as 5000 pascals. Besides, we also input the cohesion values of 2000 and 3000 pascals to model the dilute PDCs.

## TephraProb

TephraProb generates scenario-based probabilistic hazard assessments based on tephra accumulation on the ground (Biass et al. 2016). It was developed by Biass et al. (2016) based on the Tephra2 advection–diffusion model of Bonadonna et al. (2005). We used this open-source Matlab toolbox to generate the Mt Hasan eruption scenarios.

In Tephra2, the advection–diffusion equation mainly considers the atmospheric conditions, grain size distribution (TGSD), and eruption source parameters (ESP). TephraProb initially asks for basic inputs such as a wind dataset and a grid (to determine the boundaries of the maximum possible spread and the modelling accuracy). For most runs the grid resolution was set to 5000 × 5000 m. Besides, we obtained wind profiles for the period between 2014 and 2019 from NOAA NCEP/NCAR Reanalysis 1 database (Kalnay et al. 1996).

We considered a normal distribution between the two end-members of each ESP for sampling. ESPs and models were calibrated using approximately 950 simulations corresponding to our 104 runs of TephraProb. We varied the plume height (m asl), TGSD, total eruption mass, and source area coordinates for various scenarios. We present the ESP values that we use as variables for TephraProb in Table 2. The identified ESP are given in the relevant figures. We then conducted approximately 1500 simulations for various plume heights and presented the results in Fig. 9. The maximum eruptible mass represented by a sub-Plinian plume eruption at Vesuvius is $10^{11}$ kg (Cioni et al. 2003). Additionally, Rosi et al. (1993) considered a total mass of $10^{10}–10^{11}$ kg. Moreover, Andronico et al. (2008) propose a $10^9$ kg eruptive mass for the eruption of low-height plumes of Etna. In our study, for sub-Plinian plumes (min total mass and max total mass) $10^9–10^{11}$ was chosen. Also, Carey and Sigurdsson (1989) reported in their compilation while examining Plinian eruption intensities that the plume height was 20 km and above and that the total mass amount varied between $10^{10}$ and $10^{14}$ kg depending on the eruption. So based on these data, a total mass of $10^{11}–10^{13}$ kg was chosen for the Plinian eruptions.

For Plinian and sub-Plinian TGSD values, $-6 \phi + 10 \phi$ (in their Fig. 8—Janebo et al. 2018) was used for the recent eruptions of Hekla volcano; $-10 \phi + 10 \phi$ (Johnston et al. 2012) for Minoan eruptions of Santorini; $-4 \phi + 10 \phi$ (Bonadonna et al. 2002) was used for deposits related to dome collapse modellings. In many

<table><caption>**Table 2** ESP values for tephra fall modelling</caption><thead><tr><th></th><th>Sub-Plinian</th><th>Plinian</th><th>Plinian (vent derived-Co-PDC)</th></tr></thead><tbody><tr><td>Plume height (km)</td><td>5–20</td><td>20–25</td><td>&gt; 25</td></tr><tr><td>Erupted mass min–max (kg)</td><td>$10^9–10^{11}$</td><td>$10^9–10^{11}$</td><td>$10^{11}–10^{13}$</td></tr><tr><td>TGSD range (phi)</td><td>−6 + 6; −7 + 2</td><td>−6 + 6; −7 + 2</td><td>−6 + 6; +1 + 6</td></tr><tr><td>Aggregation coefficient</td><td>0.3–0.7</td><td>0.3–0.7</td><td>0.3–0.7</td></tr><tr><td>Lithic density (kg/m³)</td><td>2500</td><td>2500</td><td>2500</td></tr><tr><td>Pumice density (kg/m³)</td><td>750</td><td>750</td><td>1000</td></tr><tr><td>Diffusion coefficient (m²/s)</td><td>900</td><td>900</td><td>900</td></tr><tr><td>Eruption duration (h) intervals</td><td>1–4; 4–6; 6–24</td><td>1–4; 4–6; 6–24</td><td>1–4; 4–6; 6–24</td></tr></tbody></table>

<figure><img src="image_6.png" /></figure>
other studies, the coarsest and finest grain size ranges were used. In our study, we generally used TGSD in the range of – 6 phi- + 6 phi for all sub-Plinian and Plinian plumes including the that of > 25-km plumes. In addition, especially for plumes > 25 km high, the grain size range of + 1phi- + 6 phi was also used. Such fine grain size range is also reported as Ultrafine ash of Co-PDC plumes (+ 3.5 phi- + 6 phi) by Engwell and Eychenne (2016). We conducted TephraProbe runs while adjusting the eruption duration values to 1–4, 4–6, and 6–24 h (see SI-figures).

In the end, we produced probability maps and probabilistic isomass maps derived from our defined ESP values. Probability maps establish a defined threshold for tephra accumulation (kg/m²) to delineate the associated spatial probability of exceedance (Biass et al. 2016). This is based on the conditional probability of the occurrence of the specified eruption scenario. Furthermore, probabilistic isomass maps establish a threshold to indicate typical tephra accumulation based on the probability of a related hazardous event (Biass et al. 2016).

## Results

### Morphological observations

Mount Hasan is a double-peaked volcano (BHD and SHD) built on a nearly flat plateau at approximately 1000 m asl. (Aydar 1992; Aydar and Gourgaud 1998). The present-day volcano, the Neovolcano phase, consists mainly of lava domes and related block and ash flows. BHD is almost wholly covered with block-and-ash-flow deposits (Figs. 1 and 2, SI-Fig. 1), while the flanks of SHD represent numerous lava domes and dome flows (Figs. 1 and 2). The regional Tuzgölü fault cuts the N-NE base of Mt Hasan. A Sentinel satellite image (Fig. 2a) and lava-pyroclastic facies (Fig. 2b) sketching of Mt Hasan are represented in Fig. 2. Young volcanics appear to be predominantly in pyroclastic facies. The lava flows, deeply incised valleys, and faults are well seen on the HD-DEM (Fig. 3a). The pyroclastics are mainly the BAF Deposits covering the whole BHD and extending toward the south of SHD (SI-Fig. 1). The landscape represents hummocky surfaces at the northern foot, corresponding to

<figure><img src="image_7.png" /><figcaption>Fig. 3 a DEM of Mt Hasan, b Slope map, c Drainage map</figcaption></figure>
debris avalanche deposits and associated tephra fall deposits (SI-Fig. 1).

The slope map shows that Mt Hasan rises on a plain (Fig. 3b). The steep cliffs appear mainly on the edges of the lava flows and faults. On the other hand, the steep (> 25°) and very steep slopes (> 30°) are encountered from an altitude of approximately 2000 m. The max slope value reaches 50° near the summit on the BHD terminal cone and is even close to vertical in places. Although the slope values are > 25° on SHD, some blue colors on the slope map correspond anomalously to nearly flat sectors toward the summit within the avalanche caldera. While creating the stream map (Fig. 3c), we added second-order drainage to the first-order drainage system to show any possible topographic controls on volcanic flows. The drainage network is densely developed on pyroclastic units outcropped on the slopes, especially on the BHD. However, it develops only on the inter-dome paths on the SHD flanks with many lava domes.

## Pyroclastic flow simulations

We present some of those simulations in video format in SI. For each model run, we changed the coordinates of flow initiation, its volume and height. Our modelling shows that a pyroclastic flow from BHD with a volume of 0.3 km³ and cohesion coefficient of 5000 Pa, is channelled mainly towards the north and west of the volcano, following the drainage patterns (Fig. 4). PDC use the channels carved in the pyroclastics and between the remnants of the older

lavas and deposit in the plain. They exhibit a pattern of thin deposits on steep slopes and thick deposits on low slopes. The thicknesses reach up to 10 m on the lower slopes. However, on the volcano's upper slopes, the thickness is very low, around 1 m. The PDC descending towards the south uses the high slope between the two summits, follows the drainage paths between the lava flows, and is deposited in a nearly flat area.

The PDC will also be deposited at the northern and western foot of the BHD (Fig. 4). PDCs originating from the BHD summit area reach the relatively flat topography at the base of the volcano due to channeling into the valleys on the volcano (Fig. 4). Similarly, we also applied smaller volume (0.085 km³) modelling of the SHD summit (Fig. 5). Flow patterns over the SHD indicate that flows are largely blocked or directed by lava domes and flows. Two main flow units pass through these natural barriers, mainly to the NNW and the ESE. While the NNW flow descends to the Helvadere settlement using the valleys between the lava flows, it is directed towards Ulkukışla and Altunhisar in the ESE direction. The branch descending to the south, where fewer lava domes are present, between two terminal cones, also shows a thick deposition in the lowlands around Uluören and Karakapı villages.

In addition, we simulated PDC by collapsing a 10 km high column for an eruption with a volume of 5 km³ and a duration of 300 s. The products of such an eruption mantled both terminal cones (Fig. 6). Generally, the deposition is minimal in the upper parts of deep valleys, where the

<figure><img src="image_8.png" /><figcaption>**Fig. 4** VolcFlow run for a BHD summital eruption with 0.3 km³ of total mass. ESP values are shown in the figure. Plan view of the extension of flow units on DEM. 3D views of the run from the west and south</figcaption></figure>
<figure><img src="image_9.png" /><figcaption>**Fig. 5** VolcFlow run for a SHD summit eruption with 0.086 km³ of total mass. ESP values are shown in the figure. Plan view of the extension of flow units on DEM. 3D views of the run from the north and south</figcaption></figure>

slope becomes steeper. The deposition thickens at the volcano's base. In this model, the relatively voluminous PDC that moved towards the west of the volcano covered the villages in the region and came very close to the Aksaray Organized Industrial Zone.

Another one is from the Western slope of the BHD. We simulated two different ESP values, one with a larger volume (150 × 10⁶ m³) with a yield stress value of 3000 Pa and the other by reducing the volume to 30 × 10⁶ m³ and cohesion to 2000 Pa. We chose the fumarole zone at the summit as the source area for these models (Fig. 7). In the higher volume model, we considered that the volcano would be covered with snow during the winter months, thus reducing cohesion and exhibiting more fluid behavior. Its flow behavior shows it reaches the lower slopes faster and more massively without being much different from other PDCs. In the lower volume model, we present a possible phreatic explosion and a possible mud flow. We ignore the possibility of slope instability in this sector. The ancient caldera border formed a lava barrier that significantly influenced the flow. Some of the flow could not pass through it, resulting in a thinner flow towards the south. The important part is that it cannot fully reach the base and remains at approximately 1100 m asl. However, the flow affects villages on the pathway, such as Dikmen and Gözlükuyu.

## Tephra fall modelling

To effectively assess hazards related to tephra accumulation, it is essential to develop eruption scenarios based in a volcano's history. Key parameters to analyze include winds, plume height, erupted mass, eruption duration, and grain size distribution.

We present the wind speed and dominant directions affecting Mt Hasan volcano in Fig. 8. The dominant and stronger wind directions to the east prevail up to 20 km. The wind reaches its max speed around 10–12 km height, troposphere-stratosphere boundary; then the speed decreases in the stratosphere toward 20 km high. Above 20 km in the stratosphere, westward wind directions are observed. Between 20 and 30 km over Central Anatolia, wind speed increases again without a significant change of direction. Westerly winds are much stronger than other provenance, with 40 m/s max wind speed.

To evaluate tephra fall hazards, we developed probabilistic maps depicting tephra accumulation probabilities, spanning from 0.01 to 1000 kg/m². Additionally, we constructed probabilistic isomass maps illustrating the percentage distributions of tephra accumulation for the same scenarios.

Tephra distribution scenarios for sub-Plinian and Plinian eruptions with varying column height and ESP values were applied to Mt Hasan. In numerical simulations, we created
<figure><img src="image_10.png" /><figcaption>**Fig. 6** VolcFlow run for a BHD summital eruption with 5 km³ of total mass. ESP values are shown in the figure</figcaption></figure>

<figure><img src="image_11.png" /><figcaption>**Fig. 7** VolcFlow runs for less cohesive flows to simulate a mass flow from the BHD summit. ESP values are shown in the figure</figcaption></figure>

<figure><img src="image_12.png" /></figure>
<figure><img src="image_13.png" /><figcaption>**Fig. 8** Wind data for latitude: 38 and longitude: 34. a Rose diagram of wind directions with wind speed. b Wind velocity profile with height. c Wind direction changes with height</figcaption></figure>

probability maps and isomass maps for column heights of 5–10, 10–15, 15–20, 20–25, and 25–30 km asl using all-year options. Seasonal changes in wind direction and tephra dispersal were also monitored. First, we set a TGSD in the range of –6 phi + 6 phi, the eruption duration to 4–6 h, and the eruptive mass to 10⁹–10¹¹ kg for sub-Plinian plume heights modelings, 10¹¹–10¹³ kg for Plinian plume heights modelings. The BHD summit was selected as the eruption point (Fig. 9). Figure 9 illustrates the probability maps for a mass accumulation of 0.01 kg/m², along with isomass maps at a 10% probability threshold for all plume heights utilized in the modeling separately.

In our presentation, we report the lowest quantity modelled along with its probabilities of regional dispersal and the lowest probabilistic isomass percentage of 10% as shown in Fig. 9. All other probabilities of accumulation related to all plume heights, ranging from 0.01 to 1000 kg/m², as well as probabilistic isomass maps from 10 to 90% related to tephra accumulation, can be found in SI-Fig. 3.

When the plume height is 5–10 km asl, the plume will be directed mainly to the east, and to a lesser extent to the south-southeast, and north-northeast according to

the prevailing wind direction. 0.01 kg/m² tephra will be deposited in cities such as Niğde, Ereğli, Aksaray, and Nevşehir with a probability of 10–20%. In general, tephra will be deposited on the main cone and in its immediate vicinity with a probability of more than 40%.

There is a 40–60% probability that up to 10 kg/m² of volcanic ash will be deposited on the eastern and southern slopes of the SHD (SI-Fig. 3). This would occur within a distance of 5–15 km from the source. When the tephra plume disperses approximately 80 km towards the south-east, there is a 10% probability that 0.01 kg/m² of tephra accumulates on the ground. With a 10% probability, it can reach as far as 150 km towards the Mediterranean Sea.

Aksaray city will experience 0.01 kg/m² of ash falling with 10–20% of probability. Furthermore, the ash will be transported up to 100 km in the direction NNE, partly influencing the Salt Lake. in the NNE direction, and with a probability of 30–40%, it will be deposited in the direction of Ihlara and Günzelyurt. Tephra accumulations ranging from 0.01 to 10 kg/m² will also be spread within these values (SI-Fig. 3).
<figure><img src="image_14.png" /><figcaption>**Fig. 9** TephraProb modelling of Mt Hasan summit eruption with probability of 0.01 kg/m² tephra accumulation (**a**, **c**, **e**, **g**) and possible tephra deposition (**b**, **d**, **f**, **h**) (for **a**–**b**: 5–10 km plume height, **c**–**d**: 10–15 km plume height, **e**–**f**: 15–20 km plume height, **g**–**h**: 20–25 km plume height, **i**–**j**: 25–30 km plume height. The intervals' probability thresholds and deposition values are displayed in contours and different colors; refer to the legend. All other outputs of probabilities are available in SI-Fig. 3</figcaption></figure>

<figure><img src="image_15.png" /></figure>
For a column height of 10–15 km, a maximum of 100 kg/m² tephra fall is deposited in a minimal area on the NNE slope of the SHD (SI-Fig. 3). Tephra is concentrated around the vent with an 80% probability (Fig. 9). In general, it is seen that tephra dispersal can occur in the N, NE, and E directions. The probability of 0.01 kg/m² tephra accumulation in a large city like Kayseri, with a population of over 1 million, is 30%. Additionally, 0.1 kg/m² tephra accumulation with 30–40% of probability is possible in the Nevşehir and Cappadocia regions (SI-Fig. 3). The impact area includes densely populated settlements since the plume spreads in the northeast.

When moving from the troposphere to the stratosphere with a column height of 15–20 km, tephra dispersal probability distances reach around 400 km from the vent, in N-NE-E and, S-SE directions. In particular, with 10–20% probability, 0.01 kg/m² tephra accumulates in major cities like Adana, Kayseri. Close to the source area, there is a 90% probability. On the other hand, there is a 30% probability of deposition of 0.1 kg/m² tephra in the city of Kayseri (SI-Fig. 3).

When the column height exceeds 20 km, the dominant wind direction throughout the year is N-NE, and the tephra scattering is generally towards the Black Sea direction. The probability of 0.01 kg/m² tephra accumulation is expected in the sector up to the city of Çorum, located 275 km NNE. Tephra dispersion affected all Central Anatolian settlements (Fig. 9).

Values as high as 250 kg/m² can be observed in areas very close to the source (SI-Fig. 3).

At 25–30 km column height, with increased eruption mass (10¹¹–10¹³ kg), 1000 kg/m² tephra fall occurs on and around the source. Twenty kilometers in the NE direction and 50 km in the SE direction are under 100 kg/m² threat (SI-Fig. 3). However, while the probability is 90% in the NE direction, it decreases to 40% in the SE direction. 0.01 kg/m² tephra dispersal seriously affects Eastern and Northeastern Anatolia, and its storage probability in the region up to Lake Van is between 30 and 40% (Fig. 9). There is a 10% probability that 0.1–1 kg/m² of tephra will accumulate on the shores of Lake Van, whereas there is a 90% probability that 1000 kg/m² of tephra will be deposited on the volcano. Additionally, although no locally or regionally distributed Co-PDC tephra was detected among the past eruption products of Mt Hasan, in one possible scenario, we modelled an eruption using a grain size range of +1 phi +6 phi, an eruption mass of 10¹¹–10¹³ kg, an eruption duration of 4–6 h (SI-Fig. 4). Our Co-PDC tephra fall modelling was focused solely on fine and very fine grain size criteria, without considering plume formation. The model makes it possible to deposit 1000 kg/m² of tephra from Mt Hasan towards NE-E, approximately 75 km. While the probability is 90% in the proximal regions of the volcano, this probability drops to

40% around Yeşilhisar and Yahyalı in NE. Likewise, high tephra accumulation values such as 500 kg/m² are also seen as regionally effective. The probability of deposition, which is 40%, especially in the east towards the Taurus Mountains, is around 90% in areas close to the volcano. The 0.01 kg/m² tephra accumulation probability shows a spread covering almost the entire Central Asian region.

We also simulate the 30–40 km high vent-derived plume model, with the –6 phi +6 phi grain size range, using an eruption mass of 10¹¹–10¹³ kg (SI-Fig. 5). It shows that the plume and tephra deposition is directed towards the east, and 1–10 kg/m² tephra deposition can be observed in the eastern regions of Türkiye.

As it is the most significant tephra fall activity on Mt Hasan, we wanted to reproduce the Belbaşhanı eruption. Although these deposits were first described by Aydar (1992) and Aydar and Gourgaud (1998), they were named as Belbaşhanı Pumices by Kuzucuoğlu et al (2020). This eruption, which is approximately 350–400 Ka old, was also studied by Özsoy et al. (2024). Those fallout deposits outcropped between SHD and Keçiboyduran volcano. In field studies, we could not find a horizon layer allowing us to correlate the outcrops/layers because of the excessive reworking and cover, so the isopleth and isopach maps were not meaningful. Besides, Özsoy et al. (2024) stated that they could make these correlations and provided the relevant sketchings. Even though it is ancient and does not provide any information about future volcanic hazards, we modelled it because it is within the behavior of the volcano and is the only important tephra fall product. In this model, we used the parameters –7 +2 phi grain size range, 4 h eruption duration, and 10⁹–10¹⁰ kg eruption mass (SI-Fig. 6). We accepted the farthest exposure distances as the envelope of the products. These products show a maximum dispersal (outcrop) of 17 km downwind and 7 km crosswind in the NE direction in the field. In the SE direction, it goes for a maximum of 10 km. Geologically, no regional spread was observed from this eruption. Using downwind, crosswind, and grain size values, we estimated the height of the plume to be approximately 18 km, according to Carey and Sparks (1986) calculation provided in the TephraProb Matlab Toolbox package. This height may be considered the minimum value as we do not have a complete plume geometry based on grain size distribution. Plume development is generally NE-oriented but less likely to be SE-oriented. According to Isomass contour probabilities, for a plume height of 10–15 km, tephra fall is compatible with its actual deposition with a 50% probability (SI-Fig. 7). As the plume height increases, its regional spread naturally increases. The tephra dispersal from the hypothetical 20–25 km column height (above sea level) affects the entire Cappadocia region, and large cities such as Kayseri and Aksaray are significantly affected, although we have no record in the field works.
Discussion

Mt Hasan was active during the Holocene period (8.97 ±0.64 Schmitt et al. 2014). In addition, the seismic crisis that occurred around Obruk village, located approximately 18 km SE from the BHD summit, near Mt Hasan, affected the fumarole activities at the Mt Hasan summit, causing severe increases in H₂S, CO₂, the temperature of fumaroles, and Radon concentrations (Aydar et al. 2021; Diker et al. 2022; Ulusoy et al. 2022). Aydar et al. (2021) attributed this hydro-logical response to seismic swarm to non-magmatic unrest, which increased the risk of phreatic eruption, similar to the Bandai-san eruption described by Yamamoto et al. (1999). Nonmagmatic sectoral collapse of volcanoes is challenging to predict and may result from shallow hydrothermal systems (Reid 2004). We modelled the PDC that this eruption could form. Water-saturation of pyroclastic material increases its flow velocity (Roche et al. 2001). According to the model in which we limit the yield stress (cohesion) to 3000 and 2000 pascals (Fig. 7), low-volume PDC will descend approxi- mately 12 km downhill, channelled into valleys, and affect the villages on their way.

In this study, we did not model a possible landslide similar to the Bandai-san-type eruption. Still, we foresee that the fumarole field, a weathered sector at the highly steep summit of Mt Hasan, could collapse.

Around 35,000 people live on and around Mt Hasan, with the population increasing during summer. Aksaray, home to approximately 320,000 residents, is located roughly 30 km to the northwest. There is no survey on this active/sub- active volcano. Our principal aim was to constitute espe- cially impact areas of a possible eruption on and around Mt Hasan Dag. According to its geological evolution and recorded events, we can expect some volcanic activities to have a significant impact in the near future. Besides, some hot or cold lahars may be generated. As we know, due to the steep slopes of BHD, which are covered by soft and unconsolidated block-and-ash-flow deposits (SI-Fig. 1), cold lahars are triggered after each heavy rainfall, especially on the western flank of BHD, affecting the road infrastructure.

We have grouped potential volcanic hazards related to Mt Hasan volcano into three different events: Low-Aspect Ratio (LAR) Pyroclastic Density Currents (PDC) and Mass Flows, High-Aspect Ratio (HAR) Pyroclastic Density Currents (PDC), and Tephra Fallouts.

LAR-PDC and mass flows

The aspect ratio is a morphological parameter that uses the thickness of deposits and travel distance (H/L). Low aspect cor- responds to high mobility of deposits along the pathway with less thickness. LAR-PDC and mass flows generally represent

lahars, debris flows, ash-flow tuffs, or ignimbrites. For LAR, which may occur due to high-volume eruption, when we make a 5 km³ flow model with a minimal volume increase and col- umn collapse, the flows cover the entire volcano and reach dis- tances of 15–20 km (Fig. 6). The increase in volume brings a high runout distance. The impact of pyroclastic density currents (PDCs) becomes more severe as the distance of their runout increases. So, Aksaray city, 30 km from Mt Hasan, will be threatened by a higher volume of PDC. Mt Hasan produced, in its past, several ignimbrites, debris avalanches, and lahars (Aydar and Bourguaud 1998; Kuzucuoğlu et al. 2020). Debris avalanches exhibit an aspect ratio (H/L:5/20000 m) of 2.5 × 10⁻⁴. How- ever, the furthest runout distance is around 20 km. The similar debris avalanche of Mount St. Helens on May 18, 1980, reached approximately 29 km (Glicken 1996).

HAR-PDC

Block-and-ash-flow deposits (BAF) are the most prevalent type of PDCs (Breard et al. 2023). The gravity and topography con- trol their mobility. Mitigating BAF hazards/risks requires accu- rately predicting affected areas and potential pathways (Breard et al. 2023). BAF cannot reach several km from the source area; besides, lahar (mud flows) can travel tens of km following val- leys. PDCs and mass flows are the deadliest volcanic products, with up to 90% of fatalities occurring within 30 km of the vol- cano (Auker et al. 2013). Three hundred fifty thousand peo- ple live within a 30 km radius of Mount Hasan. In particular, BHD is a PDC-producing volcano (SI-Fig. 1). However, in our models, the produced BAF deposits have a maximum 10–12 km runout. Morphologically, Mt Hasan is built on a flat plain with rude slopes reaching >45° (please refer to the slope map Fig. 3b). There are at least 11 settlements on and around Mt Hasan. In particular, almost all slopes of BHD are covered with BAF deposits. Remnants of collapsed domes are also found in the upslopes. While BHD is represented by dome emplacements and collapses in terms of behavior, SHD presents more dome- flows on its slopes. Of course, the exception is the sectoral col- lapse of SHD summit, which produces debris avalanches and related pumiceous falls and flows.

When we modelled low-volume PDCs with Volcflow, they moved on a track of 8–12 km at most and were depos- ited on the plains (Figs. 4, 5, and 7). The PDC are relatively thinner in the upper slopes. The plateau flatness and low slopes surrounding the volcano affect the mobility of PDC. When a circle with a radius of approximately 9 km is drawn from the summit, the part outside the circle has very low slopes. We already presented in Fig. 3 the slope map and drainage networks. When eruption volumes and supply rates are relatively low, the mobility of the flows also decreases, and they cannot travel long distances, but the villages on and around the volcano are on the PDC pathway.
We compiled and combined the PDC models of Mt Hasan, and we present a map (Fig. 10) that is based on the depositional thickness under topographic controls. This map indicates the potential impact areas in the event of a PDC generation. The colors are a function of the probable thickness of deposition. Areas with steep slopes are marked in blue, while plains are indicated in red. VolcFlow models have shown that as eruptive volume increases, PDCs reach farther and are deposited more in topographic lowlands illustrated with dark red areas and one of the simulations is presented in Fig. 6. The blue-green-yellow colors signify the shift from low impact potential to high. Areas with steep slopes and a thickness of less than 2 m are marked in blue. The mantling of topography is an expected behavior of flow

deposits. The green zones are some transitional zones from mantling to channelling. The dark red areas correspond to relatively flat areas where pyroclastic products might accumulate during high-volume eruptions if that is the case; however, they do not indicate the severity of the hazard. The significant agricultural and industrial activities, as well as the settlements (villages and towns, farms), are located in dark red areas. However, due to the steep slopes of the volcano, even relatively low-volume pyroclastic density currents (PDCs) can also extend to the plains below (see Fig. 10, SI-Figures, SI-videos). It is important to note that due to the high mobility of PDCs, they can channel into valleys and, during major eruptions, may be deposited in remote locations.

<figure><img src="image_16.png" /><figcaption>**Fig. 10** Compiled and combined PDC models of Mt Hasan and their probable impact zones. The figure considers the depositional thickness, topographical elements, human activity zones. The dark red areas represent the high impact zone related to thickness of deposited</figcaption></figure>

pyroclastics that will happen in case of high volume eruption, and the blue zone is a low-impact zone. Low-volume PDCs are deposited on slopes and reach the area where the slope flattens
## Tephra fall

Ash dispersal and fallout deposits may affect the proximal, medial and distal regions from the vent (Biass et al. 2024). Tephra falls may cause some physical damage to urban areas, such as roof collapses (Reyes-Hardy et al. 2024), aviation, and airports (Prata and Rose. 2015). Additionally, volcanic ash in the air harms the respiratory system (Aydar and Akkaş 2022). A 10 µg/m³ increase in air concentration of PM2.5 (particulate matter 2.5 microns) can increase cough, wheezing, dyspnea, and asthma attacks (Romieu et al. 1996). PM concentrations in the air for a short duration after a volcanic eruption can be much higher than regular outdoor air. For example, after the 2010 Eyjafjallajökull eruption, the 24-h mean PM10 concentration recorded was 1230 µg/m³ (Thorsteinsson et al. 2012), which is significantly higher than 15 µg/m³, the recommended typical outdoor air PM by WHO Air Quality Guidelines (2021). In our tephra fall models, amounts of tephra exceeding 1000 kg/m² can accumulate near the volcano, although it varies depending on the plume's height. In case of an eruption, tephra fall will affect some proximal, medial, and distal cities in Türkiye and the eastern countries.

The chosen eruptive mass of $1 \times 10^9–10^{11}$ kg in our tephra fall modelling is not enough to produce a plume exceeding 25 km. In a compilation work, Carey and Sigurdsson (1989) mention that a range of magnitudes for the Plinian phases alone (without flows and surges) is between $2 \times 10^{11}–8 \times 10^{13}$ kg. So we run the models for 25–30 km column height with the eruptive mass as $10^{11}–10^{13}$ kg.

Tephra fall deposits are subordinate comparing the PDC in the volcanic history of Mt Hasan. The volume of Mt Hasan and its products have been estimated as 354 km³ outcropping over an area of 760 km² (Aydar 1992; Aydar and Gourgaud 1998). However, Belbaşhanı fall deposits have a maximum $1–1.5$ km³ volume. Additionally, a wall painting discovered in the Neolithic settlement of Çatalhöyük exhibits a plume rising between two terminal cones of Mt Hasan with dotted patterns, probably corresponding to fallout deposits. It is worth noting that weak fallouts were deposited before the dome emplacements. Unquantifiable amounts of fallout deposits are related to the dome emplacements (Aydar 1992). However, we find the most important tephra fall deposits in the debris avalanche-related sequence. A similar development was seen in the St Helens May 1980 eruption (Glicken 1996). On May 18, 1980, the tephra plume lasted about 8 h, and the plume top ranged from 14 to 18 km high, approximately $1$ km³ (0.26 cubic miles) emitted ash volume (https://pubs.usgs.gov/fs/2000/fs036-00/). Ash fallout in Mt St Helens- 1980 caused significant problems in communities up to 630 km (Durant et al. 2009). Mt Hasan-Belbaşhanı Tephra Falls cannot be carried very far and may be observed at most 17 km from the volcano toward the

N-NE. We considered the farthest outcrops of the deposits as the envelopes of the deposits. When correlating this field data with Isomass contour maps produced using TephraProb, it becomes apparent that the modelled plume heights of 10–15 km and 15–20 km correspond probably to Belbaşhanı tephra distributions. This plume height is also confirmed by the plume height calculation method of Carey and Sparks (1986), which gave a height of 18 km. In other words, the relevant plume height confirms a sub-Plinian eruption. Besides, Özsoy et al. (2024) propose a plume height between 18 and 29 km with an average of 25 km. In Mt Hasan's case, ESP is similar to Mt St Helen's 1980 eruption but with less dispersed tephra. It may be a reason for the eruption duration and coarser TGSD. If there was no wind during the eruption, we should have seen the tephra fall deposit be much thicker. Still, even in the valley fill between SHD and Keçiboyduran volcano, it only reaches 10–15 m thick and thins rapidly towards the north. Another possibility is a very long eruption but a low eruption mass in weak wind conditions. According to the volumetric data and estimated plume height, Mt Hasan has not formed a plume that could have had a regional or global impact in the past. However, this does not mean that the plume will not form again. TephraProb models show that the plume will move mainly in the N-NE-SE-S directions.

In cases where TGSD is fine to very fine, according to our scenario, the Co-PDC plume and/or vent-derived plume (30–40 km height Plinian column) may reach the Central Asian regions despite no relevant information about such a previous production of Mt Hasan. Co-PDC falls related to BAF units have not been detected on Mt Hasan, probably due to reworking. Since the plumes that may form will be between a few hundred meters to a few kilometers (Engwell and Eychenne 2016), it is expected that they will have a relatively small dispersal pattern.

## Conclusion

1. Mt Hasan volcano is considered a dormant volcano that has exhibited several eruptions over the last 10,000 years. The fumarole activities around the summit area and recent eruptions (approx. 9000 BP and less than 6000 years old) make Mt Hasan a potentially dangerous volcano. A first volcanic potential impact map is proposed, drawn upon scenario-based assessments.

2. As the past volcanic history of the volcanoes gives some clues for a further eruption style, our scenario-based hazard assessment study shows that the future volcanic activities of Mt Hasan can be expected as a dome extrusion on the flanks with an eventual block-and-ash-flow generation. The impact of the eruption will be limited by the villages on the flanks because of the low mobility of such PDC. Or, an explosive eruption producing large,

<figure><img src="image_17.png" /></figure>
voluminous PDCs may also be expected. In this case, the volcano may start to collapse catastrophically, as it has happened in its history, and the large volume of PDC may reach Aksaray city.

3. According to the scenarios, a plume could be impactful in the main N-NE-E-SE directions under the influence of westerly winds. Depending on the height of this plume, it may affect Central Anatolian cities and even further east to a certain extent.

4. Flank instability and sectoral collapses are also expected volcanic disasters, primarily in the western part of the BHD summit.

5. Seismic and gas monitoring must be started on this unsurveyed volcano.

**Supplementary Information** The online version contains supplementary material available at https://doi.org/10.1007/s00445-025-01818-z.

**Acknowledgements** The authors thank Alessandro Taddini, the guest editor, and two anonymous reviewers who significantly contributed to the paper. We would also like to thank Karim KELFOUN for helping us use and implement VolcFlow during this study.

**Funding** Open access funding provided by the Scientific and Technological Research Council of Türkiye (TÜBİTAK). This study was supported by the TUBİTAK-BİDEB-2219 research program.

## Declarations

**Conflict of interest** The authors declare no competing interests.

**Open Access** This article is licensed under a Creative Commons Attribution 4.0 International License, which permits use, sharing, adaptation, distribution and reproduction in any medium or format, as long as you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons licence, and indicate if changes were made. The images or other third party material in this article are included in the article's Creative Commons licence, unless indicated otherwise in a credit line to the material. If material is not included in the article's Creative Commons licence and your intended use is not permitted by statutory regulation or exceeds the permitted use, you will need to obtain permission directly from the copyright holder. To view a copy of this licence, visit http://creativecommons.org/licenses/by/4.0/.

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