Detection of pyroclastic material and deformation of the lava dome in Mt. Sinabung with multi-temporal analysis (2010-2020)

The persistent eruptions of Mt. Sinabung resulted in the lava dome’s deformation and blanketed the surrounding area with pyroclastic material. This research focused on determining the changes in Mt. Sinabung during the prolonged eruptions from 2010-2020. A total of 22 volcanic ash samples were collected following a 1x1 km grid interval spread over from the East to South slope of Mt. Sinabung. The studied area is the most affected by the volcanic eruption. Digital elevation models from the shuttle radar topographic mission and sentinel-1 were utilized to monitor deformations of the lava dome and the distribution of pyroclastic material on Mt. Sinabung. Sentinel Application Platform and Google Earth Engine were used as the main tools in multi-temporal digital elevation model (DEM) data processing. The eruption of Mt. Sinabung from 2010 to 2020 changed the height from 2,460 m to 2,404.3 m and created a new crater (5.35 ha). The lava dome volume from 2010 to 2020 is about 2,308,041 m3 and has collapsed to produce pyroclastic material which deposits to the surrounding area of Mt. Sinabung during the eruption. The distribution of pyroclastic material increased from 2010 to 2019, covered up an area of 103.27 ha (2010), 846.48 ha (2013), 1,029.74 ha (2016), 1,235.97 ha (2017) and 1,463.62 ha (2019). The thickness of the pyroclastic material deposits at Mt. Sinabung until 2020 varied from 13,24 cm to 219 cm. The findings from this study can be used as a reference for observing topographic changes due to volcanic activities and drawing a mitigation and contingency plan for a volcanic disaster program in the active volcanic region of Indonesia.


Introduction
The eruption of Mount Sinabung has occurred periodically since 2010 and at the same time changes the status of Mount Sinabung from type 'B' mountain to type 'A' mountain [1].The persistent eruption of Mount Sinabung resulted in the deformation of the lava dome from initially conical to u-shaped (Figure 1).The pyroclastic material comes from a significant change in the 1306 (2024) 012022 IOP Publishing doi:10.1088/1755-1315/1306/1/012022 2 A B temperature of the lava when it arrives at the surface [2] and scattering from the raised lava dome during the eruption of Mount Sinabung.The pyroclastic material resulting from the eruption of Mount Sinabung buried several villages around Mount Sinabung.From that condition, a 7 km radius from the summit was designated as a dangerous zone by Indonesian government.Substantial topographic changes occurred due to the eruption of Mount Sinabung such as deposits of pyroclastic material and the deformation of the lava dome.Nowadays, remote sensing data generally facilitate observations of changes in the topography of volcanoes before and after the eruption.From there, we can easily approach a lot of data, such as radar sensors from the Sentinel-1 satellite and visual observations with the sentinel-2, Landsat 8.
East until South slopes are the areas where the most pyroclastic material is deposited on Mount Sinabung, and the deformation of the lava dome can be seen since the eruption in 2010.Observations, forecasting, and modeling of Mount Sinabung deformation in this study utilize geographic information systems.

Geological condition
Sinabung volcano is an active volcano located in Karo regency, North Sumatra, Indonesia (Figure 2).Sinabung volcano has a special condition, more than four-century in a dormant state, and for the first time, it erupted in 2010.A plate movement caused the Sinabung volcano eruption in Sumatera island, especially because of the convergence between Indo-Australia and Eurasia plates (Figure 3) [3] [4].Sinabung volcano erupted burying some villages with pyroclastic material until 5 km from the eruptive vent.Sinabung volcano hazards include pyroclastic falls (volcanic ash and rocks), pyroclastic streams or hot clouds, and lava flows [5].

Scientific Approach
This research uses interferometry analysis [6] to detect the deformation of the lava dome and elevation change in the Sinabung volcano.With it, we can calculate the volume of pyroclastic material that has erupted in the Sinabung volcano.Pyroclastic material deposits and the area of it analyzed with interpretation analysis [7].This research compares each data using temporal analysis with multi-image Satellite (Table 1).Raw data of SRTM will be resampled to calculate the value of each pixel by fitting a smooth curve based on the surrounding 16 pixels.This research improves the resolution of SRTM to 15 m to produce the smoothest image so that it can be compared equally between SRTM and Sentinel-1.

Sentinel-1
The interferometry analysis is based on the Sentinel-1 SLC data product (table 2).This research uses it to get the latest data on topographic conditions in the Sinabung volcano.Data collection with sentinel 1 needs to consider the geometry baseline, temporal baseline, view angle (descending or ascending phases), image coherence, and meteorological conditions around Sinabung volcano so that interferometry runs optimally and produces perfect digital elevation model data.
Sentinel-1 SLC (single look complex) has 12-day temporal data for each image, and the shorter temporal baseline will guarantee better coherence for interferometric pairs.The temporal baseline in the Sinabung volcano is important because the eruption was persistent, which changes the topography.Baseline geometry considers the distance between the images used in the range of 150-300 meters in order to minimize atmospheric effects, phase noise, and scattering decorrelation.Interferometric pairs must have the same angle, ascending or descending.The different angles will cause the opposite angle of foreshortening and layover effects on the terrain and will not have any coherence.Consider the cloud from the eruption of Sinabung volcano and other meteorological conditions usually cause loss of phase coherence [6].8 for Visible light (RGB), aerosol, Near Infrared (NIR), Short wave Infrared (SWIR), and Cirrus at 30 meters, thermal at 100 meters, and panchromatic at 15 meters [9].Sentinel-2 is a highresolution optical image with 12 bands with 10 to 20 meters resolution for NIR, and Visible light, 20 meters for SWIR, and 60 meters for coastal aerosol, water vapor, and cirrus [10].Data Landsat 8 for interpretation analysis using panchromatic, which is band eight composites with visible light, NIR, and SWIR.Sentinel-2 uses a composite of visible light, NIR, and SWIR, which are bands 2, 3, 4, 8, and 12.All of it is for enhancing the color Spectrum to get a greater image for analysis.

In-Situ Data
To improve data accuracy, we organized a field trip in March 2020.Dangerous conditions in the Sinabung volcano cause the intensity of eruption, so we limited the research area only from a 3 km to a 7 km radius from the eruptive vent.Total area covered 4,517 ha and there were 49 sample from East to South using a grid of 1x1 km (Figure 4).In the field we collected data such as elevation with Global Positioning System (GPS), thickness of pyroclastic layer, and landscape and environment condition, and temperature of pyroclastic layer.
We recorded coordinates and elevation with GPS at every site and crosscheck the data again with satellite images.The pyroclastic material thickness was measured until the upper surface of soil detected.We then dug it and searched for around 100 meters from the sample point with the best spot.Data pyroclastic material thickness will be processed using the kriging method to calculate and predict the thickness around every sample point in the research area.

Deformation of sinabung
Sinabung volcano is considered as one of the most active volcanoes in Indonesia, the summit geographically located at the latitude 3°10'16,7" N and longitude 98°23' 24,66" E. On September 7, 2010, the Sinabung volcano ejected ash columns 5 km into the air.The persistent eruption of the Sinabung volcano until 2020 changed the surrounding area of Sinabung and the height of the volcano decreased from 2,460 m to 2,404.3 m (Figure 5).The collapse of lava dome with approximately 1.9 x 10 6 m 3 volcanic material resulted pyroclastic density currents (PDS) and these materials deposited at the upstream of the Lau Borus River.The river was dammed and formed a lake-like puddle with an area of 9,84 ha (Figure 6).The new lake detects with Sentinel-2 (image processing with short wave infrared composite between band 4, 8A, and, 12) [11].Yellow polygon is area of new lakes formed in 2017.The eruption of the Sinabung volcano also created a new summit crater (5.35 ha).It was destroyed by lava extruded rapidly (Figure 7).this change is in line with the deformation of the lava dome, which 2,308,041.992m 3 has collapsed to produce pyroclastic material which deposits to the surrounding area of Sinabung volcano during an eruption.We estimated this volume by calculating radar data from the specific altitude of the lava dome during the dormancy period and after the persistent eruption (2020).(Figure 8) Green area is the lava dome detected with SRTM (after resampling it to 0,00013 arc degrees) in the dormancy period.Red Area is the lava dome condition after persistent and explosive eruption until 2020 and detected with sentinel-1 (0.00013 arc degrees).Because the distribution of pyroclastic material around Sinabung volcano causes elevation changes, this is proven by the field checks.We carried out at 22 points where pyroclastic material deposits were found on the surface and correlated with the radar data (Figure 9).

Pyroclastic Material Deposit
Through the condition of the eruption, we used geographic information system data to detect the pyroclastic material deposit.Using some optical satellites made this possible.This research used a combination of data from Landsat and Sentinel-2.The Landsat data from the dormancy period until 2015 and the Sentinel-2 data from 2015 until the present.We formed the deposit area by keeping track of the pyroclastic material deposit with interpretation analysis and correlation with in-situ data.The distribution of pyroclastic material increased each year (Figure 10 From our field survey, we observed the pyroclastic material thickness varied from 13,24 cm to 219 cm.At some point, we could measure it instantly cause the infiltration condition created some erosion path [12].This data is obtained after processing with the kriging method and strengthened by field data (Figure 11).From our observation, we found the pyroclastic deposit has some layers from the eruption each year.East to South is the area where the most pyroclastic material is deposited on the Sinabung volcano [13]

Conclusion
Mount Sinabung's volcanic ash is mainly spread on the eastern to southern slopes with an area ranging from 103.27 to 1463.62 ha with a thickness of 13.24 cm to 219 cm.Deformation that occurred on Mt.Sinabung consisted of formation lava dome (2,308,041.992m 3 has erupted), changes in mountain height (5-30 m), formation of a new lake (9,84 ha) and a new summit crater (5.35 ha).The work presented here verify that high quality remote sensing data on monitoring volcanic activities estimate landscape changes that occur before, during and aftermath of the eruption with space and time.

Figure 1 .
Figure 1.(a) Changes in the panorama of the peak of Mount Sinabung due to the massive eruption of February 19, 2018, immortalized by volcanology and Geological Hazard Mitigation (CVGHM) (b) Sinabung peak was taken during sampling in 2020.

Figure 2 .
Figure 2. Administration Map of the Sinabung volcano.

Figure 3 .
Figure 3. Indo Australian and Eurasia Plate movements were marked by an earthquake in Sumatra island [3].

Figure 4 .
Figure 4. Sample point Map with radius 3-7 km from the center of eruption Sinabung volcano.

7 Figure 5 .
Figure 5. (a) DEM at Sinabung Volcano while in Dormancy state (b) DEM at Sinabung volcano after persistent eruption until 2020.From both of these images, we can check the deformation at the cone of the Sinabung volcano.

Figure 6 .
Figure 6.(a) Sentinel-2 image (SWIR analysis) detects a new lake in the east of Sinabung volcano with a 9,84 ha area, (b) new lake water depth test (around 80-100 cm), (c) new lake landscape in the East of the Sinabung volcano.

Figure 7 .
Figure 7. New Crater in Sinabung volcano with a 5.35 ha area.

Figure 8 . 10 Figure 9 .
Figure 8.In lava dome deformation modeling, green show dormancy period condition, and red show lava dome after a persistent eruption.

Table 1 .
The information data used in this research.

Table 2 .
[8]tinel-1 data.Google earth engine is an open-source database for satellite imagery.Accessible multi-data and time series with simple and rapid is the advantage of the google earth engine.Interferometry, until the present, is not supported in the google earth engine because the model data available is based on 2D gridded raster bands[8].This research uses the google earth engine platform to process data Landsat 8 for interpretation analysis until 2015 and sentinel-2 from 2015 until the present.Landsat 8 is an optical satellite with 11 bands and 16-day temporal granularity.Spatial resolution in Landsat