Changes in Anak Krakatau landscape after December 2018 eruption

Abstract

The south-western slope of Anak Krakatau collapsed after the eruption on December 22nd, 2018 and reshaped the volcanic island landscape. This work focused on determining the geomorphological features of Mt. Anak Krakatau before and after the eruption. A total of 71 lapilli and 17 volcanic ash samples were collected from Anak Krakatau and Panjang islands on February 23, 2019, and March 14, 2019. Sentinel-2 and Planet Scope images were utilized to monitor thermal activities and the changes of the coastlines. Google Earth Pro was capitalized to determine the rills and gullies formation. After the December 2018 eruption, the height of Anak Krakatau was reduced from 258 to 126 m and, about 76 x 106 m3 of materials were eroded to the sea. The eruption caused Anak Krakatau to be covered by unconsolidated volcanic materials. About 214 of rills (dimension of 380 to 851 m and 30 to 100 cm) and 35 of the gully features (length from 150 to 841 m and width from 0.5 to 13 m) run from the highest peak to the coastline. This work can serve as a reference for predicting potentially disastrous events such as Anak Krakatau, which shows growth and destruction can be observed using remote sensing techniques.

Detailed Mapping of Lava and Ash Deposits at Indonesian Volcanoes by Means of VHR PlanetScope Change Detection

“…Modelling of the tsunami shows a wave run-up of 10-23 m on the S, W, and NW coasts of Kecil [9], indicating the destruction of vegetation there and explaining the significantly lower dNDVI values in this area. Additionally, in the E of Anak Krakatau, the sharp decrease in the NDVI signal can be explained by the complete destruction of vegetation due to explosive eruptive activity [19].…”

“…Lava effusion and Strombolian activity continued into September 2018, whereby an increase in eruptive activity was observed [41]. As a result, steady lava effusion flowed into the sea off the S coast of Anak Krakatau, creating 12.09 ha of new land [19]. In October and November 2018, lava flows also occurred more frequently in the SW of the island.…”

“…In total, 437 people were killed and over 31,000 were injured [42]. The eruption also resulted in large-scale tephra deposition on the surrounding islands [10,19].…”

“…In addition to the frequently used infrared (IR) (e.g., [14][15][16]) and synthetic aperture radar (SAR) (e.g., [10,17]) data, optical satellite data are also useful for the monitoring of active volcanoes. Very high-resolution (VHR) optical systems have been used to map ash and tephra deposits [18], lava flows [19], pyroclastic flows, and lahars [20,21] at volcanoes. Lower-resolution optical imagery (e.g., Sentinel-2, Landsat-7/-8) (10-30 m) have also been successfully used to detect volcanic hazards (e.g., [22][23][24]).…”

“…Aldeghi et al [18] successfully used PlanetScope data to determine the spatial extent of ash and tephra deposits following an eruption of Fuego, Guatemala. Other studies used PlanetScope data exclusively for visual analysis of geomorphological changes at Krakatau, Indonesia, [19] or to generate multi-temporal digital elevation models (DEMs) from which lava flow deposits at Nabro, Eritrea, could be derived [14].…”