Deformation and instability at Merapi dome identified by high resolution camera

After phreatic eruptions in May and June 2018, a new dome continuously grows and deforms at Merapi summit. The growth of the Merapi dome progressively causes over steepening, triggers gravitational instability, and then collapses, producing pyroclastic flow. These activities have been observed by our high-resolution camera. Here, we performed high resolution terrestrial photogrammetry to identify deformation and instability at the Merapi dome. The data were collected between 10 and 15 April 2019 by using Cannon EOS 60 D camera and equipped with 200 mm lens. The 200 mm tele lens is able to provide detail morphology and to identify deformation up to sub meter accuracy. The high-resolution images were processed by registering a slave image to a reference image, scaling the images, and applying pixel-tracking techniques. The technique is able to identify deformation of the Merapi dome. Results show a continuous deformation with mean displacement of ∼1m during that period. A strong deformation was identified at the south-eastern part of the dome with maximum displacement up to 5 m which might be associated with a dome collapse that produced pyroclastic flow on 10 April 2019. Based on our observation, we infer that the activities of dome growth and gravitational instability triggers dome collapse are recently dominant at Merapi volcano.