On October 26, 2021, the fourth expecition of the ICE-VOLC project began on the Rittmann and Melbourne volcanoes.

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The activities carried out on the Rittmann concerned:

Permanent seismic-acoustic station: during the XXXVII expedition, the data acquired from November 2019 were downloaded and the general conditions of the mechanical structure as well as the integrity and functionality of the power supply system were successfully verified. The GURALP 3T 120s speed sensor has been replaced with a Nanometrics Trillium 40s complete with wiring. A preparatory work was carried out at MZS for the commissioning of the sensor by centering the sensor masses at a temperature of -12 ° C, and assembling the connection cable between the sensor and the digitizer. Furthermore, the configuration regarding the format of the internal storage files has been changed to allow a more versatile and analysis of the acquired data.

Tephra sampling: some samples of deposits emerging on the walls of the Rittmann were carried out in conjunction with the maintenance activities of the seismic-acoustic station.

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The activities carried out on Melbourne concerned:

Temporary seismic station: A temporary seismic station called AURO was installed inside the Aurora-MC1 cave. In particular, a TRILLIUM Compact 120s broadband velocimetric sensor was buried at a depth of about 40 cm in the ground and about 2 meters from the LUNITEK ATLAS-6F digitizer. Examples of acquired signals are shown in Figure 3.

Installation of a data transmission system: A data transmission system with both WiFi technology and UHF radio band was installed, and various radio tests were performed from the top of Melbourne to the MZS base for data transfer acquired from both seismic and geochemical stations.

Geochemical station: The maintenance of the geochemical station was performed with the replacement of the faulty pump, probably starting from March 2021, the resynchronization of the RCT delayed by about 14 months. We proceeded to download the data and realign the dates and times of the records, repair the spectrometer, and a malfunctioning H2S sensor was identified.

Thermal measurements: A TinyTag temperature sensor was replaced at the MG2-Aurora geochemical station. The HOBO temperature sensors buried at 20 and 60 cm in the bottom room were removed and then repositioned after maintenance and data download.

Gas sampling: in collaboration with the MIMIC Project, gas sampling was carried out in the sites in the caves identified with the biologists (Aurora, MC3 and MC4).

Tephra Sampling: As far as Baker Rock High is concerned, the sampling of the surfacing tephra levels could not be performed due to a significant accumulation of snow on the wall. As an alternative, it was possible to drill the ice about 10 meters upstream of the wall itself in order to sample the aforementioned tephra levels. In addition, samplings of volcanic rocks outcropping near the Aurora, MC3 and MC4 caves were carried out. These two activities were carried out in collaboration with MIMIC.

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