ISMOSAV monitoring networks

Overview of monitoring networks

Local permanent network of ISMOSAV in cooperation with the Aristotle University of Thessaloniki, Hellenic Survey of Geology and Mineral Exploration (HSGME) Red Circles: Seismological stations  Blue Pins : GNSS stations Square: CO2 station Orange Circles: Thermal Stations

CO2 soil flux continuous monitoring

During a volcano reactivation, the gas and liquid phase which is a part of the new magma, arrive much faster to the surface, drastically changing the chemical composition of the hot gasses (fumaroles) and fluids (hot springs).

The most abundant magmatic gas phase, after the water, is the CO2. On a selected site, on Nea Kameni, has been installed a continuous monitoring CO2 soil flux station.

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Geophysical-Geochemical stations supported by ISMOSAV in Santorini. White Square: Carbon-dioxide station [CO2], Orange Circles: Temperature measurements stations

ISMOSAV manage to has in continuous function a CO2 soil flux monitoring station, installed on the Nea Kameni most active area.

The main flux values per day, recorded by this station during the complete monitored period, range between 5 and 50 ppm/sec, while the maximum recorded values do not exceed the 150 ppm/sec. These values are considered as characteristic for the repose period of the volcano.

The measurement of the CO2 soil flux is very important for volcanic monitoring.

High amounts of CO2 are released to the atmosphere from active volcanic areas not only during eruptions but also during quiescent periods. This volcanic CO2 discharge occurs from both active craters, as plumes and fumaroles, and the flanks of volcanic edifices, as diffuse soil emanations.

Therefore, the observation based on CO2 soil flux monitoring can be carried out at safe distance from active craters, which is particularly important during pre-eruptive and eruptive periods.

Among the different methods to measure the soil CO2 flux, we have chosen to use the accumulation chamber method or closed-chamber method. It is the best way to measure CO2 soil flux values of volcanological interest, as it does not require any corrective factor depending on soil characteristics.

CO2 soil flux monitoring station, installed on Nea Kameni

The instrument utilized consists of:

1. An accumulation chamber
2. An IR spectrophotometer Drager Polytron, to measure C CO2 in the 0 to 20,000 mmol/mol range3. A specialized data logger: WEST System’s Soil gas station.

The accumulation chamber

The accumulation chamber is lowered on to the ground for 3-4 minutes every hour, during this period the gas is continuously extracted from the chamber, sent to the IR spectrophotometer, and then injected again into the chamber. The latter is equipped with a mixing device in order to improve gas mixing. Values of CO2 inside the accumulation chamber are acquired by the data logger.

The chamber rim is designed to be set properly on the ground in order to eliminate the input of atmospheric air, which could cause significant errors, especially on windy days. The chamber is connected to the atmosphere through a very small hole on the top of the chamber to ensure that the pressure inside the chamber itself is always equal to the atmospheric value.

Carbon dioxide detector specification

DRAGER Polytron IR for carbon dioxide.

Working principles: Double beam IR Detector with solid state sensor compensated in temperature, without moving parts.

Full scale :Range  from 2000 ppm to 100% configurable by the operator.

Accuracy 3% of reading at 350 ppm

The Gas station

The gas station is a specialized data logger, which can read up to 24 analog signals and manage the flux measurement, lowering and lifting the accumulation chamber every hour.  The gas station is powered with a solar cell panel and a backup battery.  The instrument is designed to resist hard chemical attack, due to sulphur gases, typical of volcanic environments.  The acquired data are stored locally in a solid state flash memory and are transmitted to the master center with a radio telemetry system.

Maps of CO2 soil flux prominence to active faults and fractures acting as uprising routes of deep CO2-rich geothermal or magmatic gases and can be used to estimate the total diffuse CO2 output from the entire system. Moreover these maps allow selection of restricted areas where repeated measurements of COsoil flux can be carried out to investigate the temporal evolution of the system.

The installation site, on the top of “Georgios” dome at Nea Kameni islet, was selected after several soil flux mapping that we conducted with a portable carbon dioxide flux meter. This was the site with the maximum CO2 diffuse soil flux.

It has been observed that COsoil flux are affected by changes in pressure, as expected if gas transport takes place mainly through advection. Other meteorological parameters such as rain, soil and air temperature, and humidity may affect soil-gas concentrations and fluxes. Monitoring of CO2soil flux for volcanic surveillance must, therefore, include acquisition of meteorological data.  For this reason the continuous monitoring device is equipped with a barometric pressure gauge, a soil temperature probe and an air temperature gauge.

 

Seismic monitoring

Long-term  international experience in active volcanoes has shown that the most effective method of monitoring is seismic. It is based on the principle that magma, when it rises to the surface, causes micro-earthquakes, which can be recorded with great accuracy by seismographs of a specially designed local network. The exact location of the hypocenters of the micro-earthquakes and the determination of their possible migration makes possible to estimate the location of the rising magma on its way to the surface at all times, its rising velocity and its possible exit location long before the occurrence of the eruption. This is achieved by installing and operating a permanent seismic network with a sufficient number of seismographs located at selected points in the wider area of ​​volcanoes.

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Santorini's Seismological Network. Red triangles: Seismological Stations operated by ISMOSAV, blue triangles: Seismological Stations operated by Institute of Geodynamics, National Observatory of Athens, green triangles: Seismological Stations operated by Kapodistrian University of Athens

The real-time seismicity monitoring of the Santorini area is based on the operation of 10 permanent seismological stations (red triangles shown on the map), which have been originally installed with the support of EC and are currently operated by the Institute for the Study and MOnitoring of the SAntorini Volcano (ISMOSAV) in collaboration with the Seismological Station of the University of Thessaloniki. Additionally two other seismological stations (blue triangles on the map) operate in the island of Santorini by the Geodynamical Institute of National Observatory of Athens. Also, National and Kapodistrian University of Athens operates two more seismological stations (green triangles shown on map).

Snapshot of the THR6 seismological network of ISMOSAV installed at Akrotiri area

The whole set of data is digitized and transmitted via a digital antenna to the main building of ISMOSAV at the building block of the company IRIS on the road of Fira-Pirgos. Finally, the recorded data, which are one of the main tools for the correct and continuous monitoring of the volcano of Santorini are transmitted in the Central Seismological Station of the Geophysical Laboratory of Aristotle University of Thessaloniki, in real-time, using an ADSL internet connection. For safety reasons there is also a satellite transmission station installed at the location of the CMBO seismic station. In Thessaloniki, there is a continuous processing of seismological data, 24 hours per day, by the seismologists of the Geophysical Laboratory of AUTh (http://geophysics.geo.auth.gr/ss/station_index.html).

 

Thermal monitoring

Temperature is one of the physical parameters of a volcano that typically increases during reactivation periods. Thermal monitoring is therefore a necessary component of a complete monitoring system.

On Santorini, thermal monitoring includes:

Continuous recording of the Nea Kameni fumarolic temperature and the soil temperature on the CO2 flux measurement area is performed, as well as continuous temperature recording on the Palea Kameni (Ag. Nikolaos cove) hot spring.

Periodic temperature recordings (3-4 times per year) take place at the Nea Kameni (Afroessa cove) and Thira (Plaka, Athermi Christou) hot springs, as well as that of the deep well performed by H.S.G.M.E. on south Thira.

The thermal manifestations on Santorini are concentrated in two areas : the Kameni area and on Thira in the western margin of the prevolcanic metamorphic basement.

 

Nea Kameni fumes

 

Fumarolic activity is prsent only on the top of Nea Kameni island. Fumaroles are concentrated on the top and the east flank of Georgios dome, built up during the 1866-1870, and mainly at the eastern rim of two hydrothermal vents ("twin explosive funnel") formed in August 1940, during the volcanic activity of 1939-1940.

Fumarolic gasses have a temperature ranging from 60oC to 90oC, depending mainly from the altitude (the highest sites in altitude register the highest temperature values).

There are no stable sites or open vents where the maximum temperature values can be registered. The system is unstable, as fumarolic gasses outflow mainly through pyroclastic deposits. The maximum registered temperature on Nea Kameni fumaroles present a fluctuation of about 3oC (94oC ~ 97oC).

Many hot springs appear along the coasts of Palea and Nea Kameni. The two main ones are located along the active tectonic line of the Kameni islands, in the isthmus between Palea and Nea Kameni.The maximum recorded temperatures here are: 34oC for the hot fluids outflowing in the Afroessa cove of Nea Kameni and 38oC for the hot spring of Palea Kameni Agios Nikolaos cove. The 2~3oC fluctuations recorded are due to unstable weather conditions (season, wind, tide, currents).

A deep exploratory well (-220m) has been carried out on Palea Kameni close to the hot spring; aiming to study the hydrothermal system of the area. The maximum temperature recorded in it was 29oC in the depth of 8~10m.

On the island of Thira thermal manifestations are located on the western and southern margins of the pre-volcanic bedrock. Three main hot springs are found here: the Plaka (average temperature 33.6oC), Athermi Christou (average temperature 56oC) on the central-eastern coast of the caldera slopes and Vlihada (average temperature 33.2oC) hot spring on the southern coast of the island. All three hot springs outflow on the seashore.

A deep exploratory well drilled by HSGME in the area of Agia Anna in southern Thira, encounters a warm aquifer with a constant maximum temperature of 52.2ºC at a depth of 365 meters below sea level.

Ground Deformation monitoring

The Global Positioning System (GPS) is a space-based Global Navigation Satellite System (GNSS) which by using signals transmitted by GPS satellites, can calculate the positions of ground‐based receivers with high precision,making it possible to track the movement of points on the Earth's surface over time. GPS data provide important constraints on the underlying processes that lead to observed deformation, especially when used in combination with other data types. Volcanic deformation is often characterized by transient signals. Magma or hydrothermal fluids migrate beneath the volcanic edifice, causing inflation or deflation and sometimes culminating in an intrusion or eruption. The steep flanks of volcanoes are often unstable, leading to landslides and in some cases collapse of large sections of the edifice. GPS is very well‐suited to monitoring these types of deformation signals, and many of the world's volcanoes have GPS receivers installed for this purpose.

Since 2019 ISMOSAV has proceeded to the installation and establishment of a new modern geodetic network on the island of Santorini in order to monitor crustal deformation due to volcanic processes. The network consist of four (4) GNSS recievers which continuously collect and record data which are sent via the internet to the AUTh for their final processing. The data is sent using the protocol of anonymous file transfer (FTP) to the server of the research team of the School of Rural and Surveying Engineering of AUTh.

 

Location of the GNSS permanent stations of the ISMOSAV network in Santorini. SAWI station is kindly granted by METRICA company

The 4 geodetic stations of the new ISMOSAV network are of modern technology and make use of the global geodetic data reception systems, GPS, GLONASS, GALILEO and BEIDOU. Their complete characteristics are given in Table (1) such as the coordinates and the basic information about the technical characteristics and the mode of operation of each permanent station.

Station Name

Latitude

Longitude

Elevation (m)

Site Name

Receiver Type

Antenna

Data recording rate

Sattelite Systems

Communication

ΑFAL

36ο 27'

25ο 23'

196

Oia

Leica GRX1200GGpro

Leica

AR10

30 sec

GPS+Glonass

Dynamic IP

MANO

36ο 26'

25ο 20'

206

Thirasia

Leica GRX1200GGpro

Leica

AR10

30 sec

GPS+Glonass

Dynamic IP

SAWI

36ο 23'

25ο 26'

340

Pyrgos

Leica GR30

Leica

AR10

30 sec

GPS+Glonass+Galileo+ Beidou

Dynamic IP

SANT

36ο 26'

25ο 25'

370

Imerovigli

Leica GR10

Leica

AR10

30 sec

GPS+Glonass

Dynamic IP

 Table 1 Coordinates and basic information of the technical characteristics and the operation mode of each GNSS permanent station of the ISMOSAV network

 

The ability to remotely control the correct operation of each GNSS station led the Geodetic Deformation team to install a Raspberry Pi electronic device  at all ISMOSAV GNSS stations. The Raspberry Pi is an extremely small computer and is characterized by its efficiency and reliability. It was released in 2012, reaching today its new versions, the Raspberry Pi 3 and 4, which were supplied by ISMOSAV. It has a quad-core ARM CPU at 1.5GHz, 16 GB RAM, 4 USB 2.0 ports and another HDMI . Thus, it can be connected to a TV/monitor and standard peripherals, allowing internet browsing and remote data transfer control.

 

Antenna (left) of the GNSS-AFAL permanent station in Oia  and its receiver and its accessories (right) installed by ISMOSAV

In all modern high-tech networks for the monitoring of terrestrial deformation and especially for the high accuracy measurement of terrestrial deviations in the 3 dimensions of the (three-dimensional) space, in addition to the correct installation of data receiving machines, the very good quality of incoming signals is required. Implementing the control software of the GNSS stations used internationally, the scientific team of ISMOSAV performs data quality control for all GNSS stations of its permanent network. Also the data from all stations are beeing processed at regular time intervals using various   software that are installed on the server of the research team at AUTh (such as Bernese, LeicaGeOffice, BNC_PPP, TEQC etc.). After the initial quality check of the data, the stage of analysis and processing is followed, in order to accurately determine the location of the stations using the relevant static determination ensuring the high quality of the positioning of the GNSS stations of the ISMOSAV network.

In the first stage of data process, the PPP (Precise Point Positioning) technique is performed. The application PPP (Precise Point Positioning) is characterized by quite good accuracy, continuous coverage of measurements, fast availability and high functionality. The specific web application used can calculate the position of a receiver (user) anywhere on Earth using only its observations. The derived results are used as approximate coordinates for the next phase.
At the last processing step the final solution as well as the continuous monitoring (on daily basis) of the GNSS stations coordinates is performed using the Bernese GNSS software (v5.2) running on Linux Platfoms at AUTh. To date, the data to be processed are availiable only from GPS and GLONASS satellite systems. The data used are code and phase pseudo-ranges on both frequencies. Achieving the high precision solution requires both the use of precise ephemeris and satellite clock corrections, provided by IGS and used by these services.