Low-cost, fast deployment multi-sensor observations of the 2021 Cumbre Vieja eruption&amp;#160;

&amp;lt;p&amp;gt;The management of natural hazards is a vital concern for the sustainable development of any country and information is the single most important factor to tackle the risks from natural hazards within the risk reduction phase, and to manage response during a crisis. To cope with these challenges it is required, on one hand, to collect baseline information on the natural systems to understand their current state, to identify changes and predict or forecast their future behaviour and, on the other hand, to update information during crisis to review and determine management strategies.&amp;lt;/p&amp;gt;&amp;lt;p&amp;gt;One major difficulty to this approach is the economic weight of the classic monitoring systems, requiring heavy investments, costly maintenance, and substantial human resources. To overcome these obstacles, an alternative concept was developed based on low-cost and fast deployable wireless sensors networks made by autonomous devices, each capable to communicate to a cloud computing service that compiles and processes data, producing information readily accessible via web.&amp;lt;/p&amp;gt;&amp;lt;p&amp;gt;The 2021 eruption of the Cumbre Vieja volcano presented an excellent opportunity for a proof of concept of this idea. A trial run was set up on this challenging environment, focusing mainly on the detection and measurement of eruptive products, targeting the measurement of eruptive plume components, such as carbon dioxide (CO&amp;lt;sub&amp;gt;2&amp;lt;/sub&amp;gt;), sulphur dioxide (SO&amp;lt;sub&amp;gt;2&amp;lt;/sub&amp;gt;) and ash (particle matter, PM), and the monitoring of lava flows entering the sea. Besides the sensor&amp;amp;#8217;s setups, also the automatic data processing and different communications were tested.&amp;lt;/p&amp;gt;&amp;lt;p&amp;gt;The experiment consisted of a proximal network of different stations measuring CO&amp;lt;sub&amp;gt;2&amp;lt;/sub&amp;gt;, SO&amp;lt;sub&amp;gt;2&amp;lt;/sub&amp;gt;, PM&amp;lt;sub&amp;gt;10&amp;lt;/sub&amp;gt;, PM&amp;lt;sub&amp;gt;2.5&amp;lt;/sub&amp;gt;, temperature, and humidity; a set of trials to intercept the eruptive plume with weather balloons to measure in-situ the same parameters; a distal aethalometer to detect particles from the distal plume; and a set of buoys to monitor hydroacoustic and environmental parameters in the proximity of the lava deltas. The proximal network allowed for a continuous monitoring with information immediately available via web, with good spatial and temporal correlations between different parameters. The atmospheric soundings allowed to measure particle mass concentrations and sulphur dioxide along a profile of the eruptive plume and characterize its vertical profile, with in situ measurements, while back trajectory of air parcel analyses and aethalometer measurements carried out at Iza&amp;amp;#241;a Atmospheric Observatory (2367 m.a.s.l.) showed attenuation variability that could be associated with small volcanic particles transported to at least 140 km from the source. The buoys trial allowed to record the acoustic environment near the lava deltas and to test the design and configurations of the device regarding sensors integration and communications.&amp;lt;/p&amp;gt;&amp;lt;p&amp;gt;The Cumbre Vieja eruption experiment allowed to try-out a fast deployment low-cost multi-sensor system with good results on volcanic plume characterization and real-time data production that proved to be useful for managing volcanic crisis and demonstrated the relevance of this alternative monitoring concept.&amp;lt;/p&amp;gt;