Equipment A DJI M600 Matrice Pro unoccupied aircraft system (UAS) was used for water and gas sampling, video, and thermal data collection. An Anafi Parrot UAS was also used on the 10/26/19 campaign for video and photography. Payload The sUAS carried a sampling payload connected to a remote release jaw mechanism. The water sampler was a 1-L Hydrasleeve, a flexible ultra high molecular weight (UHMW) plastic sleeve open at the top end, with a UHMW plastic inlet cone. The Hydrasleeve was attached 10 m below the UAS release jaw, with 3/16” polypropylene rope tied to the inlet cone. A swivel was tied to the top of the rope and connected to the release jaw. A 454 g (1 lb) stainless steel weight attached to the bottom provided needed ballast to counteract cross wind effects during flight. A nylon plastic tab was added to the bottom of the sleeve for reinforcement. Total payload weight was 0.8 kg empty, and 1.8 kg filled with 1-L water sample. Field operations The field operations site for the sampling and flight crew, and the adjacent sUAS take-off and landing zone, was on the western rim of Halema’uma’u crater at 1141 m elevation. USGS and DOI remote pilots flew the UAS into Halema’ma’u crater to sample the water lake deep within. The sampling sites were up to 600 m below the launch site elevation and 1300 m horizontally away. Flight operations extended beyond visual line of sight (BVLOS). Pilots used UAS visual and thermal camera streams to navigate. Flight crew observers used binoculars to support pilot navigation. Greater speed over ground was possible on the return flights, due to the extra ballast weight of the sample water preventing the suspended payload from blowing back and up toward the vehicle. The sample flights each lasted about 15 minutes. Sample collection The sampling payload was dipped into the lake to the sampling depth, between 0 to 5m below surface. The pilot judged depth via the camera stream, using colored flagging tape tied along the suspended sampling line at measured intervals. During descent through the water column, the flexible plastic sleeve was compressed and empty. After reaching depth, the water sample sleeve was retrieved upward and filled with water. A quick upward lift maneuver most effectively filled the sleeve, increasing water flow into the top inlet cone. A surface sample was collected by dragging the sleeve and cone across the water surface with a buoyant thermometer attached. The pilot visually confirmed a water sample had been collected. The sUAS returned to the landing zone. The return leg was an upward trip carrying the additional sample water weight. At the crater rim, the sUAS hovered adjacent to the landing zone, where the ground crew caught the suspended sample at standing height. The pilot used the remote release mechanism to drop the hanging line, then landed the UAS. The sample sleeve was stabilized for decanting by laying it out on a 3’ length of pvc pipe, halved lengthwise for the purpose. Sample handling Before each sample flight, the payload components were decontaminated with 70% isopropyl alcohol spray. New water sample sleeves were used for each sample. A plastic tarp was spread over the loose tephra of the sampling area to maintain cleanliness. At the field operations site, the sampling crew decanted the sleeve sample into 500 mL HDPE bottles through a puncture straw. Aliquots for isotope and alkalinity analyses were immediately filled in glass bottles. Sample water pH was measured in the field on partially cooled samples. An ExStik II multiparameter water quality instrument was used.