took place and finally iron deposits formed on the existing sulfur in the anoxic/oxic zone. The same phenomenon can be seen in very small sulfur caves where the interior has no sulfur, the cave opening is small and sulfur deposition occurs only at the anoxic/oxic interface or on the outer oxic surface, sometimes along with iron deposits over sulfur. The other categories, nonsulfur and salt (the latter so far only seen in Hawai’i), represent a departure from the flowing hot spring analogy. Nonsulfur steam caves have not yet been fully categorized, although unusual thin filamentous organisms have been enriched from the H5 salt cave, and from sulfur caves such as SW 3 in Lassen. Nonsulfur caves farther below are considered for their solid surface chemistry by means of energy dispersive X-ray microanalysis (EDX). Sampling of steam cave or vent ceilings depends on the nature of the surface. With highly acidic solfatara areas, cave ceilings can be delicate and sometimes only careful hand sampling is essential. With deeper nonsulfur caves sometimes encountered in Hawai’i, this is less of a problem because the cave ceilings are formed of hard lava and only shallow samples are obtained. However, sampling through a small opening into a deep cave interior is not without its challenges, principally resulting from the high level of heat encountered, with or without leather gloves.
Table 1.1 Fumarole sampling locations and physical properties.
| Location | pH | Temp (°C) | Type | Chemistry |
| Hawai’i Volcanoes National Park1 | ||||
| Hawai’i (1) | 5.5 | 65.0 | Cave | Nonsulfur |
| Hawai’i (2) | 5.2 | 68.0 | Cave | Nonsulfur |
| Hawai’i (3) | 3.0 | 82.0 | Cave | Sulfur |
| Hawai’i (4) | 3.0 | 82.0 | Cave | Iron/sulfur |
| Hawai’i (5) | 5.0 | 68.0 | Cave | Salt |
| Hawai’i (6) | 4.5 | 66.0 | Cave | Salt/sulfur |
| Lassen Volcanic National Park2 | ||||
| Sulphur Works, lower (1) | 4.5 | 87.0 | Cave | Nonsulfur |
| Sulphur Works, lower (2) | 3.2 | 93.0 | Vent | Sulfur |
| Sulphur Works, lower (3) | 4.0 | 91.5 | Cave | Sulfur |
| Sulphur Works, upper (4) | 3.0 | 85.5 | Vent | Iron |
| Sulphur Works, upper (5) | 2.5 | 81.2 | Cave | Iron |
| Valles Caldera National Preserve3 | ||||
| Sulphur Springs, New Mexico | 2.0 | 89.0 | Cave | Nonsulfur |
| Pozzuoli, Italy4 | ||||
| Solfatara Crater | 3.0 | 94.0 | Vent | Sulfur |
1 June 2016 sampling
2 Oct 2018 sampling
1.3.1 Steam Collection
Samples of steam were collected from fumaroles in four permanently protected geothermal areas, Lassen Volcanic National Park, Hawai’i Volcanoes National Park, Valles Caldera National Preserve, and Solfatara Crater, Italy. Our steam collector (Figure 1.1) consists of a stainless shroud with a central holder for the sample tube. The condenser with a splash shield fits into the shroud and is slightly raised at 3 points, allowing excess steam to bypass the edges of the condenser during collection. The central lower guide rod directs condensed steam water into a sterile 50 mL polypropylene tube. During steam collection the open tube rests in a holder attached near the bottom of the shroud. The steam condenser can be handheld, but is also used attached to a tripod by an external mount, which by design serves to protect samples from aerial contaminants. During collection, rising steam contacts the water-cooled condenser and the guide rod drains the condensed steam water directly into the collection tube. After collection, the tube is immediately capped. Overall, the unit is portable, durable, corrosion resistant, easily autoclaved and produces contamination-free steam condensed samples and controls in a relatively short time period. In an average collection a 20–25 mL sample is collected in 15 min. Faster collections occur with