Reykjadalur Field Notes

Reykjadalur: Field Notes & Research Dossier

Series: Iceland Explained · Public Production Bible & Research Companion
Region / Municipality: South Iceland (Suðurland) · Sveitarfélagið Ölfus (trailhead at Dalafell/Hveragerði border, 3 km north of Hveragerði, Árnessýsla)
Primary Coordinates: 64.0219, -21.2106 (64°01'19"N, 21°12'38"W: Klambragil Bathing Reach)
Writer's Source-Check Date: November 1, 2026 (selected claims independently rechecked; scope noted below)

1.0 Site Dossier & The Reality Check

1.1 Etymology, Names & Toponymy

Every place name along the trail from the Hveragerði valley mouth into the upper basin of Reykjadalur encodes volcanic vapor, glacial gullies, carbonated springs, or subarctic birds:

• Reykjadalur (/ˈreiːcaˌtaːlʏr/) & Reykjadalsá (/ˈreiːcatalsˌauː/): Compound of Old Norse and Icelandic reykur (genitive plural reykja, "smoke" or "geothermal steam") and dalur ("valley"), plus á ("river"). Literally "Steam Valley" and "Steam Valley River." Downstream, after joining the drainage of Grændalur above Hveragerði, the Reykjadalsá becomes the Varmá ("Warm River") [S1, S3].
• Rjúpnabrekkur (/ˈrjuːpnaˌprɛhkʏr/): From rjúpa (genitive plural rjúpna, "rock ptarmigan", Lagopus muta) and brekkur ("slopes"). "Ptarmigan Slopes": the steep eastern switchback ascent climbing out of the Djúpagil basin onto the palagonite ridge [S3].
• Djúpagil (/ˈtjuːpaˌcɪːl/) & Djúpagilsfoss (/ˈtjuːpacɪlsˌfɔsː/): Compound of djúpur ("deep"), gil ("narrow ravine or gorge"), and foss ("waterfall"). "Deep Gorge" and "Deep Gorge Waterfall": the sheer Pleistocene hyaloclastite and columnar-basalt chasm flanking the western side of the ascent trail [S2, S4].
• Klambragil (/ˈkʰlampraˌcɪːl/): From klömbr (genitive plural klambra, "vice, smith's pinch, or narrow rock wedge/pass") and gil. "Pinch Gorge": the narrow glaciofluvial gully at the head of the inner valley where boiling alkaline and carbonic springs (kolsýruhverir) discharge into the cold mountain stream to create the warm bathing river [S3].
• Ölkelduháls (/ˈœlˌcɛltʏˌhauls/) & Ölkelduhnúkur: From ölkelda ("mineral or carbonic acid spring", literally "ale-spring") and háls ("ridge") / hnúkur ("peak"). The hydrothermal ridge immediately northeast of Reykjadalur connecting the Grensdalur system toward Hrómundartindur and Hengill [S3, S5].
• Grensdalur (/ˈkrɛnsˌtaːlʏr/): "Lair Valley": designates the extinct Pleistocene central volcano, described on the official panel as active roughly 120,000 years ago; its eroded terrain hosts the geothermal features of Reykjadalur and Grændalur [S3, S6].
• Jórukleif (/ˈjouːrʏˌkʰleiːf/): "Jóra's Cliff/Cleft": the steep fault pass on Mount Dyrafjöll north of the Hengill-Reykjadalur system named after the cannibal troll-woman Jóra (formerly Jórunn of Ölfus) in Jón Árnason's folk collection [S7, S8].
• Hverafuglar (/ˈkʰvɛːraˌfʏklar/): "Hot-Spring Birds": legendary small dark birds said in local folklore to swim inside boiling cauldrons around Reykjadalur and Ölkelduháls [S3].

1.2 Key Waypoints & Spatial Layout

Waypoint / Sub-Location	Approximate Coordinates (Decimal; not surveyed navigation points)	Elevation / Scale	Functional Role in the Reykjadalur System
Dalafell Trailhead (Car Park)	64.0092, -21.1917	~80 m a.s.l. · 3.0–3.5 km one-way hike to bathing zone	Lower trailhead north of Hveragerði where the Reykjadalsá and Grændalsá merge into the Varmá; marked by roaring district borehole steam [S1, S3].
Rjúpnabrekkur Switchbacks	64.0145, -21.1985	~110–210 m a.s.l. · Steep palagonite tuff ascent	Primary climbing grade exposing yellow-brown subglacial móberg scree; turns into a blue glare-ice chute in winter [S3].
Djúpagil Gorge & Djúpagilsfoss	64.0172, -21.2035	~195 m a.s.l. · ~20 m vertical cascade	Deep canyon West of Rjúpnabrekkur slicing through stacked Holocene basalt columns and Pleistocene palagonite breccia [S2, S4].
Large Mud Cauldron & Footbridge	64.0201, -21.2088	~230 m a.s.l. · Fenced acid-sulfate mud crater	Violently churning grey altered-clay mud pot surrounded by iron-stained banks and sulfur crusts [S3].
Klambragil Bathing Reach (Pine Boardwalks)	64.0219, -21.2106	~245 m a.s.l. · 36–40°C stone-weir mixing pools	Hydrothermal collision zone where 90–100°C alkaline and carbonic springs from Klambragil mix with cold highland snowmelt [S3, S9].
Ölkelduháls & Ölkelduhnúkur Ridge	64.0385, -21.2150	~360–442 m a.s.l. · ~2 km N of Klambragil	High-temperature solfatara ridge with rhyolite outcrops, carbonic springs, and folklore of the boiling hverafuglar [S3, S5].
Reykir í Ölfusi (Ingólfur Arnarson’s Last Farm)	64.0068, -21.1768	~65 m a.s.l. · Foot of Reykjafjall / Reykjadalur	Historic settlement farm where Landnámabók records that Iceland’s first settler, Ingólfur Arnarson, spent his final years old and blind [S3].

1.3 The Postcard Myth vs. Ground Reality

On Golden Circle and South Coast itineraries, Reykjadalur ("Steam Valley") is promoted as a gentle wilderness spa: an easy walk into a green mountain pasture where visitors lounge in a naturally warm lazy river and smear therapeutic mineral mud on their cheeks [S1, S9].

On the ground, the hiker is stepping onto the thin, acid-leached lid of an active hydrothermal reactor:

• A Turbulent Thermal Collision, Not a Uniform Spa Pool: The bathing stretch of the Reykjadalsá at Klambragil is an unbuffered hydraulic truce between near-freezing snowmelt draining off the Hellisheiði/Hengill moorlands and 90–100°C geothermal water pouring out of the Klambragil gully [S3, S9]. Low rock weirs stacked across the bed blend the two inflows toward 36–40°C, yet incomplete mixing persists: a bather lying on the cobbles can feel an icy ribbon of mountain runoff numbing one hand while a vein of scalding spring water stings the other [S3, S9].
• Wet Rust & Acid Porridge (The February 2017 Crust Collapse): The vivid crimson, yellow, and bone-white banks reflect geothermal alteration; iron oxides can produce the red staining that invites the "wet rust" comparison. Exact mineral proportions and skincare benefits are not established by [S3, S6]. Beneath a paper-thin surface crust of moss and clay sits 90–100°C slurry. In February 2017 (archival source; link unavailable), 24-year-old Canadian visitor Nicole Rakowski stepped onto apparently firm ground beside the river after changing into her swimsuit; the crust snapped, plunging her leg knee-deep into a boiling vent and requiring fellow visitors to carry her downhill toward rescuers in an area where the group could not obtain mobile reception [S11].

2.0 Earth & Water Architecture (Geology, Hydrodynamics & Chemistry)

2.1 Tectonic Setting & Deep-Time Formation

Reykjadalur is a deep glacial and glaciofluvial valley incised into the eastern structural margin of the Hengill triple junction, where the Reykjanes Peninsula oblique rift, the Western Volcanic Zone (WVZ), and the transform faults of the South Iceland Seismic Zone (SISZ) pull the North American and Eurasian plates apart at roughly 2 centimeters per year [S3, S6, S10].

While the active central volcano of Hengill rises to 803 meters at Skeggi to the west (having last erupted Holocene lava ~1,900–2,000 years ago and rifted during the 1789 tectonic crisis), Reykjadalur and Grændalur occupy terrain associated with the extinct Pleistocene central volcano of Grensdalur [S3, S6]. The official panel describes Grensdalur as active roughly 120,000 years ago, subsequently displaced eastward relative to the active zone and deeply eroded by glaciers [S3]. Regional borehole work describes heat supply through fractures connected to the active Hengill rift; it does not establish >200°C at exactly 1,000 metres beneath the bathing reach [S6].

Stratigraphically, the valley walls expose three distinct volcanic lithologies:

• Subglacial Palagonite Tuff (Móberg) & Hyaloclastite Breccia: The steep switchbacks of Rjúpnabrekkur and the crags of Ölkelduhnúkur consist of yellowish-brown palagonitized sideromelane tuff formed when Pleistocene basaltic magma erupted into meltwater vaults beneath a thick glacial ice sheet, flash-quenching into brittle volcanic glass [S3, S5].
• Holocene & Interglacial Tholeiitic Basalt: Dark grey, columnar-jointed basalt lava sheets cap the ridges and form the vertical rock step of Djúpagilsfoss [S2, S4].
• Evolved Silicic Rhyolite (>69% SiO2): Along the upper walls of Klambragil and Ölkelduháls, pale pinkish-yellow and cream-colored rhyolite intrusions and lavas, characteristic of mature central volcanoes like Grensdalur, crop out above the hydrothermal vents [S3, S5].

2.2 Hydrodynamics, Thermal Systems & Optical Physics

The hydrothermal circuit of Reykjadalur is fed by meteoric water (rain and snowmelt) circulating through fractured volcanic rock; the regional model connects heat supply to the active rift zone through faults and fissures [S6].

At the head of the inner valley, the glaciofluvial gorge of Klambragil intersects multiple fault conduits, discharging two distinct fluid types into the cold highland stream of the Reykjadalsá [S3]:

• Alkaline Chloride-Silica Hot Springs (90–100°C): Hot water supplies much of the river's heat [S3]. Cooling geothermal water can precipitate amorphous silica (SiO2), which is chemically distinct from volcanic glass. The cited local sources do not establish particle sizes, a measured optical mechanism, or silica as the cause of the bathing pools' colour.
• Carbonic Soda Springs (Kolsýruhverir): Rare carbonate-rich vents discharging dissolved carbon dioxide (CO2) and bicarbonates along Klambragil and neighboring Ölkelduháls ("Ale-Spring Ridge") [S3].

On May 29, 2008, at 15:45 UTC, the magnitude 6.3 (Mw) Ölfus earthquake involved north-south strike-slip faulting in the wider region [S10]. The cited ground-motion study does not document the claimed Reykjadalur canyon landslides, silica-caprock failure, or specific changes to the river's spring supply; those local mechanisms require separate evidence.

2.3 Geochemistry & Surface Alteration

The saturated colors of Reykjadalur's hillsides are the product of aggressive acid-sulfate alteration [S3, S6]. When ascending steam carries hydrogen sulfide (H2S) into the shallow vadose zone, reaction with atmospheric oxygen and groundwater oxidizes H2S into sulfuric acid (H2SO4) and native elemental sulfur (S, which precipitates as bright yellow crystalline crusts around fumarole rims) [S3, S6].

Sulfuric acid attacks the surrounding basalt and rhyolite, leaching away mobile cations and transforming hard volcanic rock into a boiling, thixotropic paste of kaolinite and smectite clay (seen in the grey mud cauldron the large mud pot beside the footbridge) [S3]. Simultaneously, ferrous iron (Fe2+) leached from basaltic pyroxene and olivine oxidizes upon exposure to air into insoluble ferric iron (Fe3+), painting the riverbanks and clay slopes in vivid bands of blood-red hematite (Fe2O3) and ochre-yellow limonite/goethite (FeO(OH)) [S3, S6].

3.0 Living Ecosystem & Seasonal Biology

3.1 Botanical Succession & Micro-Habitats

Reykjadalur's biological communities are sorted along steep thermal gradients, ranging from 95°C vents down to subarctic heath:

• Geothermal Microbes & the Astrobiology Connection: The official panel records diverse bacteria and archaea in the valley [S3]. Icelandic geothermal studies provide background on communities shaped by temperature and chemistry, and hydrothermal systems interest astrobiologists [S12]. They do not establish Gallionella at Reykjadalur or identify its coloured mats by sight. The species assignments and exact 60–75°C / 45–60°C / <45°C colour bands are therefore unverified; colour is not a safe thermometer.
• Red-Listed Geothermal Vascular Flora: Warm ground radiation keeps the soil snow-free through winter, sheltering two nationally protected Red-List plant species documented by the Icelandic Institute of Natural History:
  • Small Adder's-tongue (Ophioglossum azoricum, Icelandic: naðurtunga): A tiny, primitive spore-bearing fern restricted in Iceland almost exclusively to warm geothermal turf [S3].
  • Blue Water-speedwell (Veronica anagallis-aquatica, Icelandic: laugadepla): An aquatic herb rooting directly in the warm, mineral-rich shallows of the Reykjadalsá alongside marsh willowherb (Epilobium palustre) [S3].

3.2 Fauna, Aquatic Life & Migration Windows

• Rock Ptarmigan (Lagopus muta / Rjúpa): Resident year-round on the heather and palagonite slopes of Rjúpnabrekkur ("Ptarmigan Slopes"), molting from speckled grey-brown summer plumage into pure white winter feathers [S3].
• Common Snipe (Gallinago gallinago / Hrossagaukur) & Golden Plover (Pluvialis apricaria / Lóa): Arrival from April to September brings nesting waders to the warm sedge marshes of the upper valley, where male snipes perform steep twilight courtship dives that vibrate their outer tail feathers in a resonant "drumming" bleat [S3].

4.0 Human Stratigraphy: History, Sagas, Folklore & Material Culture

4.1 Settlement, Chronicles & Political/Religious History

• Ingólfur Arnarson at Reykir í Ölfusi (Landnámabók): According to the Landnámabók (Book of Settlements) tradition preserved on official municipal heritage plaques in the valley, Iceland's first permanent Norse settler, Ingólfur Arnarson, whose namesake table mountain, Ingólfsfjall, rises immediately east across the valley mouth, spent his final years old and blind at the farmstead of Reykir í Ölfusi at the foot of the Reykjadalur hills [S3].
• A Thousand Years of High-Risk Winter Sheep Grazing: Prior to twentieth-century recreational hiking, Reykjadalur was working pastoral infrastructure for the farms of Ölfus. Because geothermal soil heat kept grass growing in late autumn and early spring when surrounding highlands were locked under snow and ice, shepherds drove ewes into the valley for winter grazing [S3]. Warm ground beside boiling vents presents a livestock hazard, but [S3] records the grazing tradition without documenting frequent fatal collapses.

4.2 Micro-History, Architecture & Domestic Survival

• Boardwalks, X-Screens & Rescue Stakes: Heavy visitor traffic damages fragile banks and vegetation. Wooden access structures, open changing screens, barriers, and numbered trail stakes help channel movement and locate emergencies [S3]. Landvernd coordinated the nature and safety panels with local partners; its June 2014 account separately records trail improvements in 2012–2013 by Ölfus, Hveragerði, the Agricultural University at Reykir, and Eldhestar. It does not identify Landvernd as builder of every boardwalk or establish the screens' structural design intent [S3a].
• The February 2017 Crust Collapse (Nicole Rakowski Rescue): On a winter afternoon in February 2017 (archival source; link unavailable), 24-year-old Canadian visitor Nicole Rakowski changed into her swimsuit beside the bathing river and stepped onto ground she believed was firm beside the river [S11]. The brittle mineral crust snapped, plunging her leg knee-deep into a hidden boiling vent [S11]. Pulled out by her friends, she described peeling skin and loss of consciousness from pain; the group could not obtain mobile reception in the valley [S11]. Four men, including Californian paramedic Lee Ricasa, carried her downhill toward rescuers while her friend ran ahead seeking phone reception. On the descent, the group encountered an Icelander training for rescue work who used his radio to call for further help [S11].

4.3 Folklore, Ghosts & Hazard Encoding

Local folklore around the Hengill–Reykjadalur passes encodes both mountain-fog disorientation and the inverted physics of boiling vents:

1. The Cannibal Giantess Jóra of Jórukleif: Collected in Jón Árnason's Íslenzkar þjóðsögur og ævintýri, the legend begins with a farmer's daughter in Sandvíkurhreppur in Flói [S7, S8]. When Jórunn saw her father's horse losing a horse fight, she tore a thigh from the rival horse and fled with it. She threw a boulder into the Ölfusá to cross the river, reached Hengill, and became the monstrous troll-woman Jóra, who laired in the pass of Jórukleif on Mount Dyrafjöll and ambushed travelers and horses in the mountain fog, until a young man armed with a silver-inlaid axe and instructions from the King of Norway killed her at sunrise on Whitsun morning, sending her axe drifting into the river Öxará at Þingvellir [S7, S8].
2. The Hverafuglar ("Hot-Spring Birds") of Reykjadalur and Ölkelduháls: Preserved in local oral tradition and on the Landvernd / Ölfus heritage panels, the hverafuglar were described as small, dark-plumaged birds that swam calmly inside violently boiling cauldrons around Reykjadalur, Hagavíkurlaugar, and Ölkelduháls [S3]. According to the legend, if a hunter caught a hverafugl and tried to cook it in a pot of boiling water, the meat remained completely raw; the bird could only be cooked by plunging it into ice-cold water [S3].

4.4 Cultural & Pop-Culture Footprint (Verified vs. Myth)

• Game of Thrones Season 4 Finale (Brienne vs. The Hound): Confirmed for the wider Hengill/Nesjavellir volcanic pass system. HBO filmed the brutal cliffside sword-and-boulder fight between Brienne of Tarth (Gwendoline Christie) and Sandor "The Hound" Clegane (Rory McCann) across the steaming palagonite and basalt ridges of the Hengill geothermal area.
• The "Geothermal Collagen Mud Mask" Tourist Claim: Unsubstantiated. Visitors routinely scoop red clay from the banks of the Reykjadalsá and smear it on their faces, assuming it is skin-rejuvenating spa mud like the white silica of the Blue Lagoon. Iron oxides can stain geothermal clay red, but neither its exact mineral assemblage, particular iron-oxidizing microbes, nor skincare efficacy is established for these banks by [S3, S6, S12]. Fragile ground beside hot vents should be left undisturbed.

5.0 Scout & Local Insider Readout (Light, Sound, Seasons & Vicinity)

5.1 Tactile & Acoustic Profile

• Rain-Modulated Mud-Pot Bass: In the upper thermal basin around the large mud pot, the acoustic pitch of the mud pots tracks recent weather: after dry summer weeks, the thickened grey kaolinite paste traps gas until it bursts with a slow, low-frequency bass thud felt in the chest; after heavy rain, diluted slurry boils with a rapid, high-pitched splatter [S3].
• Thermal Seams in Klambragil: Inside the stone-dammed bathing pools (245 m a.s.l.), cold highland water mixes incompletely with hot spring inflows from Klambragil. Temperature can change sharply over short distances; the cited sources do not establish a fixed 10–15°C change or a stable vertical layering [S3, S9].

5.2 Seasonal Morph & Optical Windows

• Summer White-Out Steam Diffusion: When a crosswind pushes fumarole plumes across the trail under high midday sun, Mie scattering inside the water droplets flattens the valley into a blinding white veil for seconds before parting to reveal high-contrast oxblood hematite (Fe2O3), yellow sulfur (S), and neon-green moss [S3, S5].
• Winter Glare-Ice Switchbacks (November–April): Compacted snow and condensing steam freeze the steep switchbacks of Rjúpnabrekkur into solid blue glare ice (svell), while up at the river (36–40°C), wet hair and swimsuits can freeze stiff after stepping out behind the unroofed wooden X-screens into sub-zero wind.

5.3 The Vicinity Scan (Connected Nearby Sites)

1. Grændalur ("Green Valley", 1.5 km E): The uncrowded sister valley directly over the Grensdalur volcano core, connected via an upland loop trail over the ridge from Reykjadalur [S3, S6].
2. Ölkelduháls & Ölkelduhnúkur (2–3 km N): High-altitude rhyolite and solfatara ridge continuing the hike north toward Bitra and Hengill [S3, S5].
3. Hveragerði & Hveragarðurinn (EP_12, 3 km S): The geothermal greenhouse town at the mouth of the valley where the Reykjadalsá becomes the Varmá [S1].

6.0 Field Realities, Hazards & Verified Bibliography

6.1 Physical Hazards & The Stupid Tax

• Hidden Vent Crust Collapse (90–100°C Third-Degree Burns): Outside the pine boardwalks, hydrothermally leached clay and moss form a thin, dry-looking crust over boiling mud and water vents. Stepping off the boardwalk, even to set down a backpack or take a photograph, can snap the crust and cause catastrophic lower-limb scalds in an area with patchy or zero mobile phone reception [S3, S11].
• Icy Descent on Rjúpnabrekkur & Post-Soak Hypothermia: Descending the steep palagonite switchbacks of Rjúpnabrekkur in winter without steel microspikes (broddar) raises the risk of falls and serious injury; in winter gales, lingering wet in the wind after exiting the 40°C river triggers rapid core-temperature drop.

6.2 Practical Field & Equipment Notes

• Mandatory Gear: Wear ankle-supporting waterproof hiking boots and pack steel microspikes (broddar) from October through April; bring a quick-dry towel, a windproof hardshell jacket, a warm beanie, and a dry bag to keep clothes dry against blowing rain/snow on the unroofed X-screen hooks.
• Emergency Location: Call 112 and give the number on the nearest trail stake if known [S3]. Reception may be unavailable [S11]; no fixed climb of 100 metres guarantees a signal, and searching for reception must not lead onto unmarked geothermal ground. Check current closures on SafeTravel before setting out [S1].

6.3 Open Research Notes & Source Discrepancies

• Grensdalur Chronology & Reservoir Temperatures: The official panel describes volcanic activity roughly 120,000 years ago [S3]. Suryanto (2021) discusses a regional shift of the active system over 500,000–1 million years and reports a maximum temperature of about 190°C in the studied Hveragerði well data. It does not establish a 300,000–700,000-year construction phase reconciled by late activity at 120,000 BP, or >200°C at 1,000 metres beneath the Reykjadalur bathing reach [S6].

6.4 Verified Sources & Archives

• [S1] Visit South Iceland: Reykjadalur Valley & Golden Circle Day Tours: Reykjadalur Guide · Verified passages: Trailhead access north of Hveragerði, 3 km ascent, and bathing river overview.
• [S2] Guide to Iceland (Regína Hrönn Ragnarsdóttir): Reykjadalur Hot Spring Valley in South Iceland · Verified passages: Trail geography, Djúpagil canyon, Djúpagilsfoss waterfall, and upper valley mud pots.
• [S3] Landvernd & Sveitarfélagið Ölfus: Reykjadalur Official Trail & Geological Information Panel · Primary Icelandic scientific and historical field dossier. Verified passages: Extinct Grensdalur central volcano (described as active roughly 120,000 years ago), Rjúpnabrekkur, Klambragil alkaline and carbonic springs (kolsýruhverir), the large mud pot, Red-Listed flora (Ophioglossum azoricum / naðurtunga and Veronica anagallis-aquatica / laugadepla), ptarmigan and snipe fauna, Landnámabók record of blind Ingólfur Arnarson at Reykir í Ölfusi, pastoral use of warm ground, and the hverafuglar ("hot-spring birds") legend.
• [S3a] Landvernd, June 25, 2014: Upplýsingaskilti um náttúru og öryggismál í Reykjadal. Distinguishes the information-panel partnership from 2012–2013 trail improvements. https://landvernd.is/upplysingaskilti-um-natturu-og-oryggismal-i-reykjadal/
• [S4] Komoot: Djúpagilsfoss Highlight · Verified passage: Position and basalt/palagonite cliff drop of Djúpagilsfoss along the Rjúpnabrekkur ascent.
• [S5] Guide to Iceland (Regína Hrönn Ragnarsdóttir): The Colourful Geothermal Areas by Mt. Ölkelduhnúkur and Ölkelduháls · Verified passage: Rhyolite and acid-sulfate alteration across Ölkelduháls and Ölkelduhnúkur immediately north of Reykjadalur.
• [S6] Sigit Suryanto (2021), GRO Geothermal Training Programme: Geological Modelling of the Hveragerdi Geothermal Field, Iceland, Report 26. Scope: regional geology, fracture-connected geothermal circulation, and Hveragerði borehole alteration/temperature data; not a temperature profile beneath the Reykjadalur bathing pools. https://www.grocentre.is/static/files/GTP/Publications/SixMonth2021/26-sigit.pdf
• [S7] Guide to Iceland (Regína Hrönn Ragnarsdóttir): The Certifiable Giantess Jóra in Jórukleif · Verified passage: Jón Árnason's legend of Jórunn of Sandvíkurhreppur in Flói becoming the cannibal giantess Jóra of Jórukleif on Mount Dyrafjöll and her slaying at dawn on Whitsun.
• [S8] Guide to Iceland: Nesjavellir & Jórukleif Hike · Verified passage: Topographic link between the Hengill/Reykjadalur trail network, Jórukleif, and Þingvallavatn.
• [S9] Hot Springs Iceland: Reykjadalur Hot Spring River · Verified passage: 36–40°C bathing pools, stone weirs, and Klambragil mixing mechanics.
• [S10] Halldórsson, B. & Sigbjörnsson, R. (2009): Extreme near-fault strong-motion of the M6.3 Ölfus earthquake of 29 May 2008 · Scope: strong motion and faulting during the May 29, 2008 Mw 6.3 Ölfus earthquake; not evidence of specific Reykjadalur spring or caprock changes.
• [S11] Benedikt Bóas, Vísir, April 5, 2017: Hélt að hún myndi deyja í Reykjadal (interview with Nicole Rakowski). Supports her February 2017 scalding, friends pulling her out, four men including Lee Ricasa carrying her downhill, lack of phone reception, and a radio-equipped rescue trainee encountered on the descent. Does not establish a single step off a boardwalk or a continuous three-kilometre hand-carry. https://www.visir.is/g/2017632285d/helt-ad-hun-myndi-deyja-i-reykjadal
• [S12] Tobler, D. J. & Benning, L. G. (2011), Bacterial diversity in five Icelandic geothermal waters: temperature and sinter growth rate effects, Extremophiles 15, 473–485, doi:10.1007/s00792-011-0378-z; Matís bacteria/archaea topic index. Regional background only: these citations do not establish Gallionella or exact species/temperature colour bands at Reykjadalur. https://doi.org/10.1007/s00792-011-0378-z

Questions and answers

How does the Reykjadalur hot spring river get its warm temperature? Located 3 kilometers uphill from Hveragerði inside the eroded roots of the extinct Grensdalur central volcano, the bathing river (Reykjadalsá) is formed where 90–100°C alkaline and carbonic hot springs from the Klambragil gorge pour into a cold highland meltwater stream, blending behind low stone weirs to 36–40°C.

Is the red mud on the banks of Reykjadalur good for your skin? It is not a tested skincare product. Iron oxides can stain geothermal clay red, but colour alone does not establish its exact minerals or microbes. Do not disturb fragile banks beside scalding vents.

Why is stepping off the wooden boardwalk in Reykjadalur dangerous? Hydrothermal acid leaches the rock underneath the valley floor while leaving a thin, firm-looking crust of mud and moss on top; stepping off the pine boardwalk can snap this crust over a 90–100°C vent, as happened in February 2017 when a hiker suffered severe third-degree burns and was carried downhill by fellow visitors toward rescuers; a radio-equipped trainee encountered on the descent called for further help.