THE STORY
Contents
- Fagradalsfjall, Meradalir & Litli-Hrútur: The Buried Sheep Valley, the 1943 Bomber in the Fog, and the Lava That Still Clicks
- Quick Facts: The Fagradalsfjall Eruption Trilogy (2021–2023)
- Ísólfur's Wethers and the Liberator in the Fog: The Mountain Before the Webcams
- What the Olivine Crystals Remember: Earthen Dams, Burning Moss, and the Deep Mantle Window
- The Thermal Battery Under the Glass: Acoustic Contraction, Gas Bowls, and Trail Realities
- Frequently Asked Questions: Fagradalsfjall, Meradalir & Litli-Hrútur
- Is Fagradalsfjall still erupting, and how is it different from the Grindavík eruptions?
- Why does the cooled lava at Fagradalsfjall make a clicking or breaking-glass sound?
- Which hiking trails and parking lots serve Fagradalsfjall, and how do I check current access?
Fagradalsfjall, Meradalir & Litli-Hrútur: The Buried Sheep Valley, the 1943 Bomber in the Fog, and the Lava That Still Clicks
Companion essay to the video episode: Fagradalsfjall Aftermath (The Eruption Trilogy: 2021–2023)
Before the evening of March 19, 2021, the deep mountain hollow of Geldingadalir (63.8890, -22.2700) on the eastern flank of Fagradalsfjall was one of the quietest grass basins in Southwest Iceland. Down on the valley flat, sheltered between the hill of Stórhóll and the pass of Nátthagaskarð, stood a low turf mound (þúst á flöt) that local oral tradition, preserved by Ferlir.is and Visit Reykjanes, though never excavated by archaeologists, identified as the grave of medieval farmer Ísólfur of Skáli (Ísólfur á Skála), who asked to be buried high in the hills where his castrated rams had their finest grazing. Above that green hollow, the fog-wrapped palagonite slopes of Fagradalsfjall held a darker twentieth-century memory: the shattered wreckage of the US Eighth Air Force B-24 Liberator Hot Stuff, which slammed into the mountain in driving rain on May 3, 1943, killing European Theater commander Lieutenant General Frank Maxwell Andrews and thirteen others.
Today, Ísólfur's sheep meadow lies sealed beneath a hundred and fifty million cubic meters of solid basalt. Between March 2021 and August 2023, three successive fissure eruptions, at Geldingadalir (2021), Meradalir (63.8980, -22.2450, in 2022), and Litli-Hrútur (63.9180, -22.2150, in 2023), ended an eight-hundred-year volcanic pause on the Reykjanes Peninsula and turned a lonely sheep valley into the most-watched geological amphitheater on Earth.
In the spoken episode, we walk through the sensory aftermath of that trilogy, beginning with the breaking-glass tinkle of winter lava contraction. Here on the page, we dig into the human and forensic layers beneath the spectacle: the pastoral folklore and wartime tragedy that defined Fagradalsfjall before the webcams arrived, the engineering battles against overflowing lava and burning moss, the olivine crystal chemistry that separates Fagradalsfjall's deep mantle plumbing from the shallow magma sill threatening Grindavík, and the real gas and trail hazards of a thirty-meter-thick thermal battery that is still cooling today.
Quick Facts: The Fagradalsfjall Eruption Trilogy (2021–2023)
| Attribute | Verified Field Data |
|---|---|
| Mountain & Valley Names | Fagradalsfjall (/ˈfaɣraˌtalsˌfjatl̥/, "Fair-Valley Mountain", ~385 m a.s.l. Pleistocene móbergsstapi) | Geldingadalir ("Valleys of the Wethers/Castrated Rams") | Meradalir ("Mares' Valleys") | Litli-Hrútur ("Little Ram") (Visit Reykjanes). |
| Eruption 1: Geldingadalir (2021) | March 19 – September 18, 2021 (181 days) | 8+ vents | Max discharge ~13 m³/s | Volume ~150 million m³ | Area ~4.8 km²; overflowed into Nátthagi in May–June 2021, overrunning earthen barriers; iron-rich surface now oxidized rust-red (Fe2O3) (Smithsonian GVP). |
| Eruption 2: Meradalir (2022) | August 3 – August 21, 2022 (18 days) | 300 m linear fissure | Max discharge ~32 m³/s | Volume ~12 million m³ | Area ~1.2 km²; ponded in the northern basin, burying 2021 hiking paths (Goldschmidt 2025). |
| Eruption 3: Litli-Hrútur (2023) | July 10 – August 5, 2023 (26 days) | 900 m en-echelon fissure | Initial discharge ~50 m³/s | Volume ~18 million m³ | Area ~1.5 km²; ignited ~250 hectares of dry Racomitrium moss heathland ("The Black Ring") (NASA Earth Observatory). |
| Magmatic Plumbing Divide | Fed by deep mantle/near-Moho reservoirs (9–20 km depth; primitive high-MgO melts in 2021 evolving in Moho sills by 2022–2023), distinct from the shallow 4–5 km crustal magma sill beneath Svartsengi feeding the 2023–2025 Sundhnúkur eruptions (ResearchGate Olivine Study). |
| Pre-2021 Human History | Traditional (unexcavated) burial mound of medieval farmer Ísólfur á Skála on the grassy floor of Geldingadalir; May 3, 1943 crash of US B-24 Liberator Hot Stuff on Fagradalsfjall, killing Lt. Gen. Frank M. Andrews and 13 others (1 survivor) (Visit Reykjanes; Wikipedia: Hot Stuff). |
| Trailheads & Current Access | Both official parking lots P1 (Geldingadalir) and P2 (Stóri-Leirdalur, 63.8587, -22.2786) sit off coastal Route 427 (Suðurstrandarvegur): Path A (~6–8 km one way / ~12–16 km RT, 2–2.5 hrs each way), Path C (Langihryggur, ~4 km one way), and Path E (to Litli-Hrútur, 18–20 km RT, 5–6 hrs). Because seismic unrest, gas, or weather can close roads and trails at short notice, always check live status on SafeTravel.is and Umferðin (Visit Reykjanes: Hiking and Parking). |
Ísólfur's Wethers and the Liberator in the Fog: The Mountain Before the Webcams
Before March 2021, if you asked ten people in Reykjavík to point out Geldingadalir on a map, nine of them would have stared at you blankly. For eight centuries after the medieval Reykjanes Fires died out in 1240, the elongated, flat-topped subglacial table mountain of Fagradalsfjall, the highest rise on the Reykjanes Peninsula at 385 meters above sea level, formed beneath Pleistocene glacial ice during the last hundred-thousand-year glacial cycle, was simply the rain-swept back pasture between Grindavík and the northern coast.
Yet the sheep farmers of Suðurnes knew every grass hollow tucked into its eastern flank, and they named each valley for the animals that grazed it: Meradalir ("Mares' Valleys"), Litli-Hrútur ("Little Ram"), Nátthagi ("Night Pasture"), and Geldingadalir ("Valleys of the Wethers," or castrated rams). Out in the middle of the flat green meadow at the bottom of Geldingadalir stood a low, weathered turf mound (þúst á flöt). According to local oral tradition recorded by Ferlir.is and Visit Reykjanes, a folk tradition preserved in place-name lore rather than confirmed by archaeological excavation, that mound was the burial place of Ísólfur of Skáli (Ísólfur á Skála), the early farmer who gave his name to the coastal homestead of Ísólfsskáli east of Grindavík. Before he died, Ísólfur asked his household not to bury him down by the salt surf, but to carry him up into the sheltered mountain bowl of Geldingadalir, "where his wethers had it best" ("þar sem geldingarnir hans hefðu það best"). For centuries, sheep cropped the grass over that mound in unbroken quiet, until March 19, 2021, when a fissure tore open across the valley floor and buried the pasture under dozens of meters of molten mantle rock.
Seventy-eight years before the lava filled Geldingadalir, the cloud-wrapped upper slopes of Fagradalsfjall claimed one of the most consequential aviation disasters of the Second World War. On the afternoon of May 3, 1943, a United States Army Air Forces B-24D Liberator heavy bomber named Hot Stuff (serial number 41-23728) was descending through driving rain and thick coastal fog toward a refueling stop at Keflavík Airfield on its flight from England to Washington, D.C. Three months earlier, on February 7, 1943, Hot Stuff had become the very first heavy bomber in the Eighth Air Force to complete twenty-five combat missions over occupied Europe, beating the famous Memphis Belle to the milestone by more than three months (US War Memorials).
Sitting in the passenger compartment that afternoon was Lieutenant General Frank Maxwell Andrews, Commander of all United States Forces in the European Theater of Operations (after whom Joint Base Andrews in Maryland was later named) and the officer widely expected to lead the Allied invasion of Europe (Wikipedia: Frank Maxwell Andrews). Coming in low under the cloud ceiling from the east, the four-engine bomber struck the steep palagonite flank of Fagradalsfjall. Fourteen of the fifteen men aboard, including General Andrews, died on impact. Only one man, tail gunner Staff Sergeant George A. Eisel, survived inside the severed tail section, lying trapped in freezing sleet for more than twenty-four hours (á annan sólarhring) before search parties reached the mountain slope (Visit Reykjanes).
What the Olivine Crystals Remember: Earthen Dams, Burning Moss, and the Deep Mantle Window
When magma finally broke through the floor of Geldingadalir on March 19, 2021, its first weeks looked deceptively tame: a steady fountain discharging up to thirteen cubic meters per second inside a natural stone bowl. By May and June 2021, however, the filling basin spilled south into the night-pasture valley of Nátthagi (63.8750, -22.2650). Icelandic engineers bulldozed tall earthen diversion dams across Nátthagi in a dress rehearsal for civil defense, hoping to keep the lava from severing coastal Route 427 (Suðurstrandarvegur) and buried fiber-optic cables; in June 2021, the slow-moving basalt pond overtopped the earthen berms before halting just short of the highway (Smithsonian GVP).
When the system ruptured a second time at Meradalir (August 3–21, 2022 along a 300-meter fissure at ~32 m³/s) and a third time farther north at Litli-Hrútur (July 10 – August 5, 2023 along a 900-meter fissure at ~50 m³/s), the hazard shifted from overflowing valleys to burning tundra. Because Litli-Hrútur opened during a bone-dry July drought, radiative heat and incandescent spatter from the fissure ignited the surrounding Racomitrium lanuginosum moss heathlands, burning roughly 250 hectares in the largest moss wildfires in recorded Icelandic history and leaving a wide "Black Ring" of carbonized peat around the glassy black 2023 pāhoehoe lava (NASA Earth Observatory; MDPI). Meanwhile, back at the older 2021 Geldingadalir vents, rainwater, oxygen, and escaping steam have oxidized the ferrous iron (FeO* ~10–12 wt%) in the basalt into crusts of brick-red hematite (Fe2O3) and mustard-ochre limonite around steaming fumarole halos.
Why did those three Fagradalsfjall eruptions behave like contained mountain laboratories, whereas the eruptions that began in late 2023 along the Sundhnúksgígar crater row just five kilometers west repeatedly tore open multi-kilometer curtains of fire threatening Grindavík and the Blue Lagoon?
The answer is locked inside microscopic green grains of olivine (ResearchGate Olivine Study; Goldschmidt 2025). Trace-element forensics show that the 2021 Geldingadalir eruption tapped primitive, magnesium-rich basalt (MgO ~8.5–10 wt%) rising almost directly from the crust–mantle boundary (Moho) at fifteen to twenty kilometers depth, while the 2022 Meradalir and 2023 Litli-Hrútur melts stalled and evolved chemically in interconnected mid-crustal and near-Moho sills at nine to twelve kilometers depth. By contrast, the Sundhnúksgígar system is fed by a shallow crustal magma accumulation zone just four to five kilometers beneath Svartsengi: a shallow hydraulic capacitor that inflates the ground until it ruptures violently at high discharge rates.
The Thermal Battery Under the Glass: Acoustic Contraction, Gas Bowls, and Trail Realities
Because the 2021 Geldingadalir vents erupted inside an enclosed mountain amphitheater, they briefly created a global cultural phenomenon. Families hiked up after work with thermoses; helicopters ferried visitors to the ridges; and the Icelandic blues-rock band Kaleo hauled instruments up the slope to film a live night performance of their single "Skinny" with incandescent lava fountaining directly behind the microphones.
Yet that intimacy also bred reckless stunts. By June 2021, "crust walkers" were climbing past warning signs to pose inside active surge channels or stroll across the blackened surface of cooling flows (High North News). What looks from a ridge like solid asphalt is in reality a brittle rind of volcanic glass bridging hollow drainage tubes where trapped interior heat remains hundreds of degrees Celsius for years. Icelandic authorities, including the Environment Agency (Umhverfisstofnun), SafeTravel.is (operated by ICE-SAR), and Visit Reykjanes): strictly prohibit walking on the lava fields: new lava enjoys special legal protection under the Nature Conservation Act, thin shelly pāhoehoe crust can collapse without warning under a boot, and if someone breaks through into a superheated cavity or toxic gas pocket, mounting a safe rescue may itself be impossible.
You do not need to step onto the lava to know that the rock is still alive. Pause on the ridge above Geldingadalir or Meradalir on a windless winter afternoon when the air drops to minus ten degrees Celsius, and a continuous, delicate chorus of snaps, clicks, and high-pitched chimes rises from the basin floor, like porcelain teacups or a crystal chandelier shattering in slow motion (Noise From Iceland). Where ponded basalt exceeds thirty meters in thickness, the insulated core stays superheated while frigid air shrinks the outer silicate shell, fracturing volcanic glass crystal by crystal. Any crust that is clicking is actively contracting and shifting.
That same residual heat drives a quieter atmospheric hazard in the valley bottoms (Veðurstofa Íslands). On calm days when wind speeds drop below five meters per second, escaping volcanic gases pool inside low-lying basins and craters (USGS: Volcanic Gases; IVHHN). Carbon dioxide (CO2) is colorless and odorless; heavier than cold air, it collects silently in depressions and can cause rapid asphyxiation without any visual or olfactory clue. Sulfur dioxide (SO2) is a colorless gas with a sharp, pungent, irritating odor (like a struck match) that stings the eyes and throat and can react in the atmosphere to form sulfate aerosols, sometimes seen hanging over the valleys as a faint bluish haze, while hydrogen sulfide (H2S) near warm fumaroles smells of rotten eggs at low levels but rapidly deadens the sense of smell at dangerous concentrations. Never rely on visible haze, steam, or smell alone to judge whether air is safe: a lack of visible haze or odor never proves a depression is clear of lethal gas.
If you plan to hike the ridges, remember that access across the Reykjanes eruption zone is dynamic (SafeTravel.is; Visit Reykjanes: Hiking and Parking). Both official trailhead parking lots, Parking P1 (Geldingadalir) and Parking P2 (Stóri-Leirdalur, 63.8587, -22.2786), are located along coastal Route 427 (Suðurstrandarvegur) east of Grindavík. When open, Path A climbs from P1 past the overrun 2021 Nátthagi barriers to viewpoints over the 2021 Geldingadalir and 2022 Meradalir fields (~6–8 km one way / ~12–16 km round trip, taking 2–2.5 hours each way); Path C climbs from P2 up the Langihryggur ridge (~4 km one way); and Path E leads from P2 on a strenuous 18–20 km round-trip trek (5–6 hours of hiking) to the 2023 Litli-Hrútur site. Because seismic swarms, magma accumulation beneath Svartsengi, gas drift, or weather can close roads and trails at short notice, always check live official updates on SafeTravel.is, Umferðin (umferdin.is), Veðurstofa Íslands (en.vedur.is), and Loftgæði (loftgaedi.is) before setting out. Stay on the high wind-swept ridges, look down across the rust-red iron of 2021 and the charred moss ring of 2023, and remember how much history, from Ísólfur's vanished sheep hollow to the 1943 bomber in the fog, now rests inside and beside that clicking stone.
A STORY. NOT A GUIDE.
ICELAND. TOLD.
Frequently Asked Questions: Fagradalsfjall, Meradalir & Litli-Hrútur
Is Fagradalsfjall still erupting, and how is it different from the Grindavík eruptions?
The Fagradalsfjall volcanic system is currently dormant following its three "Trilogy" eruptions at Geldingadalir (March–September 2021), Meradalir (August 2022), and Litli-Hrútur (July–August 2023). Those three eruptions were fed by deep mantle and near-Moho reservoirs (9–20 km depth) into enclosed, unpopulated mountain valleys. By contrast, the destructive eruptions that began in late 2023 along the Sundhnúksgígar crater row 5 km to the west tap a shallow crustal magma sill (4–5 km depth) directly beneath Svartsengi and Grindavík (Goldschmidt 2025).
Why does the cooled lava at Fagradalsfjall make a clicking or breaking-glass sound?
In ponded lava basins such as Geldingadalir and Meradalir where the basalt is more than 30 meters thick, the insulated interior core stays superheated for years while cold subarctic air chills the outer glassy rind. Differential thermal contraction causes the surface silicate crust to micro-fracture continuously, creating a high-pitched snapping and tinkling sound like breaking glass (Noise From Iceland).
Which hiking trails and parking lots serve Fagradalsfjall, and how do I check current access?
Both official parking lots, Parking P1 (Geldingadalir) and Parking P2 (Stóri-Leirdalur, 63.8587, -22.2786), are situated along coastal Route 427 (Suðurstrandarvegur) east of Grindavík (Visit Reykjanes: Hiking and Parking; SafeTravel.is). When trails are open, Path A from P1 (~6–8 km one way / ~12–16 km round trip, 2–2.5 hours each way) overlooks the 2021 Nátthagi barriers, 2021 Geldingadalir craters, and 2022 Meradalir flow; Path C from P2 (~4 km one way) climbs Mt. Langihryggur for a panoramic view across the 2021–2023 lava fields; and Path E from P2 (18–20 km round trip, 5–6 hours total) is a strenuous hike to the 2023 Litli-Hrútur site. Walking on the lava crust is strictly prohibited, and neither visible haze nor smell reliably warns of colorless, odorless CO2 or colorless, pungent SO2 gas in low basins (USGS: Volcanic Gases). Because volcanic unrest, gas pollution, or weather can close roads and trails at any time, always verify current official guidance on SafeTravel.is, Umferðin (umferdin.is), Veðurstofa Íslands (en.vedur.is), and Loftgæði (loftgaedi.is) before travelling.
