Tag: Volcanic climate effects

A sediment core from a southern Swedish lake (Körslättamossen) shows that the Laacher See volcanic eruption in western Europe occurred roughly 150 years before the onset of the Younger Dryas cold spell (~12,900 years ago), separating the two events.

Researchers including Christopher Moore (University of South Carolina) analyzed the core and identified:

• Deeper layers with volcanic ash (tephra) from the Laacher See eruption (dated ~13,006 ± 9 cal BP in related work).
• A distinct younger layer (~6- 10 cm higher, modeled basal age ~12,861 ± 54 cal BP) containing micro spherules (tiny, melted particles) and platinum- rich nanoparticles, interpreted by the team as possible evidence consistent with an extraterrestrial impact or airburst (the Younger Dryas Boundary or YDB layer).
• Immediately above that, sediments recording a shift to colder, wetter conditions marking the start of the Younger Dryas.

This sequence challenges the idea that the Laacher See eruption directly triggered the millennium- scale cooling in central Europe and the Arctic. Volcanic climate effects typically last years to decades, not centuries, and the ~150-year gap means any direct forcing would have faded long before the cold period began.

The findings add to the long- running debate over Younger Dryas causes (ocean circulation changes, volcanism, or the impact hypothesis). The Swedish core expands the European record for testing these ideas by clearly separating the eruption, the particle- rich boundary layer, and the cooling onset in one continuous archive. The study was published in ScienceOpen Research (September 2026) and does not claim to prove an impact origin, other terrestrial processes remain possible, but it rules out treating the eruption and the cold spell as the same event.

This aligns with earlier revised dating of the Laacher See eruption (to more than a century earlier than previously thought), which already weakened direct links to the Greenland Stadial- 1 cooling.

The Laacher See eruption (LSE) was a major Plinian (and partly phreatomagmatic) volcanic event in the East Eifel volcanic field of western Germany (Rhineland- Palatinate), roughly 40 km south of Bonn. It formed the present- day Laacher See crater lake.

Key facts

• Date: Best current estimates place it at 13,006 ± 9 calibrated years BP (before AD 1950), based on dendrochronology and radiocarbon dating of trees buried by the pyroclastic deposits (Reinig et al., Nature, 2021). Some earlier or alternative estimates put it closer to ~12,880– 12,900 years BP; the precise timing remains slightly debated due to possible magmatic CO₂ effects on radiocarbon dates.⁠
• Size: Volcanic Explosivity Index (VEI) of 6 (comparable to the 1991 Pinatubo eruption). It erupted roughly 6- 6.3 km³ of magma (dense- rock equivalent), producing ~16- 20 km³ of tephra (ash, pumice, etc.). The eruption column reached at least 20 km high.⁠
• Composition: Strongly zoned phonolitic magma, highly evolved, crystal- poor phonolite early in the eruption, becoming more mafic and crystal- rich later.
• Duration: Occurred over a period of days to a few weeks, likely in spring.

Deposits and impacts

The Laacher See Tephra (LST) is divided into Lower (LLST), Middle (MLST), and Upper (ULST) units. Proximal deposits near the volcano are tens of meters thick. Distal ash spread across much of central and northern Europe in three main fans (northeast up to ~1,100 km, south up to ~600 km, and southwest).

Ash has been identified as far as southern Sweden, northern Italy, Poland, and parts of France and Belgium. It is one of the most important Late Glacial chronostratigraphic marker horizons in European lake, peat, and archaeological sequences.⁠

Local effects included:

• Widespread destruction of vegetation and wildlife within tens of kilometers.
• Temporary damming of the Rhine River, forming a large lake (~140 km²) whose later failure caused a catastrophic flood downstream.
• Significant sulfur release (estimates range from a few to >100 Mt), capable of producing short- term atmospheric cooling and environmental stress for years to decades.

Relation to the Younger Dryas

The eruption was long discussed as a possible trigger for the abrupt Younger Dryas cold period (~12,900- 11,700 years ago). High- precision dating now shows it occurred ~130- 150 years earlier than the onset of Younger Dryas cooling in both European and Greenland records.

Recent sediment- core work (including the Swedish Körslättamossen core) further separates the Laacher See ash from the Younger Dryas Boundary layer and the start of cooling, making a direct causal link unlikely. Volcanic cooling effects are typically short- lived, not multi- century.⁠

The Laacher See remains an exceptionally well- studied Late Pleistocene eruption and a key time- marker for synchronizing paleoclimate and archaeological records across Europe.

Stratigraphic separation of Laacher See Tephra and a discrete Younger Dryas Boundary fallout layer in southernmost Sweden

This is the open- access paper (or its published version) behind the recent University of South Carolina– led study: “Stratigraphic Separation of Laacher See Tephra and a Discrete Younger Dryas Boundary Fallout Layer in Southernmost Sweden”

Key findings (from the abstract and related reports)

• Site: Körslättamossen fen (southernmost Sweden).
• Stratigraphy (depths from the core):
  • Laacher See Tephra (LST / volcanic ash) at 288.5 cm (~13,006 cal BP).
  • Discrete Younger Dryas Boundary (YDB) fallout layer at 282- 279 cm (PGE- rich horizon containing micro spherules and platinum- group element, platinum-rich nanoparticles); basal age modeled at ~12,861 ± 54 cal BP.
  • Immediate overlying sediments record the shift to colder and wetter conditions at the start of the Younger Dryas.
• The volcanic ash lies 6– 10 cm below the YDB layer, corresponding to a temporal separation of roughly 150 years.

This is described as the first robustly dated Scandinavian record that clearly separates the three events stratigraphically and temporally:

1. Laacher See eruption,
2. Deposition of the discrete YDB fallout layer,
3. Onset of Younger Dryas cooling.

The authors argue this separation makes the Laacher See eruption an unlikely primary trigger for the Younger Dryas cooling (volcanic aerosol effects are typically short- lived).

The YDB layer’s micro spherules and elevated platinum- group elements are interpreted as consistent with a possible extraterrestrial (impact and airburst) origin, though terrestrial alternatives are acknowledged and the paper does not claim definitive proof of an impact.

Lead author: Christopher R. Moore (University of South Carolina / South Carolina Institute for Archaeology and Anthropology), with an international team.

A related preprint version appears under DOI 10.14293/PR2199.003441.v1 (or .v2) with the same title.

Full- text retrieval from the hosted- document page was unsuccessful in this session (possible access or loading issue), but the core results match the press coverage from the University of South Carolina and independent reports.

Journal: ScienceOpen Research, 2026

DOI: 10.14293/S2199-1006.1.SOR.2026.0004.v1

Provided: University of South Carolina

Publication date (Electronic): 30 September 2026

Authors: Christopher R. Moore, Simon A. Larsson, Mohammed Baalousha, Michael Bizimis, Mahbub Alam, Allen West, Malcolm A. LeCompte, James P. Kennett, Gunther Kletetschka, Julie Chouinard, A. Victor Adedeji, Timothy Witwer

Abstract

The temporal relationship between the Laacher See eruption (LSE), the Younger Dryas Boundary (YDB) layer, and the abrupt onset of Younger Dryas (YD) climate change has long been debated. The Körslättamossen fen in southernmost Sweden provides the first robustly dated Scandinavian record demonstrating that these events are clearly separated stratigraphically and temporally. The Laacher See Tephra (LST) layer at 288.5 cm (~13,006 cal BP) lies 6–10 cm below a discrete PGE-rich horizon (282–279 cm) marking YDB deposition, interpreted here as a 3-cm-thick impact fallout layer. This interval has an onset Bayesian-modeled age of 12,861 ± 54 cal BP, ~150 years after the eruption, indicating that the LST and YDB deposition represent separate events. Within this fallout layer, Fe–Si microspherules with dendritic quench textures peak at 282–281 cm, while maximum PGE-bearing nanoparticle mass occurs at 280–279 cm, consistent with delayed settling of submicron particles. LA-ICP-MS reveals Si-rich microspherules containing PGE-bearing microdomains but negligible Ni, Co, and Cr. These compositions indicate that the microspherules are dominated by terrestrial target material rather than meteoritic metal, while the associated PGE-rich microdomains and nanoparticle populations record a minor but detectable extraterrestrial component. Single-particle ICP-TOF-MS detects a sharp Pt anomaly with Pt-dominant elemental ratios (e.g., high Pt relative to Fe and Ir), consistent with the platinum enrichment reported in the YDB in the GISP2 ice core. Immediately above the fallout layer, a dark, organic-rich horizon records the abrupt hydroclimatic shift to cooler, wetter YD conditions. These observations document three stratigraphically distinct horizons: the LSE, a separate YDB fallout layer, and the near-synchronous onset of YD climate change, providing a well-constrained European stratigraphic framework for evaluating mechanisms proposed for the YD onset.