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How do underground wildfires burn and how are they extinguished?

Underground wildfires smoulder in peat and coal long after surface flames are gone, and they are hard to put out.

Updated 2 hours ago4 min readVersion 2
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Covers: The science of smouldering combustion in organic soils such as peat and in coal seams, why these fires persist and spread underground, and the suppression methods used, from water and smothering to excavation and barriers. Does not cover ordinary surface wildfires or firefighting tactics for above-ground fires.

Also answers: How do underground fires burn? · What are underground wildfires and how are they put out? · How are peat fires extinguished? · Why do underground fires keep burning?

A young pine tree in the foreground of a dark peat bog landscape
Photo: Jevgeņijs Grigorjevs

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Fill in the blank: ?% of the 2025 Scottish megafire's emissions that came from peat combustion

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The short answer

Interpretation AI-prepared starting map

Underground wildfires are smouldering fires that burn in carbon-rich material beneath the surface — peat soils and coal seams — rather than as open flame. They can persist long after visible flames are gone: after the July Cairngorms wildfire, "hot spots can continue to burn beneath the earth" (BBC News). In the 2025 Scottish megafire, peat combustion contributed nearly 85% of total emissions, with 38,600 MgC emitted (range 25,200–119,000 MgC), and such peatlands "can require decades to centuries to recover" (Schoenecker et al., Nature Geoscience). Suppression is difficult: even heavy natural snowfall could not put out a shallow smouldering peat fire, and a snow layer had to reach 9 ± 1 cm at subzero temperatures to extinguish it (Qin et al.). For coal, monitoring relies on indicator gases such as carbon monoxide, and machine-learning models are being developed for early warning of spontaneous combustion in mine goaf areas (Wu et al.).1234

What this rests on5 independent sources
  • Evidence 18
  • Interpretation 1

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In brief

  1. Underground wildfires smoulder in peat and coal and can keep burning long after surface flames are gone.1

    Evidence-backed
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  2. Peat fires can dominate emissions: in the 2025 Scottish megafire, peat combustion was nearly 85% of 38,600 MgC emitted, and recovery takes decades to centuries.2

    Evidence-backed
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  3. Cold and snow are weak suppressants: heavy snowfall failed to stop a shallow peat fire; about 9 cm of snow at subzero temperatures was needed to extinguish it.3

    Evidence-backed
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  4. Detection and early warning matter: drones find underground hot spots, and gas-based models predict coal spontaneous combustion within about 0.5–7% of monitored values.14

    Evidence-backed
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  5. Coal-mine response robots help rescuers but lack established design and deployment guidelines.5

    Evidence-backed
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At a glance

The picture in numbers

Live · updated just now

2025 Scottish megafire study

85%

85 in every 100

of the 2025 Scottish megafire's emissions that came from peat combustion2
Peat combustion emissions, range 25,200–119,000 MgC

38,600 MgC

carbon emitted by the 2025 Scottish megafire2
Outdoor experiments at subzero temperatures

9 cm

snow depth needed to put out a shallow smouldering peat fire3
CS-RF model at one coal mine's goaf

0.5–7%

0lowhigh

The high estimate is 14 times the low one.

how close the coal-fire prediction model stayed to monitored values4

The evidence behind it

5 sources
  • Reviews of many studies1
  • Other studies and data3
  • Background1

Published in 2025 and 2026

Sources on this page by kind and year
SourceKindYear
How drones are hunting fires hidden beneath the CairngormsBackground2026
Widespread peat carbon losses driven by the 2025 Scottish megafire.Other studies and data2026
Impact of Snow on Underground Smoldering Wildfire in Arctic-Boreal Peatlands.Other studies and data2025
Robots in mine search and rescue operations: a review of platforms and design requirements.Reviews of many studies2026
Prediction Model for Indicator Gas Concentration of Coal Spontaneous Combustion in Goaf Areas based on CS-RF.Other studies and data2026

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What it means for you

Which fits you?

Pick the situation closest to yours. Each answer says what it rests on.

If you are trying to put out a shallow smouldering peat fire in cold conditions

expect natural snowfall to fail; a snow layer of roughly 9 cm at subzero temperatures was the minimum that extinguished it in experiments, by drawing heat from the burning front.3

Evidence-backed

If surface flames at a peatland fire have died down

treat the fire as possibly still burning underground and look for hot spots, as drones were used to do after the Cairngorms wildfire.1

Evidence-backed

If you are assessing the climate impact of a peatland fire

account for peat combustion separately: it was nearly 85% of emissions in the 2025 Scottish megafire, and recovery can take decades to centuries.2

Evidence-backed

If you are monitoring a coal mine for spontaneous combustion

carbon monoxide is a usable indicator gas, and a CS-RF model predicted it within 0.53–6.91% of on-site values at one mine's goaf.4

Evidence-backed

If you are planning robot use in a coal-mine emergency

expect to make your own design and evaluation judgements, because comprehensive guidelines for these platforms have not been established.5

Evidence-backed

The full story · 2 chapters

01

How underground fires burn and why they persist

AI summary:Underground fires smoulder in peat and coal, persist after surface flames die, resist cold and snow, and are tracked by emissions and gas monitoring.

Evidence-backed

Evidence-backed: Underground wildfires smoulder in organic material rather than flaming at the surface. In peatlands, drier and warmer climates have allowed fires to burn carbon-dense peat; in the 2025 Scottish megafire, peat combustion contributed nearly 85% of total emissions, and the authors note such peatlands can take decades to centuries to recover.2

Evidence-backed

Evidence-backed: Persistence is the defining feature. After the July Cairngorms wildfire, the dramatic flames disappeared but hot spots continued to burn beneath the earth — the reason drones are being used to hunt them.1

Evidence-backed

Evidence-backed: Cold and snow do not reliably stop smouldering. In outdoor experiments at −5 ± 5 °C, even heavy natural snowfall (up to 1.1 mm/h water equivalent, or 7.9 mm over 24 h) could not suppress a shallow smouldering peat fire; a snow cover had to reach 9 ± 1 cm to extract enough heat from the burning front to extinguish it, a threshold confirmed in larger 1.5 × 1.5 m field demonstrations.3

Evidence-backed

Evidence-backed: In coal, spontaneous combustion is tracked through indicator gases. A hybrid model (Cuckoo Search–optimised Random Forest) predicting carbon monoxide concentration in the goaf of the 4427 working face at Tiejishan Coal Mine reduced RMSE by 11.85% and MAPE by 23.83% versus a plain Random Forest, cut training and prediction times by 74.83% and 31.43%, raised R2 by 11.97%, and stayed within 0.53–6.91% of on-site monitoring values.4

02

Suppression and response methods

AI summary:Suppression is limited: snow needed about 9 cm at subzero temperatures to extinguish a shallow peat fire, while drones, gas models and robots aid detection and response.

Evidence-backed

Evidence-backed: Water and smothering are the intuitive tools, but the snow experiments show the limits of adding water or cold cover: natural snowfall alone failed to extinguish a shallow peat fire, and only a sustained snow layer of about 9 cm at subzero temperatures did so by pulling heat from the burning front.3

Evidence-backed

Evidence-backed: Detection supports suppression: drones are being used to find hot spots still burning beneath the ground after surface flames are gone, as in the Cairngorms.1

Evidence-backed

Evidence-backed: For coal-mine incidents, robots are used to enter areas unsafe for human rescuers, locate trapped workers and collect data; the review notes that harsh underground conditions make these platforms complex and that comprehensive design and deployment guidelines have not been established, so developers rely on their own judgement.5

Evidence-backed

Evidence-backed: Early warning for coal spontaneous combustion rests on gas monitoring: carbon monoxide concentration in goaf areas can be predicted with the CS-RF model to within roughly 0.5–7% of monitored values, supporting faster, more accurate alerts.4

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Quick questions from connected pages

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What to remember

Try to recall each hidden figure before you reveal it. Remembering, not rereading, is what makes it stick.

  1. Peat fires can dominate emissions: in the 2025 Scottish megafire, peat combustion was nearly of 38,600 MgC emitted, and recovery takes decades to centuries.

  2. Cold and snow are weak suppressants: heavy snowfall failed to stop a shallow peat fire; about cm of snow at subzero temperatures was needed to extinguish it.

  3. Detection and early warning matter: drones find underground hot spots, and gas-based models predict coal spontaneous combustion within about of monitored values.

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a large plume of smoke billows into the skyUp nextHow do wildfires burn underground and how are they extinguished?How do wildfires burn underground, and how are they extinguished?

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  1. 1
    How drones are hunting fires hidden beneath the Cairngorms
    BBC NewsPublished Oct 10, 2026Checked Oct 10, 2026
    “Dramatic flames from the huge Cairngorms wildfire in July have disappeared - but hot spots can continue to burn beneath the earth.”
  2. 2
    Widespread peat carbon losses driven by the 2025 Scottish megafire.
    Nature geoscience (Schoenecker et al.)Published May 20, 2026Checked Oct 10, 2026
    “Drier and warmer climates have allowed fires to increasingly burn carbon-dense peatland ecosystems. Here we document a 2025 Scottish megafire in the UK, which spread rapidly and burned severely across peatlands in Scotland with anomalously low soil moisture, emitting 38,600 MgC (25,200-119,000 MgC). Peat combustion contributed nearly 85% of total emissions, suggesting drier climates increase fire emissions from peat, which can require decades to centuries to recover.”
  3. 3
    Impact of Snow on Underground Smoldering Wildfire in Arctic-Boreal Peatlands.
    Environmental science & technology (Qin et al.)Published Feb 6, 2025Checked Oct 10, 2026
    “Despite the critical role of fire-snow interactions in these processes, our understanding of them remains limited. Herein, we conducted small-scale outdoor experiments (20 × 20 × 20 cm3) at subzero temperatures (-5 ± 5 °C) to investigate the impact of natural snowfall and accumulated snow layers (up to 20 cm thick) on shallow smoldering peat fires. We found that even heavy natural snowfalls (a maximum water equivalent snowfall intensity of 1.1 mm/h or a 24 h accumulated snowfall water equivalent precipitation of 7.9 mm) cannot suppress a shallow smoldering peat fire. A thick snow cover on the peat surface can extract heat from the burning front underneath, and the minimum thickness of the snow layer to extinguish the peat fire was found to be 9 ± 1 cm at subzero temperatures, agreeing well with the theoretical analysis. Furthermore, larger-scale field demonstrations (1.5 × 1.5 m2) were conducted to validate the small-scale experimental phenomena. This work helps us to understand the interactions between fire and snow and reveals the persistence of smoldering wildfires under cold environments.”
  4. 4
    Prediction Model for Indicator Gas Concentration of Coal Spontaneous Combustion in Goaf Areas based on CS-RF.
    ACS omega (Wu et al.)Published Aug 31, 2026Checked Oct 10, 2026
    “It proposes a hybrid prediction model that optimizes the Random Forest algorithm using the Cuckoo Search algorithm. This approach aims to overcome the randomness and limitations associated with manual parameter tuning in the Random Forest algorithm. Using data from the goaf of the 4427 working face at the Tiejishan Coal Mine as a case study, and with carbon monoxide concentration as the prediction target, the model's applicability, superiority, and reliability were validated. The results showed that through adaptive global optimization, the CS-RF model significantly improves both prediction accuracy and efficiency. Compared to the RF model, the root-mean-square error (RMSE) and mean absolute percentage error (MAPE) were reduced by 11.85% and 23.83%, respectively. Training and prediction times were reduced by 74.83% and 31.43%, respectively, and the coefficient of determination (R2) for the linear fit increased by 11.97%; the error range relative to actual on-site monitoring values was 0.53%-6.91%. This study provides a new technical approach for the precise, rapid, and intelligent early warning of coal spontaneous combustion in coal mines.”
  5. 5
    Robots in mine search and rescue operations: a review of platforms and design requirements.
    Frontiers in robotics and AI (Bakzadeh et al.)Published Aug 5, 2026Checked Oct 10, 2026
    “Due to the harsh conditions during an underground mine disaster, robots can be of great assistance to rescue teams by entering areas that are unsafe for human rescuers, locating trapped workers, and collecting valuable data. The design and implementation of coal-mine rescue robots are characterized by great complexity because they encompass a great range of components and requirements. However, comprehensive guidelines for the design and deployment of robots in harsh underground environments have not been established. As a result, the developers of coal-mine rescue robots (CMRRs) must exercise their own judgment on the development and evaluation of the platform functionalities. This survey attempts to review design and functionality requirements based on the common practices and lessons learned from the existing CMRRs with the aim of facilitating future research and development on coal-mine search and rescue robots. An updated overview of the documented CMRRs of the last 3 decades showcases the intricate relationship of the common design considerations for CMRR design.”

How it changed

Published 1 time since Oct 10, 2026.

  1. Version 2Oct 10, 2026Live now

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  • Do the snow and water thresholds found for shallow peat fires hold for deep or large peat fires, and what actually extinguishes them?

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  • Which methods reliably extinguish burning coal seams, as opposed to detecting or predicting them?

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  • How long do burned peatlands take to recover carbon stocks, and what does recovery depend on?

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