Peatlands (bogs, mires, and moors) are wetland ecosystems where organic matter decomposes slowly due to waterlogged, low-oxygen conditions. Over thousands of years, this process creates thick layers of a dark, spongy material called peat. A peat fire is the combustion of this stored organic material, fundamentally altering the landscape and releasing accumulated matter into the atmosphere. Understanding the specific characteristics of peat and how it burns is necessary to comprehend the impact of these events.
The Composition and Flammability of Peat
Peat is partially decayed organic matter, primarily derived from plant material like mosses and sedges, accumulated in saturated conditions. Composed mainly of carbon, it has a high energy content similar to lignite coal. In its natural, undisturbed state, peat contains a water content exceeding 90% by mass, which effectively prevents ignition.
Water is the most important factor regulating peat’s flammability, acting as a natural fire suppressant. When the water table drops significantly, often due to drainage, drought, or human activity, the peat dries out and becomes susceptible to combustion. The probability of a peat fire increases substantially once the water table falls below 40 to 50 centimeters from the ground surface. This drying transforms the organic reservoir into a potent, readily available fuel source.
The Unique Behavior of Subsurface Smoldering
Once ignited, a peat fire is defined by slow, flameless smoldering combustion, distinct from the rapid, high-temperature flaming of a typical wildfire. Smoldering occurs when oxygen reacts directly with the solid fuel surface, propagating at roughly one centimeter per hour. This lower-temperature reaction, typically around 500 degrees Celsius, allows the fire to burn persistently while consuming the dense organic material.
The combustion front travels downward and horizontally through the porous peat layer, often deep beneath the surface and out of sight. This subsurface movement means the fire can burn without visible flames or a strong smoke plume, making detection challenging. A surface fire may transition into a smoldering peat fire if dry conditions allow heat to penetrate the ground. These fires can linger for months or years, sometimes referred to as “zombie fires,” spreading underground and resurfacing unexpectedly.
Extinguishing a Peat Fire
The deep, subsurface smoldering of a peat fire necessitates specialized suppression techniques that differ from traditional firefighting methods. The primary requirement is achieving deep saturation of the burning material, which traditional surface application of water or firebreaks often fails to accomplish. Firefighters must first accurately locate the combustion zone before applying water, since the fire moves beneath the surface.
Thermal imaging cameras are used to identify hidden hot spots and map the fire’s subterranean perimeter. Once located, water must be injected directly into the peat layer using high-pressure lances or specialized piercing tools that deliver water or a wetting agent deep underground. Other techniques involve constructing trenches using heavy machinery to physically remove the burning peat layer down to the mineral soil or water table. Soil compaction is also used to smother the fire by removing the air pockets necessary for oxygen.
The logistical challenge of fighting these fires stems from the immense volume of water required for saturation, which can be difficult to transport to remote peatlands. A significant volume of water per unit of peat is necessary for successful suppression. Traditional methods using surface hoses are inefficient because the water cannot penetrate the dense, organic matrix, highlighting the need for injection-based strategies.
Global Environmental and Health Hazards
The combustion of peat releases vast stores of carbon sequestered over millennia, making these fires a significant source of global greenhouse gas emissions. Peatlands store more carbon than all other vegetation types combined. Their burning releases large quantities of carbon dioxide and methane, contributing substantially to atmospheric warming. In some regions, the carbon released from peat fires in a single year can be equivalent to a large percentage of the total annual anthropogenic carbon emissions from that area.
Peat fires generate dense, persistent smoke that poses significant health hazards across vast distances. Smoldering combustion produces a higher proportion of fine particulate matter (PM2.5) than flaming fires. These microscopic particles can travel hundreds of kilometers and penetrate deep into the human respiratory system, causing or aggravating severe respiratory and cardiovascular issues. Peat smoke also contains a complex mixture of toxic compounds, including volatile organic compounds, carbon monoxide, and polyaromatic hydrocarbons, presenting a long-term public health risk.