A lawn bubble is a localized area of turf or sod that lifts noticeably above the underlying soil, creating a soft, dome-shaped bulge. This phenomenon signals an underlying issue where pressure or a void causes the turf layer to detach and rise. The lifted area can feel spongy or firm, depending on whether it is filled with gas, water, or air. Because the turf provides a relatively impermeable layer, it traps substances, causing pressure to build and the bubble to form. Investigating the nature of the bubble is necessary to identify the cause and determine the corrective action.
Gas Accumulation from Organic Decomposition
One potential cause for a lifting lawn is the accumulation of gas generated by decomposing organic material beneath the surface. This gas is primarily methane, produced by anaerobic bacteria that thrive in oxygen-deprived environments, such as saturated soil or deep layers of buried debris. Large quantities of buried wood, construction waste, or excessive thatch can feed these microbes, creating a substantial gas pocket over time.
The sod layer traps the gas as it rises from the soil, allowing pressure to build until it physically lifts the turf. This becomes serious if the gas source is a leak from a septic system or a broken sewer line, which can introduce methane or other noxious gases. If a bubble feels light and hollow near organic debris or utility lines, it may indicate a dangerous concentration of flammable gas that requires immediate professional assessment.
Lifting Caused by Hydrostatic Pressure
Turf lifting can also involve hydrostatic pressure, which is the force exerted by standing water. This occurs when the soil beneath the sod becomes completely saturated, often due to poor drainage, heavy rainfall, or a leak from a broken irrigation line. The water fills all available pore spaces and, because it is incompressible, begins to exert upward pressure on the overlying turf.
This process is most common in areas with underlying hardpan or clay soils, which do not allow water to drain quickly. The saturated soil and trapped water create a pressure differential that pushes the turf layer up, forming a water-filled blister that feels squishy when stepped on. Puncturing this type of bubble results in the release of water, confirming the cause is liquid saturation rather than gas buildup.
Voids from Structural Settlement or Buried Materials
Lawn bubbles can also form when a void is created beneath the surface, allowing the turf to slump or lift into the empty space. This happens after the decomposition of large, buried materials, such as tree stumps or construction debris, which rot away and leave a hollow cavity. The intact sod layer then bridges this void and may lift slightly, making the area feel hollow or unstable.
Another structural cause involves poorly compacted soil in old utility trenches, which can settle unevenly and create a subsurface depression. When sod is laid directly over non-degradable barriers like plastic sheeting or geotextile fabric, the turf roots cannot anchor properly. This shallow root system allows the entire layer of turf to be easily lifted, creating a bubble that is more a sign of poor installation than a deep soil problem.