Mantle-derived gases can seep to the surface before a volcanic eruption, but detecting them is difficult when emissions are weak. We used seismic noise from individual stations at Cumbre Vieja Volcano, La Palma, to monitor shallow gas accumulation being modulated by atmospheric cycles. We find clear links between pressure variations and gas release, with a marked increase months before the 2021 eruption, highlighting potential for early warning and hazard assessment.