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Smoldering is the dominant combustion process in peat fire, releasing a large amount of carbon and smoke into the atmosphere. The spread of smoldering in peatland is a multi-dimensional process, which is slow, low-temperature, persistent, and difficult to detect. In this work, we investigate the upward spread of peat fire from the underground to the surface after forced ignition which is a relevant configuration but rarely studied. In the experiment, ignition is not possible if the igniter is deeper than 15 cm below the free surface, regardless of moisture content or density. Once ignited, the 1st-stage upward fire spread is initiated towards the free surface (opposed smoldering) with a peak temperature of 300 °C, leaving behind a char structure that does not collapse. Then, a 2nd-stage downward spread (forward smoldering) is activated with a peak temperature of 600 °C and regression of free surface. The upward …