The height of the lava column is a fundamental measure of open-vent volcanic activity, but little continuous long-term data exist to understand this parameter. The recent (2008-2018) lava lake activity at the summit of Kīlauea Volcano provides a unique opportunity to track and understand the processes that control lava level over timescales ranging from minutes to years. We review recently published data as well as analyze the long-term record of lava level at Kīlauea’s summit during 2009-2017. Longer timescale fluctuations, over days to months, have a strong positive linear correlation with ground deformation, suggesting they reflect pressure changes in the summit magma reservoir. Shorter timescale fluctuations, over minutes to hours, have an inverse relationship with spattering (i.e. outgassing) intensity at the lake surface – increased outgassing lowers the lake level and vice versa. Our analysis of the long-term lava level data thus confirms that lava level at Halemaʻumaʻu is controlled by these two types of processes: 1) those related to magma reservoir pressure changes (such as magma supply rate) and 2) shallow outgassing fluctuations (such as gas pistoning). Frequency filtering can isolate pressure- and outgassing-driven components of lava level change. Time series analysis indicates that there was no large, persistent periodicity in the lava level; a minor fortnightly oscillation might be related to Earth tides but was not continuously present. The remarkable correlation between lava level and deformation of the summit indicates that the lava lake acts as a reliable “piezometer”; tracking lava level over time may thus provide an indication of flank eruptive potential. We show that long-term interdisciplinary monitoring is necessary to discriminate the processes that control lava level.