Vertical movement of the land under a gauge from sediment compaction, groundwater and oil extraction, tectonics or rebound of the crust after ice sheets melted. A gauge on sinking land records faster relative sea level rise than the ocean alone; one on rising land may record falling sea level. GNSS stations beside tide gauges measure it directly so the ocean and land parts of the trend can be separated.
Vertical land motion at the station is minus 4 millimetres a year from the GNSS, which explains the steep trend.
Also heard as
- VLM
Related terms
Relative sea level trend
The long-term rate of change in mean sea level at a gauge, including both ocean rise and land motion.
NAVD
North American Vertical Datum: the geodetic height reference used for land elevations across the United States.
Bench mark
A permanent, stable mark of known height near a tide station that preserves the station's datums.
Leveling
Precise measurement of height differences between bench marks and the gauge or staff using a level and rods.