15-6 InSAR Shows Extensive Subsidence of Agricultural Land in New Zealand

Session: Integrated Digital Workflows in Geoscience: Mapping, Marine Exploration, and Machine Learning

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Abstract:

Historically, New Zealand was dominated by forests and wetlands below the alpine treeline.  However, approximately 1000 years of Polynesian and European settlement have resulted in the loss of nearly three-quarters of original forest cover, with agricultural development playing a significant role in this transformation through wetland drainage and land conversion to pasture. Our findings utilise InSAR to show that subsidence is occurring across large areas of agricultural land in Waikato and Southland, particularly in landscapes that were historically wetlands but have since been converted for agricultural use.  Subsidence is also present across the more arid Canterbury Plains.  In contrast, towns, rivers, and protected wetlands show little to no subsidence.  In low-relief farmland, a variety of agricultural practices including drainage, tillage, irrigation, livestock grazing, and mechanised compaction, lead to subsidence through distinct mechanisms such as soil densification, oxidation (causing CO₂ emissions), and aquifer compaction.  Additionally, downslope creep on east and west-facing mountain slopes in Southland and Canterbury is likely to have been exacerbated by the clearance of deep-rooted vegetation for pastoral agriculture.  These observations have important implications for a variety of environmental issues, including water quality, soil and aquifer compaction, CO₂ emissions, flooding, erosion, and landslide mitigation.

Geological Society of America Abstracts with Programs. Vol. 58, No. 2, 2026

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