Sicily’s Niscemi Landslide in Focus: Revealing Long-Term Ground Deformation through InSAR
- Dr. Vishnu Yaragunda
- Feb 17
- 4 min read
In January 2026, a major landslide occurred near Niscemi in southern Sicily, where heavy rainfall associated with Storm Harry triggered the collapse of an approximately 4 km section of cliff.
The event developed rapidly at the surface, causing widespread damage to infrastructure and triggering the evacuation of over 1000 residents.
Using InSAR to detect historical ground motion trends
Using InSAR, Geofem analysed long-term ground deformation patterns to better understand the pre-failure conditions and the broader geodynamic framework surrounding the event.
Beyond the immediate failure, satellite-based ground motion measurements allow assessment of background deformation trends active in the area prior to the storm-triggered collapse.
Placing the landslides within a broader geodynamic context, Geofem conducted a Multi-Temporal InSAR (MT-InSAR) analysis using Sentinel-1 data.
The analysis focused on characterising long-term ground motion trends leading up to January 2026.
MT-InSAR analysis framework
Geofem processed Sentinel-1 SAR imagery in both ascending and descending geometry, covering the period:
12 January 2023 – 26 January 2026
From the combined datasets, we derived:
Mean Line-of-Sight (LOS) deformation velocities
Displacement time series at representative points
Decomposed vertical and east–west horizontal motion components
These products allow separation of long-term deformation behaviour from short-lived surface processes.
Observed deformation patterns
Ascending and Descending LOS Results
Both ascending and descending LOS velocity maps show spatially clustered deformation patterns, with mean velocities of selected scatterer points reaching approximately –13 to –14 mm/year in the most active zones.
Importantly, the strongest deformation signals are not distributed uniformly across the mapped landslide area identified in optical imagery. Instead, deformation is concentrated along one edge of the landslide boundary, while large portions of the interior appeared comparatively stable in the InSAR analysis in the months and years leading up to the collapse.
The observed deformation therefore represents a gradual mobilisation of the landslide rather than a simple, sudden landslide mass rupture. The areas of sliding progressively grew and merged into one large landslide event as ground stresses were redistributed from shearing masses to adjacent ground.
Vertical and horizontal motion decomposition
By combining ascending and descending observations, Geofem decomposed the deformation field into vertical and horizontal components.
Vertical motion
The vertical velocity map shows dominant subsidence, locally exceeding –7 to –8 mm/year, particularly near the deformation cluster adjacent to the landslide boundary. Time series indicate a near-linear downward trend throughout the 2023–2026 observation period, with no abrupt acceleration prior to January 2026.
Horizontal motion
The horizontal (east–west) component reveals lateral movement, with velocities up to ~9 mm/year in certain sectors. The spatial coherence and steady temporal evolution suggest slow movement rather than episodic movement.
Together, the vertical and horizontal components indicate persistent, multi-directional ground deformation, characteristic of slow-moving slope systems.
Consistency with EGMS observations (2019–2023)
To assess whether these deformation trends are recent or long-standing, the MT-InSAR results were compared with the European Ground Motion Service (EGMS) dataset, which spans 2019–2023.
Despite covering different time windows, both datasets show:
Comparable spatial deformation patterns
Zones of uplift and subsidence
Similar deformation patterns
In this context, the January 2026 landslides occurred within an already deforming landscape, rather than representing the onset of entirely new ground motion.
3D perspective on ground motion
A three-dimensional visualisation of deformation velocity further illustrates the extent of the deforming zone. The 3D view highlights:
Gradual spatial transitions rather than sharp displacement discontinuities.
A geometry consistent with long-term slope deformation processes.
This reinforces the interpretation of slow, progressive ground movement, rather than abrupt landslide-driven displacement.
The value of MT-InSAR for landslide contextual analysis
This case demonstrates the strength of MT-InSAR, not as a landslide “trigger detector”, but as a contextual monitoring tool.
Key advantages include:
Long-term deformation tracking
MT-InSAR captures millimetric ground motion over multi-year periods, revealing whether slopes are stable, creeping, or evolving over time.
Objective spatial coverage
Satellite-based ground motion observations provide wide-area coverage beyond individual landslide features, complementing optical imagery and in-situ measurements by capturing subtle surface deformation over large regions.
Risk-informed interpretation
Understanding background deformation helps distinguish between preconditioning processes and event-driven failures.
Ultimately, the strength of MT-InSAR lies in its ability to shift the perspective from reactive assessment to proactive understanding.
By revealing long-term deformation trends across entire landscapes, it provides the broader context needed to interpret landslide events not as isolated incidents, but as part of an evolving geodynamic process.
Integrating MT-InSAR into hazard assessment frameworks enables more informed decision-making, earlier risk identification, and a more resilient approach to managing vulnerable terrain in a changing climate.
Build resilience through insight. Get in touch with Geofem to integrate MT-InSAR into your hazard assessment and infrastructure planning framework.
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