Long Runout Landslides
in the Solar System

Scaling relationship between ridge wavelength and landslide deposit thickness

Longitudinal ridges are distinct morphological features that extend in the direction of movement of many long runout landslides. From morphometric analysis conducted on three case studies — the Coprates Labes landslide (Mars), the El Magnifico landslide (Earth), and the Tsiolkovskiy landslide (Moon) — it emerges that the wavelength of longitudinal ridges scales with the thickness of the landslide deposit.

The recurrence of this scaling relationship across three different planetary bodies suggests that the mechanism behind the formation of longitudinal ridges is independent of environmental conditions. Furthermore, this relationship agrees with ice-free experimental work on rapid granular flows, indicating the mechanism is also scale-independent.

Formation mechanisms: vibration-assisted and convection-type processes

Longitudinal ridges are commonly associated with long runout landslides emplaced on glaciers, where basal ice is thought to provide a low-friction surface enabling spread and tensile deformation. However, long runout landslides with longitudinal ridges also occur in ice-free environments — on the Moon, and in the northern Atacama Desert, Chile, under established hyper-arid conditions.

We conceptualise a vibration-assisted mechanism and a convection-type mechanism as a continuum dependent on lithology, event duration, and velocity. Both mechanisms rely on the same energy input: vibrations. A mechanical instability generating convection-style motion emerges when certain lithologies, velocities, and stresses cause the sliding mass to behave as a granular flow. Where this extreme instability does not emerge, pattern-forming vibrations within the sliding mass may instead dominate.

For more details:
Magnarini et al. (2019) Longitudinal ridges imparted by high-speed granular flow mechanisms in martian landslides.
Magnarini et al. (2021) Implications of longitudinal ridges for the mechanics of ice-free long runout landslides.
Magnarini et al. (2021) Scaling Relationship Between the Wavelength of Longitudinal Ridges and the Thickness of Long Runout Landslides on the Moon.

Implications for the hypermobility of the Light Mantle landslide

Evidence for long runout landslides on the Moon raises important questions about friction-reduction mechanisms on planetary bodies lacking atmosphere and surface water. The Light Mantle landslide's exceptional 5 km runout made it a primary geological target of the Apollo 17 mission, yet its hypermobility remains unexplained due to a lack of experimental support and scarce field data on the deposit's internal structures.

For the first time, we performed low-atmosphere (high-vacuum) friction experiments on lunar analogue anorthosite-bearing gouges to test the theoretical viability of thermally activated dynamic weakening mechanisms in lunar material, using the high velocity rotary shear apparatus SHIVA at the Istituto Nazionale di Geofisica e Vulcanologia in Rome.

Anorthositic material showed high dynamic shear strength with no evidence of dynamic weakening at conditions where it occurs in other materials. This suggests friction weakening mechanisms did not dominate the initiation of the Light Mantle landslide — other mechanisms must account for its exceptional runout distance.

For more details:
Magnarini et al. (2023) Friction Experiments on Lunar Analog Gouges and Implications for the Mechanism of the Apollo 17 Long Runout Landslide.

Microstructural clast observations: keys to interpreting Apollo 17 core samples 73001/73002

Microstructural observations of frictionally-modified material recovered after experiments reveal clast fabrics and morphologies previously described in the basal slip zones of large terrestrial landslides — specifically Clast Cortex Aggregates (CCAs), comprising a central clast surrounded by fine-grained fragments from broken edges.

Initial investigation of clasts from Apollo 17 sample 73002 (under the NASA ANGSA programme) reveals several clasts with fabric and morphology similar to those produced experimentally. This suggests that clasts within the Apollo 17 core samples may preserve information about mechanisms active during the emplacement of the Light Mantle landslide, though further analysis with other lunar samples is needed to distinguish landslide-related structures from other processes.

Read about the ANGSA work here

Icelandic landslides as analogues of martian landforms

On Earth, well-preserved long runout landslides with longitudinal ridges are far rarer than on Mars. Iceland is an exceptional exception: more than one hundred such landslides are identifiable there, representing the highest spatial density of these landforms on Earth. This either implies that longitudinal ridges are common but poorly preserved on Earth in general, or that Iceland's conditions at the time of landslide formation were particularly conducive to their development.

Studying this record offers an opportunity to investigate the formation mechanisms of hypermobile landslides and their link with past environmental conditions — with implications for both terrestrial hazard assessment and reconstruction of extra-terrestrial palaeoenvironments.

Beyond morphometric comparability, Icelandic landslides share structural behaviours with martian analogues, including splitting of longitudinal ridges and development of en-échelon features, confirming their value as planetary analogues.

For more details:
Magnarini et al. (2024) Long Runout Landslides with Associated Longitudinal Ridges in Iceland as Analogues of Martian Landforms. Earth Surface Dynamics 12(3), 657–678.

Kinematics of long-runout landslides on Mars

Soon