Simple lateral spread landslide models made with glass microbeads and shaking

By Philip S. Prince

Many aspects of geology are fundamentally related to material movement, but geologists can often only examine the final results of movement due to physical scale, time, and personnel safety. Earthquake-related lateral landslides are a good example – they create incredibly dramatic landscape damage, but filming one from a suitable vantage point during intense shaking is nearly impossible. Physical modeling of lateral spreads is also problematic because of the soil liquefaction involved; it is difficult to combine dry and wet granular media and keep them (and their properties) separate. An illustrative and completely dry side scatter model can be made with glass microbeads under a continuous sand pack, as I do by combining sand and flour. During shaking, the microbeads behave like a viscous liquid and deform the overlying sandpack. The pictures below show such a model that I recently made. I decorated the pre-slide scenery with Monopoly houses and hotels, which stuck in the center of the action.

Lateral scattering models made this way are purely conceptual and illustrative, but they look cool and reproduce details of ground deformation above a seismically floating horizon. A sandpack is constructed over a layer of glass microbeads, and the entire base plate underneath the model is shaken to cause the microbeads to “float to liquid.” Deformation of the cohesive sandpack above the microbeads is visually interesting, with complex arrays of scarps and rotated blocks, as seen below.

No effort is made to scale the shake; the model is simply shaken until the microbeads lose strength, presumably due to reduced sliding friction against each other under acceleration. The look in motion of these models is fun to watch and is the main takeaway from this post. The video linked below shows the model above, along with two others. The video shows the shakes and failures at 1/2 speed, which is a little easier to see.

While the shaking frequency and amplitude are exaggerated to get the desired result, the lateral spreads made using microbeads show some realistic details that are useful for students or non-geologists to see and connect to a formative process. Block rotation and tilting or sinking of structures within the spread is one such detail, as seen below.

I tried to match these to some of the Turnagain neighborhood photos from the 1964 Alaska earthquake, with acceptable results. The picture below is from the Atlantic, I think.

The model's lateral spreads also move with gravity and require very, very little tilt to do so. Tilting the bottom plate only a couple of degrees will result in downward flow. The models shown above used a slight (3 degree?) tilted setup and a layer of daylight microbeads (the model starts with a “bluff” under the houses) to create a highly directional spread. The overall appearance, along with the finer details, can be made to match photographs of real lateral spreads very closely.

Lateral spreads affecting the infrastructure can also be modelled. The experiments shown below induced lateral spreading under a model embankment. Again, with slight tilt or asymmetry, the spread that develops is directional. The arched scarps in the model spreads below turned out well.

These models constrained the microbeads in all directions, and they “slipped” significantly from side to side; this movement is easily visible in the video linked below.

The final geometry of these spreads was remarkably flat, with a gently raised toe arch and equally low slide-head camber. Head and toe reach this equilibrium geometry when the microbead layer was at its weakest.

Inducing lateral spreading under a symmetric embankment-type structure without slope produced a variety of results, but bidirectional spreading and toe compression are possible. Sloshing was a problem here too – see previous video link. Shaking in a single direction meant that the final result was related to the embankment's orientation to the direction of shaking.

I wanted these models to be compared to one of the more spread examples from the 2018 Alaska earthquake, where a road (Vine Road, I think) experienced bidirectional spreading with two compression years. Image below is from USGS My setup needs more work, but the potential is there…

The obvious drawbacks of these models are the lack of true pore-water-induced liquefaction and the excessive shaking and sloshing, but these models are easy to set up, easy to break down, and make the connection between shaking, distinct material behaviors and earthquake/slide-related landforms easy to appreciate. Vibrating the bottom plate can also produce a good result, but I have not constructed a rig to produce it. If anyone gives it a shot, let me know!

Philip Prince is a project geologist with Appalachian Landslide Consultants, PLLC, in Asheville, North Carolina. He also performs geologic mapping in the Virginia Valley and Ridge for the Virginia Department of Mines, Minerals and Energy. More posts related to his field experiences and remote sensing work can be found at princegeology.com.