Certain patterns of stones can form in frosty, rocky landscapes. This new study shows that needle ice spikes are groundwater-based ice spikes that rise from the earth can create these formations.
Researchers used both computer models and lab experiments to demonstrate how needle ice can shift soil particles and small rocks into patterns. This pushes them from below to slightly alter their positions.
Because needle ice forms more readily on bare ground patches, stones that are already present are slowly consolidated to create stunning patterns that stretch across the landscape from Norway to Hawaii.
"This kind of selective growth involves interesting feedbacks among the size of stones, soil moisture, and the growth of ice needles," said Bernard Hallet, University of Washington geologist.
The idea that needle ice can create patterns from stones dates back to decades. However, the researchers conducted their own experiments to determine how these formations came together. They then created a computer model that could replicate the process.
The experimental setup consisted of a square of wet soil measuring just over 1 foot (0.3 m) in area, with stones evenly distributed on its surface. The setup was then subjected to 30 freeze-thaw cycles, which represented the changing temperatures of day/night.
The resulting videos, including the one above, show that pattern formation can occur quickly and within 30 freeze-thaw cycles. How patterns form depends on the concentration of stones, ground slope, and height of the ice needles.
Hallet says that the videos are quite striking and show that the ice simply rises and pushes stones to the side in one cycle. These experiments, and the ability of the people involved to analyze the results, have given us much more concrete, quantitative descriptions of these features.
Researchers also linked their study to models of phase separation. The concept of two distinct parts emerging from one can be helpful in analysing cell structure, gravitational fluids and ecological systems.
This research extends beyond our planet. Scientists are also analyzing patterns that can be seen on Mars' surface. These patterns could reveal what's going on in the Martian environment.
Based on the initial concentration, two computer models predict stone distribution. (Li et al., PNAS 2021)
The team believes that needle ice patterns and local temperatures are closely linked to each other, which means that we might be able to understand how our planet responds to rising temperatures by studying the shifts in rock formations over time.
In their paper, the researchers write that phase separation theory is a key source of valuable insight into ground patterns in cold areas and its potential value in signaling significant changes in ground conditions due to the warming climate.
The research was published in PNAS.