What's that crunching beneath your feet? Is it frozen ground? Ice crystals? Crumbly snow? Does an uncommon glimmer catch your eye? Take a closer look. Needle ice may be underfoot!
Walking on needles sounds like a dangerous thing to do, but not when you're talking about needle ice.
Needle ice is a fascinating frozen formation caused by groundwater pushing up from beneath the soil and freezing at the surface. Mini, needle-shaped ice columns seem to grow out of the ground!
Ice segregation
Generally, soil will have the same amount of moisture throughout. Think about wet soil being a sponge soaked with water and dry soil being a dry sponge.
Words to know
Capillary: A tube that has a diameter of hairlike thickness.
Groundwater: Water held underground in soil or in pores and crevices in rock.
Segregate: To set apart, isolate or divide.
Sometimes, though, soil moisture will separate itself from the rest of the soil. Moisture can migrate to certain sections underground and freeze. Within a mix of soil particles, there could be a section of water that is segregated from the rest of the soil.
Without ice segregation, moisture in the soil freezes in tiny crystals that are evenly spaced throughout the soil. With ice segregation, water can freeze in columns.
Capillary action
If you spill water and put a sponge on top of the mess, the water defies gravity and is soaked up into the sponge. This is capillary action at work!
Moisture in the soil works in a similar way. Capillary action causes water to rise through the soil to the surface. This is the way plants get water through their roots. Ice needles grow up from the soil thanks to capillary action.
Try this! Take a dry paper towel and hold it from the top, dipping the bottom corner into a bowl of water. What happens to the water? What happens to the paper towel? How high does the water creep up the paper towel?
The right conditions
For needle ice to form, the right conditions must be present.
Moisture: Soil must have high moisture levels due to precipitation. If it rains or if a lot of snow melts right before a sharp drop in temperature, there is a chance needle ice can form.
Texture: The soil has to be just the right amount of compact. Soil must be loose enough to allow moisture to travel freely throughout. But if the soil is too loose, capillary action may not occur. If the soil is too compacted, needle ice does not have enough space to form.
Temperature: Winter weather is unpredictable. One day it is warm, the next everything is frozen solid. This is the perfect formula for needle ice. Air temperature changes more easily than ground temperature. Air can be warm one day and freezing the next, but the ground takes much longer to change temperatures. Even if the air is freezing, there might still be water flowing underground.
For needle ice to form, the unfrozen ground must be above 32 degrees Fahrenheit. This allows the moisture in the soil to stay liquid and move around underground. But the air temperature must drop below freezing, less than 32 degrees. When the water arrives at the surface thanks to capillary action, it will freeze when it hits that freezing cold air.
Put it all together now!
Ice segregation, capillary action, moisture, soil texture, above-freezing temperatures below ground and below-freezing temperature above ground all must align in just the right way for needle ice to form.
Log jam: Needle ice formation
Capillary action causes groundwater to be pulled to the surface, where it freezes due to cold air temperatures. This free-flowing groundwater is repeatedly pulled to the frozen surface and freezes as more groundwater is pulled up. This starts to cause a frozen-water ice backup.
When water freezes, it expands. So, as the liquid water butts up to the already frozen ice pillars, it freezes on contact. Pushing upward, the water freezes, taking up extra space, and pushes frozen tiny tubes through the ground. As more ice is pushed to the surface, capillary action pulls more moisture up from underground. Ice needles seem to grow from beneath the soil.
Where and when to look
A warm, wet, sunny day followed by a freezing evening is your best opportunity to find needle ice. Check areas with bare soil or dirt trails and areas with loose mulch or dirt.
Remember all the requirements needed for needle ice. If the conditions are perfect, go on a needle ice scouting mission. You might just get lucky and happen upon some while you are out and about on a brisk winter hike. Listen carefully for loud crunchy ground beneath your winter boots. Look carefully. You could be in for a real treat — uniquely beautiful needle ice may be underfoot!
There is always something new to learn when you are out in nature. Always keep your eyes peeled; you might just discover a wondrous phenomenon.
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