Freeze and Thaw

Blue Jay Barrens has been riding the temperature rollercoaster because of a seemingly never ending parade of small storm systems out of Canada that pass through about every three or four days.  Temperatures soar in advance of each storm and plummet following each departure.  That translates into a pattern of freezing and thawing of any exposed water.  Even the hilltop barrens, known for their extremely hot and dry conditions, are not immune to these actions.

Soil does not freeze, but the water within the soil does.  Under certain conditions, the freezing water causes a phenomenon known as Frost Heave, which transforms the smooth soil surface into a rough terrain of sharp peaks and valleys.  The effects are most dramatic when moist, unfrozen soil with high silt content is subjected to sudden below freezing temperatures.  We have had several occasions this winter where daytime temperatures were above 50^oF and the following nighttime temperatures went to 20^oF or lower.

As temperatures drop to the freezing point or below, surface moisture begins to freeze.  As water freezes in the soil, the soil becomes drier and the water lost to freezing is replaced by water rising from below through capillary action.  Upon reaching the base of the previously formed ice crystals, the water freezes and pushes the ice upward.  Soil trapped in the ice is also moved upward, forming tall pillars.  Plants caught by this action are often lifted right out of the ground.  The soil falls back into place when it thaws, but the plants are often left exposed on the surface.

Soil pillars can sometimes get several inches high.  This mixing action is a common way for seeds to get buried to a suitable depth for germination. 

When moisture is abundant and the freezing point is near the surface of the soil, you can get ice columns that contain very little soil.  This is commonly referred to as Needle Ice.

At this site, the surface froze quickly.  Ice columns began forming beneath that frozen layer and lifted the entire mass as a single unit.  Stones were not affected by this action and remained in their original positions.  The stones had the initial advantage of not cooling as quickly as the surrounding soil.  Then they were able to channel heat from the warmer soil they rested upon.  If the cold lasted long enough, the freeze point would drop lower into the soil and the stones could then be lifted.  In this instance the freezing lasted for only one night and the morning sunlight quickly thawed the soil.

The freezing and thawing is also having a disruptive impact on exposed rock layers. 

The Blue Jay Barrens bedrock was previously fractured by a prehistoric meteor impact.  These tiny cracks allow water to enter the rock slabs.  The water expands as it freezes and separates the rock layers.

When the ice thaws, the loosened rock falls down the slope.

The creek water freezes, but that generally occurs with no negative impacts.

The actions of freezing and thawing in the creek are more conducive to works of art than to damage.  Thin layers of ice form and are left suspended above a slowly dropping water level.

Periods of freezing temperatures add long, sharp crystals to the existing ice.

Warmer temperatures soften the crystals by blunting points and rounding edges.

The result can be a wild collection of varied forms.

One interesting phenomenon could not be adequately captured in a still image.  Then I remembered that my camera had video capability, so I proceeded to make my first ever video creation.  As water moves beneath the overhanging ice, surges in the creek flow cause it to periodically make contact with the ice.  The cohesive qualities of water allow it to keep its contact with the ice while maintaining a short column connecting the ice and the creek.  This contact is maintained as the water scoots on downstream, producing the dark image seen from above.  The violet color is the result of my inability to change the video settings on the camera.  I guess I’ll have to read the manual before making any more videos.  The video actually looks better when viewed on YouTube.  You can check it out there by clicking on http://youtu.be/DJA1EtSIcE8.

Hardship on a Bare Slope

My first impression upon seeing these pink strands arching from the ground was one of electric wires. Oh no! Blue Jay Barrens is a robot. That would explain why things here are just a little bit odd. Of course, these are not wires at all. They are a natural part of Blue Jay Barrens’ organic component.

The pink strands are exposed roots of a Gray Goldenrod. The basal rosette of healthy green leaves can be seen clustered in the center the dead leaves from last season. This plant succumbed to a condition known as frost heave, the action of alternating freezing and thawing of the soil. Frost heave is most common when the soil is saturated. The water between soil particles freezes and expands, causing the soil particles to move apart and push upward. The ice locks around the roots and crowns of plants and if the roots are not strongly anchored, the plant is forced upward. When the ground thaws, the soil particles fall back and the plant roots are left exposed. Each successive freeze and thaw cycle pulls the roots a little bit further out of the ground.

This type of frost heave is not normally a problem on steep slopes where the water can quickly drain away and allow the soil to dry. This year was an exception because the weather patterns didn’t allow time for the ground to dry before freezing. A common occurrence this winter was a rainfall ahead of an approaching cold front, followed by strong winds and a plunge into sub-freezing temperatures. The cold wind hitting the slopes began the freezing process almost immediately.

Areas of bare ground are most susceptible to frost heave. Vegetative cover protects the soil by slowing the process of freezing and thawing. Growing among other plants also lends support and helps to anchor the root system more securely in the ground. Frost heave often results in the death of the plant, but in some cases the plant seems unfazed by its new situation. Gray Goldenrods will often develop new roots below the rosette of leaves and establish itself in its new location.

There are many variables that come into play to cause a plant to lift out of the ground. The presence of a little extra mulch or a more secure anchor for the root system could protect the plant from movement. Most of the Gray Goldenrods growing on this slope managed to stay in place during the changes in weather conditions.