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 50oF and
the following nighttime temperatures went to 20oF 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.
Fascinating. Love the ice designs, too.
ReplyDeleteThanks, Lois. You should enjoy all the ice and freezing weather while you can. I doubt that it will be able to follow you to Florida.
ReplyDeleteWhat a fascinating post. I was very curious about areas where rocks seem to have dropped down in a trail. In fact the rocks didn't "drop" The ground moved up. Your explanation is very helpful.
ReplyDeleteThanks, Sybil. I'm glad you found this interesting.
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