Little Climates -- Part One
Nature Bulletin No. 478-A January 27, 1973
Forest Preserve District of Cook County
George W. Dunne, President
Roland F. Eisenbeis, Supt. of Conservation
-- Part One: Weather in the Soi.
Climate vitally affects our lives. Wherever we live, climate has largely
determined the plant and animal life in that region, the development of
civilization there and what people do. The climate of any region
represents its overall weather picture: the sum of its weather today,
tomorrow, and during past centuries. We are accustomed to think of
climate as a set of conditions occurring entirely in the atmosphere
above the earth's surface, and it may sound silly when we say that there
are climates underground -- little climates just as real as those above --
but it's true, There are special kinds of weather in the soil.
Land is not a solid wall. It is like a sponge. There are pores or channels
in it. It is a complex mixture of soil particles and air spaces. The spaces,
or pores and channels, vary with the type of soil. In sand they are tiny
pockets between the grains. In clays they are narrow or threadlike
spaces frequently occurring as deep twisting tubes that taper downward.
Weather from aloft can invade such pores or real air currents, fogs,
drizzles and snows.
Air currents in the soil move generally up and down. Air sinks into the
soil because it has weight and is pulled downward by gravity. It rises
underground when it is energized by heat and expands; it also rises
when it is shoved upward by other air or by water. It may escape above
the surface or, if the "push" is weak, into another part of the soil.
Weather conditions underground, such as fogs, drizzles and snows, are
created by air currents there and three forms of water. We are all
familiar with liquid water and with ice, the solid form, but there is a
third: vapor, which is the gaseous form. The latter occurs when liquid
water or ice are heated to the point where their tiny particles, filled with
energy, are expelled and streak away on separate courses. Widely
separated and invisible, they form vapor. If vapor is chilled -- its store
of heat energy is taken away -- the particles are brought together and
become visible as liquid water or ice.
Drizzles and moist fogs are two kinds of liquid water that result from
the cooling of water vapor, but a drizzle contains much larger particles
which we call "drops ll. Both occur and travel underground. They are
shoved around by subsurface air currents and are valuable sources of
moisture for plant roots. At night, sometimes, it is possible to shine a
strong flashlight into the cracks or large pores in a soil and glimpse an
underground fog or drizzle.
Ice fogs and snow also occur underground. Sometimes, during winter
months, they develop from moist fogs and drizzles chilled to or beyond
the freezing point by cold air currents in the soil, and may be moved
about by such currents. Ice fogs are composed of minute particles; snow
particles are much larger and more visible but both may be seen
occasionally by exploring with a flashlight at night. Eventually they are
melted by warmer air currents, or by contact with deeper warmer layers
of soil, and provide moisture for plants.
Underground moisture, from whatever source, is never "pure" water. It
always contains dissolved gases and minerals of various kinds: some
gathered by rainwater as it falls from the sky; some absorbed by
subsurface fogs, drizzles and snows. Rainwater, for example, gathers
dust particles and carbon dioxide gas. Plant roots suck in such moisture
and then the dissolved gases and minerals are changed into foods that
sustain plant and animal life.
Little climates, underground, are real and vital.
To return to the Nature Bulletins Click Here!
Update: June 2012