Understanding the geology behind a landslide
Reported by: Steve Linscomb
Email: stevelinsc...@woaitv.com
Last Update: 6:42 pm
Landslide Close-Up (WOAI.com)
SAN ANTONIO - A number of Northwest Side homeowners are watching as
their homes are devastated as they slide down a slope. Sadly, there's
not much they can do. But many in the area -- and all across San
Antonio -- are wondering, why is it this happening?
Geologists say landslides and other types of land movments can, and
do, happen in South Central Texas for a number of different reasons.
Many times they happen in areas where construction is going on.
We talked with homeowners that could only watch their homes slide and
wonder what's happening. Travis Walston first noticed the crack in his
yard and called about it when it began to grow big enough to look down
into it.
"You could see the different layers... there's a lot of earth. There's
a lot of mother nature in this," Walston told News 4 WOAI. "I don't
understand the retaining wall. There's no rebar. There's really no
support."
So what could be happening here? We talked with Saint Mary's
University professor of geophysics Evelynn Mitchell who says it looks
to be an example of what is called "mass wasting." That's the downward
movement of earth and rock. At work are two forces.
"Your resistant forces are going to keep this slope held up over time.
The driving forces are what is encouraging the slope to move
downward," explained Professor Mitchell.
If the driving force downward is greater, you can have a collapse.
Mitchell says water collection can add more problems, expanding the
soil.
"Then the water is going to end up pushing along the slope, adding
more force and overcoming that resistant force," said Mitchell.
It could be a while before we know exactly what happened in that
Northwest Side neighborhood, but one thing's for sure; the landscape
across South Central Texas is changing... whether it be from manmade
or natural reasons.
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