Geophysical Characterization of Geologic Features in the Area of the Valdina Farms Sinkhole, Texas Bruce Smith 1, Jeff Paine 2,David Smith 1,Steve Johnson 3, John Waugh 4, Jared Abraham 1, Charles Blome 1, and Geary Schindel

Valdina Farms Sinkhole Edwards Aquifer Location

KARST 101 Should not be needed for a karst session so take a look at some pictures

Sinkhole entrance

Sinkhole map Sinkhole feature is about 850 meters long…say 5m average square area then have 4,450 cubic meter volume

Interior pictures

Recharge 2002 recharge event 14,450 acre feet of water into sinkhole 1 acre foot of water = 1,233 cubic meters so recharge was 17 million cubic meters of water Known volume of cave perhaps 5000 m 3 TWO ORDERS OF MAGNETUDE MORE WATER THAN CAVE VOLUME HYDROLOGY 101

GEOPHYSICS HEM Survey SENSOR SYSTEM  6 EM Frequencies 400 – 100,000 Hz  Internal Magnetometer  High Resolution GPS  Laser Altimeter

Preliminary geologic map from Kyle and Collins HEM SURVEY RECHARGE ZONE RECHARGE ZONE CATCHMENT AREA CATCHMENT AREA CONFINED ZONE NOT CONFINED ZONE Valdina Farms Sink hole and flight line

Line Vertical Exaggeration ~x m 1 Mile 100m100m Trinity Group SinkholeSinkhole Del Rio Clay Edwards Group nothing SOUTH NORTH Geophysical structure correlation Mapped structure correlation

Enlargement of Sinkhole area Depth metersDepth meters South North Arrows show EW intersection of sinkhole Valdina sinkhole entrance Sensor height

Surface resistivity interpretation Interpreted near surface Apparent Resistivity Allen Clark and Jason Faith

31 Meter Depth Slice Resistivity

97 Meter Depth Slice Resistivity

Resistivity 3D model area

3D Resistivity Model in Progress Seco Creek Woodard Cave Fault Trinity Capture area Recharge area Sinkhole

Conclusions New mapping from airborne geophysics shows that the sinkhole is located in a much more complex structural setting than previously thought Recharge flow paths are much more complex than previously thought (ramp structures and occluding faults) Apparent resistivity map indicates other features with similar electrical signatures that can be investigated as possible recharge points