The four thermal springs in the study area contain highly mineralized water with similar chemical compositions but varying hardness levels. Seismic activity in the area has increased since 2010, including a 5.0 magnitude earthquake in 2011. The study analyzed water samples from 2011-2013 to see if tremors affected water chemistry or temperature. Sodium and chloride concentrations in some springs increased after seismic events, while temperatures decreased. A correlation was found between higher river flows and increased seismic activity. More data is needed to fully understand links between earthquakes, spring water chemistry and the Orange River.

1. THERMAL SPRINGS IN THE LOWER ORANGE RIVER VALLEY
Danita Hohne1, Henno Gericke2
Department Water and Sanitation,
1Upington, Northern Cape, South Africa; email: HohneD@dws.gov.za
2Kimberley, Northern Cape, South Africa; email: GerickeH@dws.gov.za
Since June 2010 and still ongoing today, the Lower Orange River Valley has experienced over a 1168 tremors and earthquakes in the vicinity of Augrabies. Of these 1168 tremors, 71 quakes registered above 3 on the Richter scale and on 18
December 2011, the area was struck with an earthquake that registered 5 on the Richter scale. Four thermal springs are also located near this earthquake zone and the temperature of the water has a range of between 38°C -46.6°C, according to
Kent LE. (1949 /1969). 25°C is the division between thermal and non-thermal waters and the thermal gradient for the Riemvasmaak area is 24°C, clearly indicating that the four springs are thermal when looking at the temperature difference. The
Department of Water and Sanitation has been monitoring these springs monthly since 2011 and has been taking field measurements and chemical analyses.
The aim of this study is a) to see if the tremors and earthquakes have an effect on the chemistry of the thermal springs, b) to create a data set for the thermal springs, as these springs was recorded and mentioned in Kent LE. reports of 1949 and
1969 but no samples were collected and analysed, c) to see if the water source for the groundwater in the area and the thermal springs are connected and d) to see if the recent floods may have had an influence on the earthquake zone seeing as the
Orange River runs through the zone.
It should also be noted that during the time of the increased seismic activity in the Augrabies area, two floods occurred, one in 2010 and the other in 2011, this poster will also investigate the possibility that the increased flow of the river might have
had an impact on the seismic activity.
.
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Abstract and Introduction
Location of Study Area, Geology and Data
Capturing
Data Representation and Interpretation
Results
Conclusion
References
Akromah, L. ‘Earthquake relocation using the double difference method in the Augrabies Area.” Report; Council for
Geoscience; April 2013
Boeleman, R.; Bowels, M.; Cloete, D. and Coetzee FJ. “1:250 000 Metallogenic Series 2820 Upington.” Council for
Geoscience, 1997.
Geology of South Africa; Geological Socitity of South Africa; 2006
Kent, L.E. (1949) “The Thermal Waters of the Union of South Africa and South West Africa” Transactions of the
Geological Society of South Africa, 52, 231 – 264.
Moen, HFG. “1:250 000 Geological Series 2818 Onseepkans.” Council for Geoscience, 2007.
National Groundwater Archive (NGA)
Saunders, I. Ottemoller, L. Brandt, M.B.C. and Fourie. C.J.S. “ Calibration of an ML scale for South Africa using tectonic
earthquake data recorded by the South African Seismograph Network: 2006-2009.” Journal of Seismology;
August 2012
Oliver. J. and Jonker. N. “ Optimal utilasation of thermal springs in South Africa.” WRC Report TT 577/13
Van Niekerk, H; Silberbauer, MJ. And Maluleke, M. “Geographical differences in the relationship between total dissolved
solids and electrical conductivity in South African rivers.” Water SA Vol. 40 No. 1 January 2014
VonBackstorm; J.W. (1957) “The Riemvasmaak Thermal Spring, Gordonia District, Cape Province.” GH Report Nr. 1025
Water Monitoring System (WMS)
The data of four springs were presented, one classified as thermal and three as hot. Water from the springs is highly
mineralized chloride-sulphate brines. The springs show similar chemical composition, with variances in hardness and
sodium chloride content. The water from the springs is not fit for human consumption. The groundwater and thermal
spring analyses do show a correlation and therefore it can be assumed that the resources for the thermal water could
be groundwater.
At this stage no age determination was done on the water and it would be done in future not just to determine the age of
the water but it would also be a good test to do especially when another earthquake swarm takes place in the study
area. It could then determine if there is an increase or decrease in flow of the thermal water. From the data collected it
would also seem as if there is a correlation between the Orange River when in flood and the increase in seismic activity.
It would be suggested that this must be looked at in future when other floods occur to establish a definitive link between
the increased activities and floods.
A plausible correlation between seismic activity, water temperature and chemical composition, specifically sodium and
chloride concentrations, are proposed; however, it should be noted that the current seismic activities are not scaled
according to distances from the springs. The Council of Geoscience could also determine which of the faults in the
study area have been activated and these faults can be monitored and if possible loggers can be installed to see if any
of the river water is infiltrating the thermal spring system.
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Figure 1: The locations of the thermal springs are indicated by the starts in the map above.
Boreholes are shown as red dots, whilst river sampling points are given in blue. The
magnitudes of various seismic tremors are shown in greys.
GEOLOGY:
The study area is located in the Kakamas Terrane one of five major subdivisions of the
Namaqua-Natal Province. The age of the Kakamas Terrane is around ~2000Ma. The
eastern boundary of the Terrane is determined by the Boven Rugzeer Shear Zone and
in the west by the Hartbees River Thrust. The Kakamas Terrane stretches from
Onseepkans in the west to Keimoes in the east and around 200km south to Kenhardt
and Putsonderwater and north into Namibia. In the Kakamas Terrane the Neusberg
Shear Zone is trending NNW (Geology of South Africa, 2006).
Because of the geology the study area is highly deformed and there are numerous
faults and shear zones that can contribute to areas that might be weak in the crust
contributing to the seismic activities. The Orange River may also follow a weak zone
that contributes to the seismic activity. A concentration of the epicentres lie parallel to
the Orange River and this was found to be on both sides of the river. Structural maps
also show faults striking parallel to that all along the river. Because of the wide zone of
faults around the river, some of the faults are being activated by the strain in the crust
(Akromah, L. 2013).
Table 1: Thermal springs located in the study area and the geology
METHODS OF SAMPLING: WATER SAMPLES AND SEISMIC DATA :
Monthly groundwater samples were collected at the four thermal springs from February
2011. Samples from the two stations in the Orange River Upington (D7H005) and
Neusberg (D7H014) were also taken monthly.
The National Seismic Network of South Africa is run by the Council for Geoscience. To
collect seismic data there is about 29 stations around South Africa that register the
local magnitude, based on the Richter definition which is determined by local geology.
Three stations in the vicinity of the study area have recorded seismic data. The stations
are situated near Augrabies, Keimoes and Upington.
Since February 2010 there has been an increase in seismic activity in the study area.
The largest earthquake to date was on 25 January 2011 of 4.9 on the local magnitude
scale (Saunders, I. et al. 2012).
Since 1990 till present there have been more than 2500 tremors and earthquakes in
the study area, with most of the tremors occurring between 2010-2014.
The chemical compositions of the springs’ water were determined over a period
of time ranging from 2011 to 2013. The average value variations in quality over
time are indicated in the Piper diagrams in Figure 2. The pH values of the four
springs are all clustered around 8.3, with the exception of SF1, which is only
slightly lower. The springs are neither corrosive nor depositional – and are for
general purposes considered neutral. TDS values are high, ranging between
2200 and 3200 mg/l. The main ionic components are sodium, chloride and
sulphate ions; hence, using Bond et al.’s classification, all four springs can be
classified as highly mineralized chloride-sulphate waters.
The springs’ water is not suitable for consumption; specifically exceeding
recommended values for sodium, fluoride, sulphates and chlorides. Water quality
standards are given as specified by SANS241-2011.
Piper diagrams, given in Figure 2, were used to visualize the chemical
composition of the springs’ water. All four springs are sodium chloride brines.
Very low carbonate or hydrogen carbonate concentrations were observed. All
four springs have sulphate ion concentrations of above 500 mg/l. In terms of
cations Na+ is most prevalent. RP1 and RP3 are moderately hard, whilst SF1
and RVM1 can be considered hard in terms of Ca2+ concentrations.
The chemical compositions of the aforementioned springs were also compared
to that of the surrounding groundwater sources and two river monitoring stations
(Figure 4). Greater similarity between ground water sources (boreholes) and the
springs occur than with water from the Orange River. The springs show very
similar water compositions to each other, with SF1 and RVM1 being more
mineralized and having harder water. It should also be noted that only RP1 and
RP3 share the same quaternary drainage region (D81E) as indicated in Figure 1.
Figure 3 allows for the observation of the main chemical constituents that were
monitored over time. Variances in the temperature of the thermal springs as well
as the magnitudes of the tremors illustrated in Figure 1 are also plotted versus
time.
For RVM1 it is interesting to note that there is a spike in sodium chloride during
September 2011, this period was preceded with higher seismic activity. In August
2012 a large temperature drop was observed at RVM1, preceded by a slight
increase in Si, a drop in sodium chloride and a slight increase in sulphate
concentrations. Increased seismic activity preceded this change.
RP1 (Figure 3) shows variances in sodium, chloride and sulphate concentrations
after significant seismic activity. These variations are small. Decreased water
temperature was also observed following the periods of higher seismic activities.
A similar situation is observed for RP3 (Figure 3); however, the variations are
more pronounced. This pattern appears to hold for SF1 as well; where increased
seismic activity can lead to a spike in Na+ or Cl- or both, accompanied by a drop
in temperature.
Endothermic dissolution of particulates liberated by seismic activity may impact
the temperature of the springs; however, the increases in concentrations are not
substantial enough to justify the extent of the drops in temperature.
A comparison of tremor activity and Orange river flow rates (Figure 3) indicate a
possible link between the two.
Data Representation
Figure 2: Piper diagrams of the four springs. Dates for the values range from 2011
(lighter) to 2013 (darker).
Figure 3: Combined plot for RVM, RP1, RP3 and SF1 respectively. Top: Plot
showing how various ion concentrations vary with time. Temperature of the
spring’s water versus time. Flow rates of the Orange River at two monitoring
stations. Bottom: Seismic activity versus time.
Name Geology Estimated Depth
of circulation
Estimated
Temperature
Quaternary
Drainage
Region
Southern
Farms (SF1)
Naros Granite
and Warmbad
Suid Gneiss
1.124km 33.74°C D81D
Riemvasmaak
(RVM)
Naros Granite
and Warmbad
Suid Gneiss
1.517km 45.35°C D42E
Raap en
Skraap 1 (RP1)
Schuitdrift Gneiss
and it borders
with the Yas
Gneis
1.22km 37.28°C D81E
Raap en
Skraap 3 (RP3)
Riemvasmaak
Gneiss
1.242km 36.62°C D81E
The study area is located in the North-Western region of the Northern Cape next to the
border of Namibia. The locations of the four thermal springs are indicated in the Table
1. RP1 and RP3 are located about 60 m apart. The locations of the springs are
indicated in the map in Figure 1.
Figure 4: Piper diagram comparing the water chemistry of the springs
to that of surrounding groundwater sources and river monitoring data.
.
Conclusion