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Volcanic monitoring for radon and chemical species in the soil and in spring water samples
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Radiation Measurements 36 (2003) 379 – 383 www.elsevier.com/locate/radmeas
Volcanic monitoring for radon and chemical species in the soil and in spring water samples N. Segoviaa;∗ , M.A. Armientab , C. Valdesb , M. Menab , J.L. Seidelc , M. Monninc , P. Pe˜naa , M.B.E. Lopeza , A.V. Reyesa a Instituto
Nacional de Investigaciones Nucleares (ININ), Ap. Post 18-1027, Mexico D.F. 11801, Mexico b IGFUNAM, Ciudad Universitaria, 04510 Mexico D.F., Mexico c UMR 5569 CNRS Hydrosciences, Montpellier, France Received 21 October 2002; accepted 29 April 2003
Abstract Soil radon has been monitored at two 4xed stations in the northern 6ank of Popocatepetl Volcano, a high risk volcano located 60 km SE from Mexico City. Water samples from three springs were also studied for radon as well as major and trace elements. Radon in the soil was recorded using track detectors. Radon in the water samples was evaluated using the liquid scintillation method and an Alphaguard. The major elements were determined through conventional chemical methods and trace elements using an ICP-MS equipment. Soil radon levels were low, indicating a moderate di>use degassing through the 6anks of the volcano. Groundwater radon had almost no relation with the eruptive stages. Water chemistry was stable in the reported time (2000 –2002). c 2003 Elsevier Ltd. All rights reserved. Keywords: Active volcano; Soil and groundwater radon; SSNTD; Major and trace elements
1. Introduction Explosive eruptions and passively degassing volcanoes can release signi4cant quantities of gas through their 6anks as well as from crater fumaroles. Among them, radon and CO2 have shown useful results as indicators of gas 6ow of magmatic origin (De la Cruz Reyna et al., 1985; Connor et al., 1996; Heiligmann et al., 1997). Measurements of gases in soil gas and the chemical composition of groundwater from springs and wells at several volcanoes around the world have shown that spatial and temporal variations can provide an insight into the dynamics of active volcanoes and eventually to be used as a tool for the prediction of volcanic eruptions (Armienta and De la Cruz-Reyna, 1995; Varley and Armienta, 2001; Segovia et al., 2002). Since 1994, the Popocatepetl Volcano started an eruptive phase. Its geographical position, about 60 km SE from ∗ Corresponding author. Tel.: +52-55-56582025; fax: +52-5329-7332. E-mail address: [email protected] (N. Segovia).
Mexico City, Mexico, where the largest population concentration in the country is settled, and the evidence of large eruptions in historical times makes this volcano a high-risk one. The main purpose of the present paper is to analyse the e>ect of the recent activity on several parameters such as soil and groundwater radon and chemical composition of groundwater.
2. Experimental 2.1. The sites Popocatepetl Volcano (altitude 5465 m) is located in the central part of the Mexican Neo-Volcanic Belt (19◦ 03 36 N; 98◦ 31 18 W). In December 1994, an eruptive stage started and evolved with 6uctuating activity. The soil gas radon monitoring was performed at two 4xed stations located at 7.5 and 4:7 km from the crater at Paso de Cortes (altitude 3400 m) and Tlamacas (altitude 4000 m) on the northern 6ank of the volcano. These two stations
c 2003 Elsevier Ltd. All rights reserved. 1350-4487/03/$ - see front matter doi:10.1016/S1350-4487(03)00155-0
380
N. Segovia et al. / Radiation Measurements 36 (2003) 379 – 383
Fig. 1. Location of the soil monitoring sites at Paso de Cortes and Tlamacas and the three water springs: Axocopan, Atlimeyaya and Calvario.
are 5 km apart from each other and their soil characteristics are quite di>erent essentially due to the altitude factor. Paso de Cortes station corresponds to a conifer and oak forest with the top soil organic matter layer up to almost 70 cm, while Tlamacas is found at the upper cinder cone of the volcano above the tree line, with the top soil formed from non-consolidated volcanic ashes having no vegetation. Groundwater radon was measured in water samples obtained from three springs, Atlimeyaya, Axocopan and Calvario in the southern 6ank (Fig. 1). The spring waters are used mainly for domestic activities.
added was used for the determination of Na+ , K + , Ca2+ and Mg2+ . The sampling for trace elements dissolved in the water was performed with 60 ml polyethylene bottles previously washed and decontaminated. One day before the sampling, the bottles and covers were rinsed and 4lled with deionized water. In the 4eld two samples were taken at each place, one with the water sample and the other with deionized water used as a 4eld blank. The samples were 4ltered under a laminar 6ow hood and acidi4ed with ultrapure HNO3 (1% v/v).
2.2. Water sampling
2.3. Measurement techniques
Water sampling for radon determination was carried out in 125 ml polyethylene bottles perfectly sealed to avoid degassing. One litre polyethylene bottles were used for major chemical components sampling of chemical species such as Cl− , SO2− 4 , and SiO2 . A 500 ml sample with 3 ml HNO3
Long term soil radon determination (70 cm depth) was performed with solid state nuclear track detectors (SSNTD), LR-115 type II, from Dosirad Co., France. The details of the methodology have been previously reported (Segovia et al., 2002).
N. Segovia et al. / Radiation Measurements 36 (2003) 379 – 383
The water samples were analysed for dissolved radon with a Packard TRI-CARB 2700TR liquid scintillation detection system (Olguin et al., 1993). Several determinations in the water samples were cross-checked with an Alphaguard. In the 4eld, electrical conductivity was determined with a conductimeter (Conductronic PC18). Temperature and pH were determined with a Schott pH-Meter CG 837, calibrated before each measurement using a 4 pH bu>er solution. Chemical analyses were performed by standard methods, as given in APHA-AWWA-WPCF (1995). The accuracy of the analyses was checked by the ionic charge balance. Trace elements were determined using an ICP-MS (Inductively Coupled Mass Spectrometer) VG Plasma Quad 2 Turbo Plus at the University of Montpellier, France. Calibration was performed with 5 and 10 g L−1 solution containing all the elements to be analysed. A 10 g L−1 115 In and 209 Bi solution was used as internal standard in order to correct instrumental drift (Morton et al., 1998).
381
3. Results and discussion The Popocateptl seismic activity from 2000 to April 2002 is shown in Fig. 2. In this 4gure the long period (LP) events per day are related to the motion of volcanic 6uids. The volcano tectonic (VT) events are correlated to brittle fracture. During the period of study, the volcanic activity was relatively low, showing a volcanic explosivity index (VEI) lower than one (Newhall and Self, 1982). However, in the period December 2000 –January 2001, larger activity occurred and the population living around the volcano had to be evacuated. The soil radon 6uctuations observed at Paso de Cortes and Tlamacas with SSNTDs in the period are shown in Fig. 3. The average radon in soil values were quite low being slightly higher at Paso de Cortes as compared with Tlamacas. This behaviour is probably related to the gas di>usion in the soil, since Tlamacas soil is formed by non-consolidated volcanic ashes capable of promoting the gas di>usion from
0
200
-5
100
-10
0 2000
2001
LP events /day
VT events
Depth (km)
5
2002
Fig. 2. The volcanic activity 2000 –2002 at Popocatepetl volcano. The continuous graph represent long period (LP) volcanic events per day. Circles correspond to the depth of volcano tectonic (VT) events. Small explosions are indicated by “e” and large explosions by “E”.
6 TLAMACAS
PASO DE CORTES
5
kBq m-3
4 3 2 1 0 J F M A M J
J A S O N D J F M A M J
2000
J A S O N D J F M A M J
2001
J
2002
Date Fig. 3. Soil radon concentration (kBq m−3 ) at Tlamacas and Paso de Cortes measured with track detectors during 2000 –2002.
382
N. Segovia et al. / Radiation Measurements 36 (2003) 379 – 383
4 ATLIMEYAYA
AXOCOPAN
EL CALVARIO
Bq L-1
3
2
1
0 F M A M J J A S O N D J F M A M J J A S O N D J F M A M J 2000
2001
2002
Date Fig. 4. Radon concentration (Bq L−1 ) in the water samples at Atlimeyaya, Axocopan and Calvario during 2000 –2002. Table 1 Examples of major species (mg L−1 ) and trace elements (g L−1 ) in spring water samples from Atlimeyaya, Axocopan and Calvario Sites
Ca2+ Mg2+ Na+ K + Cl− SO2− HCO− total alk. F− SiO2 T (◦ C) pH E.C. (S=cm) Bal. (%) 4 3
Date
Major species (mg L−1 ) Atlimeyaya 08/02/01 11.4 13/06/02 10.7 Axocopan 08/02/01 37.0 13/06/02 35.7 Calvario 08/02/01 10.4 13/06/02 9.9 Sites
Date
Li L−1 )
Trace elements (g Atlimeyaya 15/06/00 04/04/01 Axocopan 15/06/00 04/04/01 Calvario 15/06/00 04/04/01
18.39 18.66 74.99 73.47 15.63 16.06
9.3 7.5 41.3 42.6 9.6 8.2
13.2 15.3 46.0 56.2 12.7 12.4
2.8 2.5 6.5 6.3 2.4 2.1
6.5 2.6 18.0 17.6 7.0 3.5
7.1 6.5 38.3 40.8 23.7 21.1
100.6 99.1 407.5 403.8 69.2 69.4
As
0.6 0.5 0.5 0.5 0.4 0.4 Rb
54.6 60.6 82.7 91.4 60.7 66.3 Sr
14.0 14.0 20.0 20.0 17.0 16.0 Mo
6.6 6.5 6.0 6.0 6.7 6.5
B
Cr
Mn
Co
Cu
124.62 127.84 249.05 279.81 26.73 27.95
1.95 1.69 3.85 8.25 — —
0.10 0.22 0.69 0.73 0.03 0.11
0.05 0.05 0.09 0.09 0.03 0.04
0.72 14.53 1.32 8.38 66.79 1.72 0.07 1.59 4.86 1.15 8.03 65.29 1.62 0.06 0.30 2.79 1.30 15.75 241.26 3.57 0.06 2.73 5.1 1.36 16.16 248.63 3.58 0.05 0.68 7.34 3.12 6.75 39.23 0.96 0.04 1.81 — 3.31 6.85 39.17 0.90 0.02
the top soil to the atmosphere. In 2000, a rise in soil radon is particularly observed at Paso de Cortes in the middle of the year, probably due to the rain season. Paso de Cortes station is located in the forest and the soil humidity in6uences the shallow radon content. Additionally soil radon increases in October, at the beginning of the seismicity changes that culminate with the December 2000 –January 2001 activity. Tlamacas, the closest station to the cone, shows a gradual increase in soil radon that also reaches a maximum with the occurrence of the December 2000 activity. In 2001, Paso de Cortes station had an increase in soil radon that stayed 1 month after the highest eruptive activity of January 22. A soil radon peak in the middle of the year coincides both with the rain season and with the starting point of small
Zn
82.5 81.2 334.0 331.0 56.7 56.9
Cd
142.0 142.0 603.0 602.0 151.0 145.0 Cs
0.04 1.3 −3:6 −0:3 2.8 2.8 Ba
Pb
U
0.40 6.47 0.14 0.23 0.39 6.09 0.14 0.21 0.43 23.34 2.98 1.12 0.44 24.30 0.29 1.15 0.37 4.67 0.30 0.07 0.37 4.59 0.30 0.08
dome formation in the crater. However, at Tlamacas a great stability is observed in 2001. In 2002, both stations showed an increase. The present eruptive stage was of relatively low volcanic activity and low soil radon levels. Varley and Armienta (2001), report that Popocatepetl have generally low soil radon and CO2 probably due to the absence of signi4cant migration of magmatic gas to the surface on the 6anks of the volcano. Groundwater radon concentration values at the springs around the volcano are shown in Fig. 4. The radon levels were quite low and showed an increase from April to June 2000, at Atlimeyaya and Axocopan, decreasing in July and reaching the maximum in the monitoring period for the three springs in August 2000. After August 2000, when the
N. Segovia et al. / Radiation Measurements 36 (2003) 379 – 383
volcano initiated the changes going to the eruptive activity of December 2000, a sudden decrease occurred in groundwater radon that continued with small 6uctuations until June 2002. This behaviour probably resulted from internal fracture changes in the volcano due to the increased seismicity initiated in September 2000. We assume that those changes induced a poor interaction between the volcanic gas transported through these fractures and the sampled aquifers. Some degree of stability was observed along the time for chemical species and trace elements at Axocopan, Calvario and Atlimeyaya springs. An example of the values obtained is shown in Table 1. The chemical species had higher concentration values at Axocopan indicating larger mineralization characteristics at this spring. In the Table, the values obtained from samplings performed in consecutive years were similar, indicating a quite low e>ect of the eruptive pattern of the volcano in the water chemistry. It is worth mentioning that radon, being a gas, has a larger probability to be transported in comparison with dissolved chemical compounds in groundwater. Meanwhile, radon 6uctuations are expected to be more sensitive to small internal volcanic changes than water chemistry. Each one of the three springs showed its own chemical identity and no striking changes in the time were observed. For the studied eruptive period, the soil radon levels were low indicating a quite moderate di>use degassing through the 6anks of the volcano. Soil radon 6uctuations showed a small e>ect with volcanic activity. Groundwater radon had almost no relation with the eruptive stages. The water chemistry of nearby springs was stable in the time, even if the water characteristics showed di>erences in the water origin for each spring. The present results agree with the low volcanic activity from the Popocatepetl in the period of study. Acknowledgements The authors acknowledge D. Cruz, S. Ceballos, F. Montes, N. Ceniceros, A. Aguayo and O. Cruz for
383
technical assistance. We also acknowledge partial 4nancial support from CONACyT. References APHA-AWWA-WPCF, 1995. Standard Methods for the Examination of Water and Wastewater. 19th Edition, American Public Health Association (APHA) American Water Works Association (AWWA), Water Pollution Control Federation (WPCF), Washington DC. Armienta, M.A., De la Cruz-Reyna, S., 1995. Some hydro-geochemical 6uctuations observed in Mexico related to volcanic activity. Appl. Geochem. 10, 215–227. Connor, Ch., Brittain, H., LaFemina, P., Navarro, M., Conway, M., 1996. Soil 222 Rn pulse during the initial phase of the June– August 1995 eruption of Cerro Negro, Nicaragua. J. Volcanol. Geotherm. Res. 73, 119–127. De la Cruz Reyna, S., Mena, M., Segovia, N., Chalot, J.F., Seidel, J.L., Monnin, M., 1985. Radon emanometry in soil gases and activity in ashes from El Chichon volcano. Pure Appl. Geophys. 123, 407–421. Heiligmann, M., Stix, J., Williams, G., Sherwood, B., Garzon, G., 1997. Distal degassing of radon and carbon dioxide on Galeras Volcano, Columbia. J. Volcanol. Geotherm Res. 77, 267–283. Morton, O., Lounejeva, E., Hernandez, E., Seidel, J.L., Segovia, N., 1998. EvaluaciQon de la calidad de blancos: determinaciQon de elementos traza en agua deionizada y/o destilada. Actas Inst. Nal. Geoquim. 4, 107–112. Newhall, C.G., Self, F., 1982. The volcanic explosivity index (VEI): an estimate of explosive magnitude for historical volcanism. J. Geophys. Res. 87, 1231–1238. Olguin, M.T., Segovia, N., Tamez, E., Alcantara, M., Bulbulian, S., 1993. Radon concentration levels in groundwater from the City of Toluca, Mexico. Sci. Total Environ. 130, 43–50. Segovia, N., Armienta, M.A., Seidel, J.L., Monnin, M., Pe˜na, P., Lopez, M.B.E., Mena, M., Valdes, C., Tamez, E., Lopez, R.N., Aranda, P., 2002. Radon in soil and chemical composition of spring water near Popocatepetl volcano, Mexico. Geof. Int. 41, 399–405. Varley, N.R., Armienta, M.A., 2001. The absence of di>use degassing at Popocatepetl volcano, Mexico. Chem. Geol. 177, 157–173.
Radiation Measurements 36 (2003) 379 – 383 www.elsevier.com/locate/radmeas
Volcanic monitoring for radon and chemical species in the soil and in spring water samples N. Segoviaa;∗ , M.A. Armientab , C. Valdesb , M. Menab , J.L. Seidelc , M. Monninc , P. Pe˜naa , M.B.E. Lopeza , A.V. Reyesa a Instituto
Nacional de Investigaciones Nucleares (ININ), Ap. Post 18-1027, Mexico D.F. 11801, Mexico b IGFUNAM, Ciudad Universitaria, 04510 Mexico D.F., Mexico c UMR 5569 CNRS Hydrosciences, Montpellier, France Received 21 October 2002; accepted 29 April 2003
Abstract Soil radon has been monitored at two 4xed stations in the northern 6ank of Popocatepetl Volcano, a high risk volcano located 60 km SE from Mexico City. Water samples from three springs were also studied for radon as well as major and trace elements. Radon in the soil was recorded using track detectors. Radon in the water samples was evaluated using the liquid scintillation method and an Alphaguard. The major elements were determined through conventional chemical methods and trace elements using an ICP-MS equipment. Soil radon levels were low, indicating a moderate di>use degassing through the 6anks of the volcano. Groundwater radon had almost no relation with the eruptive stages. Water chemistry was stable in the reported time (2000 –2002). c 2003 Elsevier Ltd. All rights reserved. Keywords: Active volcano; Soil and groundwater radon; SSNTD; Major and trace elements
1. Introduction Explosive eruptions and passively degassing volcanoes can release signi4cant quantities of gas through their 6anks as well as from crater fumaroles. Among them, radon and CO2 have shown useful results as indicators of gas 6ow of magmatic origin (De la Cruz Reyna et al., 1985; Connor et al., 1996; Heiligmann et al., 1997). Measurements of gases in soil gas and the chemical composition of groundwater from springs and wells at several volcanoes around the world have shown that spatial and temporal variations can provide an insight into the dynamics of active volcanoes and eventually to be used as a tool for the prediction of volcanic eruptions (Armienta and De la Cruz-Reyna, 1995; Varley and Armienta, 2001; Segovia et al., 2002). Since 1994, the Popocatepetl Volcano started an eruptive phase. Its geographical position, about 60 km SE from ∗ Corresponding author. Tel.: +52-55-56582025; fax: +52-5329-7332. E-mail address: [email protected] (N. Segovia).
Mexico City, Mexico, where the largest population concentration in the country is settled, and the evidence of large eruptions in historical times makes this volcano a high-risk one. The main purpose of the present paper is to analyse the e>ect of the recent activity on several parameters such as soil and groundwater radon and chemical composition of groundwater.
2. Experimental 2.1. The sites Popocatepetl Volcano (altitude 5465 m) is located in the central part of the Mexican Neo-Volcanic Belt (19◦ 03 36 N; 98◦ 31 18 W). In December 1994, an eruptive stage started and evolved with 6uctuating activity. The soil gas radon monitoring was performed at two 4xed stations located at 7.5 and 4:7 km from the crater at Paso de Cortes (altitude 3400 m) and Tlamacas (altitude 4000 m) on the northern 6ank of the volcano. These two stations
c 2003 Elsevier Ltd. All rights reserved. 1350-4487/03/$ - see front matter doi:10.1016/S1350-4487(03)00155-0
380
N. Segovia et al. / Radiation Measurements 36 (2003) 379 – 383
Fig. 1. Location of the soil monitoring sites at Paso de Cortes and Tlamacas and the three water springs: Axocopan, Atlimeyaya and Calvario.
are 5 km apart from each other and their soil characteristics are quite di>erent essentially due to the altitude factor. Paso de Cortes station corresponds to a conifer and oak forest with the top soil organic matter layer up to almost 70 cm, while Tlamacas is found at the upper cinder cone of the volcano above the tree line, with the top soil formed from non-consolidated volcanic ashes having no vegetation. Groundwater radon was measured in water samples obtained from three springs, Atlimeyaya, Axocopan and Calvario in the southern 6ank (Fig. 1). The spring waters are used mainly for domestic activities.
added was used for the determination of Na+ , K + , Ca2+ and Mg2+ . The sampling for trace elements dissolved in the water was performed with 60 ml polyethylene bottles previously washed and decontaminated. One day before the sampling, the bottles and covers were rinsed and 4lled with deionized water. In the 4eld two samples were taken at each place, one with the water sample and the other with deionized water used as a 4eld blank. The samples were 4ltered under a laminar 6ow hood and acidi4ed with ultrapure HNO3 (1% v/v).
2.2. Water sampling
2.3. Measurement techniques
Water sampling for radon determination was carried out in 125 ml polyethylene bottles perfectly sealed to avoid degassing. One litre polyethylene bottles were used for major chemical components sampling of chemical species such as Cl− , SO2− 4 , and SiO2 . A 500 ml sample with 3 ml HNO3
Long term soil radon determination (70 cm depth) was performed with solid state nuclear track detectors (SSNTD), LR-115 type II, from Dosirad Co., France. The details of the methodology have been previously reported (Segovia et al., 2002).
N. Segovia et al. / Radiation Measurements 36 (2003) 379 – 383
The water samples were analysed for dissolved radon with a Packard TRI-CARB 2700TR liquid scintillation detection system (Olguin et al., 1993). Several determinations in the water samples were cross-checked with an Alphaguard. In the 4eld, electrical conductivity was determined with a conductimeter (Conductronic PC18). Temperature and pH were determined with a Schott pH-Meter CG 837, calibrated before each measurement using a 4 pH bu>er solution. Chemical analyses were performed by standard methods, as given in APHA-AWWA-WPCF (1995). The accuracy of the analyses was checked by the ionic charge balance. Trace elements were determined using an ICP-MS (Inductively Coupled Mass Spectrometer) VG Plasma Quad 2 Turbo Plus at the University of Montpellier, France. Calibration was performed with 5 and 10 g L−1 solution containing all the elements to be analysed. A 10 g L−1 115 In and 209 Bi solution was used as internal standard in order to correct instrumental drift (Morton et al., 1998).
381
3. Results and discussion The Popocateptl seismic activity from 2000 to April 2002 is shown in Fig. 2. In this 4gure the long period (LP) events per day are related to the motion of volcanic 6uids. The volcano tectonic (VT) events are correlated to brittle fracture. During the period of study, the volcanic activity was relatively low, showing a volcanic explosivity index (VEI) lower than one (Newhall and Self, 1982). However, in the period December 2000 –January 2001, larger activity occurred and the population living around the volcano had to be evacuated. The soil radon 6uctuations observed at Paso de Cortes and Tlamacas with SSNTDs in the period are shown in Fig. 3. The average radon in soil values were quite low being slightly higher at Paso de Cortes as compared with Tlamacas. This behaviour is probably related to the gas di>usion in the soil, since Tlamacas soil is formed by non-consolidated volcanic ashes capable of promoting the gas di>usion from
0
200
-5
100
-10
0 2000
2001
LP events /day
VT events
Depth (km)
5
2002
Fig. 2. The volcanic activity 2000 –2002 at Popocatepetl volcano. The continuous graph represent long period (LP) volcanic events per day. Circles correspond to the depth of volcano tectonic (VT) events. Small explosions are indicated by “e” and large explosions by “E”.
6 TLAMACAS
PASO DE CORTES
5
kBq m-3
4 3 2 1 0 J F M A M J
J A S O N D J F M A M J
2000
J A S O N D J F M A M J
2001
J
2002
Date Fig. 3. Soil radon concentration (kBq m−3 ) at Tlamacas and Paso de Cortes measured with track detectors during 2000 –2002.
382
N. Segovia et al. / Radiation Measurements 36 (2003) 379 – 383
4 ATLIMEYAYA
AXOCOPAN
EL CALVARIO
Bq L-1
3
2
1
0 F M A M J J A S O N D J F M A M J J A S O N D J F M A M J 2000
2001
2002
Date Fig. 4. Radon concentration (Bq L−1 ) in the water samples at Atlimeyaya, Axocopan and Calvario during 2000 –2002. Table 1 Examples of major species (mg L−1 ) and trace elements (g L−1 ) in spring water samples from Atlimeyaya, Axocopan and Calvario Sites
Ca2+ Mg2+ Na+ K + Cl− SO2− HCO− total alk. F− SiO2 T (◦ C) pH E.C. (S=cm) Bal. (%) 4 3
Date
Major species (mg L−1 ) Atlimeyaya 08/02/01 11.4 13/06/02 10.7 Axocopan 08/02/01 37.0 13/06/02 35.7 Calvario 08/02/01 10.4 13/06/02 9.9 Sites
Date
Li L−1 )
Trace elements (g Atlimeyaya 15/06/00 04/04/01 Axocopan 15/06/00 04/04/01 Calvario 15/06/00 04/04/01
18.39 18.66 74.99 73.47 15.63 16.06
9.3 7.5 41.3 42.6 9.6 8.2
13.2 15.3 46.0 56.2 12.7 12.4
2.8 2.5 6.5 6.3 2.4 2.1
6.5 2.6 18.0 17.6 7.0 3.5
7.1 6.5 38.3 40.8 23.7 21.1
100.6 99.1 407.5 403.8 69.2 69.4
As
0.6 0.5 0.5 0.5 0.4 0.4 Rb
54.6 60.6 82.7 91.4 60.7 66.3 Sr
14.0 14.0 20.0 20.0 17.0 16.0 Mo
6.6 6.5 6.0 6.0 6.7 6.5
B
Cr
Mn
Co
Cu
124.62 127.84 249.05 279.81 26.73 27.95
1.95 1.69 3.85 8.25 — —
0.10 0.22 0.69 0.73 0.03 0.11
0.05 0.05 0.09 0.09 0.03 0.04
0.72 14.53 1.32 8.38 66.79 1.72 0.07 1.59 4.86 1.15 8.03 65.29 1.62 0.06 0.30 2.79 1.30 15.75 241.26 3.57 0.06 2.73 5.1 1.36 16.16 248.63 3.58 0.05 0.68 7.34 3.12 6.75 39.23 0.96 0.04 1.81 — 3.31 6.85 39.17 0.90 0.02
the top soil to the atmosphere. In 2000, a rise in soil radon is particularly observed at Paso de Cortes in the middle of the year, probably due to the rain season. Paso de Cortes station is located in the forest and the soil humidity in6uences the shallow radon content. Additionally soil radon increases in October, at the beginning of the seismicity changes that culminate with the December 2000 –January 2001 activity. Tlamacas, the closest station to the cone, shows a gradual increase in soil radon that also reaches a maximum with the occurrence of the December 2000 activity. In 2001, Paso de Cortes station had an increase in soil radon that stayed 1 month after the highest eruptive activity of January 22. A soil radon peak in the middle of the year coincides both with the rain season and with the starting point of small
Zn
82.5 81.2 334.0 331.0 56.7 56.9
Cd
142.0 142.0 603.0 602.0 151.0 145.0 Cs
0.04 1.3 −3:6 −0:3 2.8 2.8 Ba
Pb
U
0.40 6.47 0.14 0.23 0.39 6.09 0.14 0.21 0.43 23.34 2.98 1.12 0.44 24.30 0.29 1.15 0.37 4.67 0.30 0.07 0.37 4.59 0.30 0.08
dome formation in the crater. However, at Tlamacas a great stability is observed in 2001. In 2002, both stations showed an increase. The present eruptive stage was of relatively low volcanic activity and low soil radon levels. Varley and Armienta (2001), report that Popocatepetl have generally low soil radon and CO2 probably due to the absence of signi4cant migration of magmatic gas to the surface on the 6anks of the volcano. Groundwater radon concentration values at the springs around the volcano are shown in Fig. 4. The radon levels were quite low and showed an increase from April to June 2000, at Atlimeyaya and Axocopan, decreasing in July and reaching the maximum in the monitoring period for the three springs in August 2000. After August 2000, when the
N. Segovia et al. / Radiation Measurements 36 (2003) 379 – 383
volcano initiated the changes going to the eruptive activity of December 2000, a sudden decrease occurred in groundwater radon that continued with small 6uctuations until June 2002. This behaviour probably resulted from internal fracture changes in the volcano due to the increased seismicity initiated in September 2000. We assume that those changes induced a poor interaction between the volcanic gas transported through these fractures and the sampled aquifers. Some degree of stability was observed along the time for chemical species and trace elements at Axocopan, Calvario and Atlimeyaya springs. An example of the values obtained is shown in Table 1. The chemical species had higher concentration values at Axocopan indicating larger mineralization characteristics at this spring. In the Table, the values obtained from samplings performed in consecutive years were similar, indicating a quite low e>ect of the eruptive pattern of the volcano in the water chemistry. It is worth mentioning that radon, being a gas, has a larger probability to be transported in comparison with dissolved chemical compounds in groundwater. Meanwhile, radon 6uctuations are expected to be more sensitive to small internal volcanic changes than water chemistry. Each one of the three springs showed its own chemical identity and no striking changes in the time were observed. For the studied eruptive period, the soil radon levels were low indicating a quite moderate di>use degassing through the 6anks of the volcano. Soil radon 6uctuations showed a small e>ect with volcanic activity. Groundwater radon had almost no relation with the eruptive stages. The water chemistry of nearby springs was stable in the time, even if the water characteristics showed di>erences in the water origin for each spring. The present results agree with the low volcanic activity from the Popocatepetl in the period of study. Acknowledgements The authors acknowledge D. Cruz, S. Ceballos, F. Montes, N. Ceniceros, A. Aguayo and O. Cruz for
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technical assistance. We also acknowledge partial 4nancial support from CONACyT. References APHA-AWWA-WPCF, 1995. Standard Methods for the Examination of Water and Wastewater. 19th Edition, American Public Health Association (APHA) American Water Works Association (AWWA), Water Pollution Control Federation (WPCF), Washington DC. Armienta, M.A., De la Cruz-Reyna, S., 1995. Some hydro-geochemical 6uctuations observed in Mexico related to volcanic activity. Appl. Geochem. 10, 215–227. Connor, Ch., Brittain, H., LaFemina, P., Navarro, M., Conway, M., 1996. Soil 222 Rn pulse during the initial phase of the June– August 1995 eruption of Cerro Negro, Nicaragua. J. Volcanol. Geotherm. Res. 73, 119–127. De la Cruz Reyna, S., Mena, M., Segovia, N., Chalot, J.F., Seidel, J.L., Monnin, M., 1985. Radon emanometry in soil gases and activity in ashes from El Chichon volcano. Pure Appl. Geophys. 123, 407–421. Heiligmann, M., Stix, J., Williams, G., Sherwood, B., Garzon, G., 1997. Distal degassing of radon and carbon dioxide on Galeras Volcano, Columbia. J. Volcanol. Geotherm Res. 77, 267–283. Morton, O., Lounejeva, E., Hernandez, E., Seidel, J.L., Segovia, N., 1998. EvaluaciQon de la calidad de blancos: determinaciQon de elementos traza en agua deionizada y/o destilada. Actas Inst. Nal. Geoquim. 4, 107–112. Newhall, C.G., Self, F., 1982. The volcanic explosivity index (VEI): an estimate of explosive magnitude for historical volcanism. J. Geophys. Res. 87, 1231–1238. Olguin, M.T., Segovia, N., Tamez, E., Alcantara, M., Bulbulian, S., 1993. Radon concentration levels in groundwater from the City of Toluca, Mexico. Sci. Total Environ. 130, 43–50. Segovia, N., Armienta, M.A., Seidel, J.L., Monnin, M., Pe˜na, P., Lopez, M.B.E., Mena, M., Valdes, C., Tamez, E., Lopez, R.N., Aranda, P., 2002. Radon in soil and chemical composition of spring water near Popocatepetl volcano, Mexico. Geof. Int. 41, 399–405. Varley, N.R., Armienta, M.A., 2001. The absence of di>use degassing at Popocatepetl volcano, Mexico. Chem. Geol. 177, 157–173.