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Journal of Volcanology and Geothermal Research 324 (2016) 156–168
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Journal of Volcanology and Geothermal Research
journal homepage: www.elsevier.com/locate/jvolgeores
Evidence of recent deep magmatic activity at Cerro Bravo-Cerro Machín
volcanic complex, central Colombia. Implications for future volcanic
activity at Nevado del Ruiz, Cerro Machín and other volcanoes
John Makario Londono
Colombia Geological Survey (CGS), Servicio Geológico Colombiano (SGC), Avenida 12 de Octubre 15-47, Manizales, Colombia
a r t i c l e
i n f o
Article history:
Received 29 October 2015
Received in revised form 2 June 2016
Accepted 8 June 2016
Available online 10 June 2016
Keywords:
Magmatic activity
Nevado del Ruiz volcano
Machin volcano
Magma intrusion
Volcanic activity
a b s t r a c t
In the last nine years (2007–2015), the Cerro Bravo-Cerro Machín volcanic complex (CBCMVC), located in central
Colombia, has experienced many changes in volcanic activity. In particular at Nevado del Ruiz volcano (NRV),
Cerro Machin volcano (CMV) and Cerro Bravo (CBV) volcano. The recent activity of NRV, as well as increasing
seismic activity at other volcanic centers of the CBCMVC, were preceded by notable changes in various geophysical and geochemical parameters, that suggests renewed magmatic activity is occurring at the volcanic complex.
The onset of this activity started with seismicity located west of the volcanic complex, followed by seismicity at
CBV and CMV. Later in 2010, strong seismicity was observed at NRV, with two small eruptions in 2012. After that,
seismicity has been observed intermittently at other volcanic centers such as Santa Isabel, Cerro España,
Paramillo de Santa Rosa, Quindío and Tolima volcanoes, which persists until today.
Local deformation was observed from 2007 at NRV, followed by possible regional deformation at various volcanic
centers between 2011 and 2013. In 2008, an increase in CO2 and Radon in soil was observed at CBV, followed by a
change in helium isotopes at CMV between 2009 and 2011. Moreover, SO2 showed an increase from 2010 at NRV,
with values remaining high until the present.
These observations suggest that renewed magmatic activity is currently occurring at CBCMVC. NRV shows
changes in its activity that may be related to this new magmatic activity. NRV is currently exhibiting the most
activity of any volcano in the CBCMVC, which may be due to it being the only open volcanic system at this
time. This suggests that over the coming years, there is a high probability of new unrest or an increase in volcanic
activity of other volcanoes of the CBCMVC.
© 2016 Elsevier B.V. All rights reserved.
1. Introduction
The study of ascending of magma from depth to the surface is one of
the most fascinating and intriguing issues in volcanology. Such magma
ascent can be studied from many different perspectives and with different focus. Geology and petrology can help to understand how magma
ascended in the past. During an eruptive episode it may be possible to
infer parameters for magma ascent if petrological and petrographic
data are available (Jaupart, 1998; Uto et al., 2001; Saito et al., 2010;
Takeuchi, 2011). Geophysics and geochemistry by means continuous
monitoring can help to detect changes in the magmatic system, and
possible onset of magma ascent (Bräuer et al., 2005; Chaussard and
Amelung, 2012, 2014; Thomas and Neuberg, 2014; Acocella et al.,
2015; Kazahaya et al., 2015; Christopher et al., 2015).
In this work, geophysical and geochemical data collected by
Colombia Geological Survey (CGS) from continuous monitoring of
E-mail address: [email protected]
http://dx.doi.org/10.1016/j.jvolgeores.2016.06.003
0377-0273/© 2016 Elsevier B.V. All rights reserved.
Cerro Bravo-Cerro Machin Volcanic Complex (CBCMVC) are analyzed
to infer magmatic activity. CBCMVC is located in central Colombia
(Fig. 1). Some of the most active and dangerous volcanoes in Colombia
belong to this complex (Méndez et al., 2002), such as Nevado del Ruiz
volcano (NRV), Cerro Bravo volcano (CBV) and Cerro Machín volcano
(CMV). The eruptive products of the CBCMVC are andesitic to dacitic
with only a smaller proportion of rocks of different composition. During
the last 2 Ma, these volcanic complexes have shown a variety of eruptive
styles. In the last 0.5 Ma NRV has exhibited vulcanian explosive activity
(Thouret et al., 1985; Thouret and Gourgaud, 1990), while CMV has produced six Plinian eruptions over the last 5000 years (Rueda, 2004). The
most recent period of eruptive activity started with the 1985 eruption of
NRV (VEI = 3). This eruption generated a lahar that killed more than
23,000 people. Since 1985 onward volcanoes such as NRV and CMV
have shown multiple signs of unrest.
Other volcanoes belonging to the CBCMVC can be considered active
volcanoes, for example, Santa Rosa volcano (SRV), Santa Isabel volcano
(SIV), Cerro España volcano (CEV), Nevado del Quindío volcano (NQV),
and Nevado del Tolima volcano (NTV) (Fig. 1). Although few studies
J.M. Londono / Journal of Volcanology and Geothermal Research 324 (2016) 156–168
157
Fig. 1. Location of Cerro Bravo-Cerro Machín Volcanic Complex (CBCMVC) and monitoring networks in operation during the two study periods. 1: Romeral volc (RV), 2:Cerro Bravo volc.
(CBV), 3: Nevado del Ruiz volc. (NRV), 4: St. Isabel volc. (SIV), 5:St. Rosa volc. (SRV), 6: Cerro Espana volc. (CEV), 7: Nevado del Quindío volc. (NQV), 8: Nevado del Tolima volc. (NTV), and
9: Cerrro Machín volc. (CMV).
have been done on these volcanoes, the Colombia Geological Survey
(CGS) has recently initiated research on these volcanoes.
Volcano monitoring of active volcanoes in Colombia started formally
in 1986. NRV, CMV, and NTV were the first volcanoes to be monitored in
Colombia. Since then, baselines of various monitoring parameters have
been established by CGS, such as seismicity, geochemistry and deformation. These long-running baselines are key to detecting temporal
changes in volcanic activity. With the increasing availability of
sophisticated instruments and techniques over the last few decades, it
is possible to detect or infer new magma input in volcanic complexes
(Lough et al., 2013). Sophisticated monitoring networks have been in
place since 2000, and several temporally complete datasets are available
for volcanoes in the CBCMVC. Analysis of changes in the baseline of
multiple monitoring parameters, such as seismicity, deformation and
geochemistry, suggests a possible change in volcanic activity in the
CBCMVC. In this work I propose that the geophysical and geochemical
data collected over the last 15 years (2000–2015) highlight the onset
of renewed magmatic activity at CBCMVC.
2. Sources of information and data
Various sources of data were used for the assessment of the ongoing
volcanic activity in the CBCMVC: a) Published tiltmeter results from CGS
(2007–2015); b) GPS data by Ordoñez et al. (2015); c) InSAR by
Lundgren et al. (2015a, 2015b); d) Geochemistry data by Inguaggiato
et al. (2014) and CGS (SGC, 2000 to 2015); e) Seismic data from NRV
and CMV (SGC, 2014, Londoño and Dionicio, 2011; Londoño and
Castaño, 2014); and finally, f) the seismic database of the Colombia Geological Survey (CGS). Some of the SO2 data used in this study were produced from the Giovanni online data system, which is developed and
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J.M. Londono / Journal of Volcanology and Geothermal Research 324 (2016) 156–168
maintained by NASA (http://giovanni.gsfc.nasa.gov/giovanni/). Seismicity, radon gas, CO2 gas, pH, SO4/Cl and tiltmeter data were reprocessed,
analyzed and integrated.
Time series before 2000 are not temporally complete for the entire
volcanic complex. For NRV and CMV continuous seismic data are available since 1986 and 1989, respectively. For NRV, CMV, NTV, and CBV
volcanoes, only sporadic geochemistry and hydrochemistry samples
and dry tilt measurements are available. With these time series I observed no important changes before 2000 for almost all volcanoes, except for NRV. Therefore, the studied time period will be focused from
2000 to 2015.
Fig. 1 shows the location of CBCMVC, the main volcanoes of the complex, and the networks used for volcano monitoring. The basic configuration of the monitoring networks has not changed significantly
between 2000 and 2015. At some seismic stations the sensor has been
upgraded from short-period to broad-band instruments, and the
number of near-field stations has been increased at NRV and CMV to
improve coverage and improve earthquake locations at these volcanoes.
To create continuous and internally consistent baselines, the same
stations have been used for data analysis and statistics throughout the
period 2000 to 2015.
Electronic tiltmeters have been used intermittently since 2000, and
since 2000 dry tiltmeters, precision leveling vectors and EDM have
been used at several volcanoes, however, measurements were not continuous during this time. A complete set of electronic tiltmeter data is
available after 2007 for NRV, CMV and NTV volcanoes. GPS instruments
have been deployed by CGS since 2010 at CMV, and since 2011 at NRV
(SGC, 2014); therefore, GPS data is not complete, however, the trend
is the same as that showed by the electronic tiltmeter network (SGC,
2015a, 2015b).
Geochemistry data is available since the early 1990s mainly for NRV.
Periodic measurements of pH, Cl, SO4 and temperature at hot springs
are available for some volcanoes since 2008. Since 2004 until 2015,
satellite derived SO2 data has been available. From 2009 to 2015 DOAS
instruments were deployed at NRV. Radon gas and CO2 in soil has
been available from 2005 to 2009 for NRV, CMV and CBV. At CMV data
for CO2 in soil detection for N 400 points around the volcano are
available from two field campaigns in 2013 and 2014.
Due to the longevity and consistency of these seismic, deformation
and geochemical datasets, any temporal or spatial changes in these
baselines is likely due to changes in volcanic activity rather than changes due to instrumentation (Fig. 2). Some variables such as temperature
Fig. 2. Time evolution of monitoring networks and data from volcanic centers of the CBCMVC. Vertical bars represent number of stations and color represents the volcano.
J.M. Londono / Journal of Volcanology and Geothermal Research 324 (2016) 156–168
159
in hot springs, EDM, dry tiltmeters, or precision leveling vectors, were
not included in the analysis because either no changes were detected
during the study period (i.e. a constant value, or measurements within
instrument error), or data were not complete. Fig. 2 shows the timeline
of monitoring networks used for analysis.
3. Results
Fig. 3 shows temporal variation of the geophysical and geochemical
parameters analyzed at each volcano, and Table 1 summarizes the main
changes over time. In Fig. 3 data have been normalized with respect to
the maximum value (taken as unity) for each volcano during the period
2000–2015. This was done to display all the available data in a unique
simple plot, because about 40 individual time series were available.
First, the yearly average was calculated for each available time series
across all stations at each volcano throughout the study period. Then
the average was normalized with respect to the maximum value of
each dataset and plotted as a color bar. The color represents the volcano.
For the number of earthquakes, all small earthquakes with ML b 1.3
were removed from the catalog at all volcanoes. This was done to
eliminate the effect of varying sensitivity of the instruments, due to
occasional changes from short-period seismic stations to broad-band
seismic stations throughout the study period.
Fig. 3 and Table 1, show that several volcanic centers exhibited
changes after 2007, while the period 2000–2007 did not show any
significant changes in those parameters. As mentioned previously, the
basic monitoring networks have been well established since 2000
(Fig. 2). While there have been some improvements to monitoring networks, in particular seismic networks, since 2007, these changes alone
are not sufficient to explain the changes in observed geophysical and
geochemical monitoring data (Fig. 3). Not all volcanoes have the same
monitoring networks for each geophysical or geochemical variable,
and there may be some bias towards volcanoes with higher activity
being more closely monitored and hence having more complete data
(Fig. 2). Therefore this study focuses on those volcanoes with the most
complete data such as NRV, CMV, NTV and CBV. Based on the results
shown in Fig. 3, further analysis of the data was divided into two
periods; from 2000 to 2006, and from 2007 to 2015.
3.1. Seismicity
Before comparing spatial distribution of seismicity for the two chosen periods, the seismic catalog must be homogeneous. The entire catalog ranged from − 2.5 to 4.7 ML. The completeness magnitude (Mc)
trough time was calculated by using the Maximum curvature method,
taking a sampling window of 500 data points, with an overlap of 4
(Wiemer and Wyss, 2002). Fig. 4 shows the variation in time of completeness magnitude (Mc). Average Mc for the seismic catalog for all
studied period (2000–2015) was − 0.19, including all the available
earthquakes. This means that the seismic catalog is complete at very
low magnitudes almost all the time. To ensure comparison of a complete catalog for both study periods, and to remove any potential instrument detection effects (e.g. short-period vs. broad-band), mainly the
effect of very small earthquakes detected by broad-band stations, only
earthquakes with ML N 1.3 were used for seismic analysis, guaranteeing
a homogeneous catalog for both study periods. Accordingly, earthquakes smaller than ML1.3 were removed to avoid the over-detection
of events at broadband stations as compared to short period seismic
stations. From Fig. 4 it is possible to observe that only a small portion
of 2001 had a Mc higher than 1.3; the remaining Mc values are lower
than 1.3. This means that a low cut off value of ML = 1.3 is reasonable
to homogenize and complete the seismic catalog from 2000 to 2015,
ranging from 1.3 to 4.7 ML. Smaller values of ML may bias the seismic
analysis for some volcanoes where new broad-band stations have
been deployed through time.
Fig. 3. Time series of geophysical and geochemical parameters for each volcano. Color bars
represent volcanoes. Vertical axes are normalized units with respect to the maximum
value, except for SO4/Cl and pH. Right vertical axes of SO4/Cl time series corresponds to
SRV.
The seismic networks are sufficiently similar for both study periods.
Although the number of seismic stations increased over time, and some
of the sensors were changed from short-period to broad-band during
2007–2015, any additional or upgraded stations were located in the
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Table 1
Main changes observed for geophysical and geochemical parameters at CBCMVC for the period 2000–2015. NRV: Nevado del Ruiz, CMV: Cerro Machin Volcano, CBV:Cerro Bravo, NQV: Nevado del Quindío volcano, NTV: Nevado del Tolima volcano,
SIV: St. Isabel volcano, SRV: St. Rosa volcano, and CEV: Cerro Espana volcano.
Year
2000
Main
Background activity at
changes CBCMVC
observed
2001
Background activity
at CBCMVC
2003
Background activity at
CBCMVC
2004
Background activity at
CBCMVC
2005
CMV
Small increase in
earthquakes at CMV
(volcano-tectonic
earthquakes)
2006
Background activity at
CBCMVC
2013
SIV
Large and deep (20 km)
deformation source,
close to Santa Isabel
Volcano (SIV) detected
by InSAR analysis
(Lundgren et al., 2015a,
2015b).
NRV
High seimicity and SO2
flux at NRV.
December 2013.
Earthquake swarm of
volcano-tectonic
earthquakes, located 5
2014
January–December 2014.
Increase in seismic
activity at NRV, NTV,
NQV, SIV, SRV, CEV.
CMV
June 2014. Earthquake.
Depth = 190 km.
ML = 4.4. Located 5 km
SE of CMV.
km. ML = 4.0, Located 6
km) beneath the active crater.
Hydro-thermal activity. No
eruption.
2008
CBV
April 2008. Increasing
CO2 emission (5% vol)
and Radon (N1000
pCi/L) in soil at CBV.
PSRV
September 2008.
Earthquake, depth =
133 km. ML = 5.8.
Located 15 km W of
CBCMVC, close to SRV.
CMV
November 2008.
Earthquake, depth = 4
km. ML = 5.7. Located
few km W of CMV.
CBV
December 2008. Deep
LP (DLP) seismicity at
CBV.
2009
NRV
November 2009.
Earthquake swarm
of volcano-tectonic
earthquakes,
located 5 km e W of
NRV. Depth = 6-7
km
2010
March 2010. Earthquake. Depth
= 120 km. ML = 4.9. Located 15
km W of CBCMVC.
CMV
Deep (15-20 km) persistent
seismicity located 5 km SE of
CMV.
NRV
January–September 2010.
Increase in SO2 flux at NRV,
reaching high values in October
(N5000 Ton/day).
NQV
November 2010. Increase in rate
of shallow seismicity at NQV
2011
SIV
Large and deep (20 km)
deformation source,
close to Santa Isabel
Volcano (SIV) detected
by InSAR analysis
(Lundgren et al., 2015a,
2015b).
2012
SIV
Large and deep (20 km)
deformation source,
close to Santa Isabel
Volcano (SIV) detected
by InSAR analysis
(Lundgren et al., 2015a,
2015b).
NRV
Local deformation at
NRV. March April,
May–June. Increase in
seismic activity and SO2
flux at NRV. Two small
phreato-magmatic
eruptions.
km W of NRV. Depth =
2007
NTV
January 2007.
Earthquake. depths b10
km W of NTV.
CMV
April 2007. SO2 flux at
CMV = 30 Ton/day.
NRV
June 2007. SO2 flux at
NRV = 370 Ton/day
November 2007. About
50ur of deformation at
NRV
2015
January–September.
2014. Increase in seismic
activity at NRV, NTV,
NQV, SIV, SRV, CEV.
NRV
April 2015. Earthquake
swarm of
volcano-tectonic
earthquakes, located 5
km W of NRV. Depth =
NRV
Local deformation at
NRV.
High SO2 flux at NRV
Sep. 2014. Earthquake
swarm of
volcano-tectonic
earthquakes, located 5
6-7 km
CMV
km W of NRV. Depth =
Increase in helium
6–7 km
isotope at CMV
(Inguaggiato et al., 2014)
6–7 km
Local deformation at NRV
High SO2 flux at NRV.
J.M. Londono / Journal of Volcanology and Geothermal Research 324 (2016) 156–168
2002
NRV
April–June, September 2002.
Increase in rate of volcanic
earthquakes (Hybrids) at NRV,
located at shallow depths (b2
J.M. Londono / Journal of Volcanology and Geothermal Research 324 (2016) 156–168
161
Fig. 4. Completeness Magnitude (Mc) for the study period. Mc was calculated using Maximum curvature method, using a sampling window of 500 data points with an overlap of 4. Vertical
bars represent the standard deviation.
near-field (at NRV and CMV) to improve hypocenter precision inside
that particular volcanic network, but would have little effect on the
seismic hypocenters at other volcanoes and on a more regional scale.
I.e. the azimuthal coverage of the entire seismic network at CBCMVC
did not change significantly with the introduction of new near-field
stations inside a particular volcano's network, such as at NRV and
CMV. Furthermore, earthquakes with ML N 1.3 were well detected and
well located during the entire 2000–2015 period (the seismic network
that was deployed between 2000 and 2006 in the CBCMVC had a total
of 20 permanent seismic stations). Robustness of the pre-2007 network
was tested by removing the new stations that were installed after 2007
(26 additional stations in 2015), and relocating all the earthquakes from
2000 to 2015. The hypocenters remained in the same place, with little or
negligible variation. Therefore, I consider that any changes in observed
seismicity are not an effect of changes to the seismic network configuration, but are due changes to volcanic activity at CBCMVC during this
time.
No earthquakes with ML N 4.5 were recorded between 2000 and
2006 at the CBCMVC (SGC, National Seismic Network reports and database http://seisan.sgc.gov.co/RSNC/index.php/consultas/consulexp).
However, several earthquakes with ML N 4 were recorded after
2007 at the CBCMVC. Here I shall describe some of the most relevant
earthquakes: On June 2007, an earthquake with ML = 4.0 and
depth b 10 km, was located 6 km W of Nevado del Tolima volcano
(NTV) (Fig. 1). In November 2008, an earthquake of ML 4.7 (depth =
4 km) occurred at Cerro Machín volcano (south of CBCMVC). In November 2009, December 2013, September 2014, and April 2015, earthquake
swarms were located 5 km W of NRV at 6 km depth. This seismogenic
location has been reported as a precursor to increasing activity at NRV,
and was active before eruptions on November 1985, September 1989,
and periods of minor ash emissions (Londoño and Sudo, 2003). Changes
in seismicity were observed at Cerro Bravo volcano (CBV) on December
2008, when several deep long period (DLP) earthquakes were
registered beneath it. These changes in seismicity across the CBCMVC
suggest a change in behavior of seismogenic processes beneath the
CBCMVC after 2007.
In addition, two earthquakes at possible mantle depths were recorded just beneath the CBCMVC; one occurred on September 2008, with ML
5.7 (depth = 133 km), at about 15 km W of the CBCMVC, close to the
Paramillo de Santa Rosa volcano (PSRV); and the other occurred in
March 4, 2010, with ML 4.9 (depth = 120 km), located 15 km W of
CBCMVC. It is uncertain if these two deep earthquakes affected the
volcanic activity at CBCMVC, but it is worth mentioning the presence
of such unusual seismicity simultaneously with an increase in crustal
seismicity in that region. Due to the uncertainty of its effect on the
volcanic activity, these two earthquakes were not included in the
analysis and calculations.
For seismic data (ML N 1.3) it is interesting to note a migration of
earthquake locations from the edges of the CBCMVC to the more central
regions. Cerro Bravo volcano (CBV) and Nevado del Tolima volcano
(NTV) are both located close to the northern and southern borders,
respectively, both had higher seismicity rates between 2000 and 2006,
while after 2007 seismicity increased at those volcanoes located in
between the CBV and NTV (Figs. 3 and 5).
Fig. 5 shows the hypocenter distribution for earthquakes with
ML N 1.3 for both study periods, 2000–2006 and 2007–2015. It is
possible to observe an important change in the seismicity between
the two study periods. For the period 2007–2015 there is increased
seismic activity at NRV and CMV, as well as Santa Isabel volcano
(SIV), Santa Rosa volcano (SRV), and Cerro España volcano (CEV).
These last three volcanoes have not had any significant seismicity
over the previous few decades. In the earlier study period (2000–
2006), seismicity was focused around NRV, CMV, CBV and NTV, with
a few deeper (N10 km) earthquakes located around the volcanic complex (possibly associated with tectonic faulting). To demonstrate
more clearly the change in seismicity between these study periods
the seismic energy release (E) was calculated for each volcano using
the magnitude-energy relation: Log10(E) = 1.5 ML + 4.8. Then, the
cumulative value of seismic energy (Ce) with time was obtained as
the progressive summation of all the available seismic energy data
for each volcano (Ce = ΣE) from 2000 to 2015. Fig. 6 shows the cumulative seismic energy release for earthquakes ML N 1.3 for each volcano
for the entire study period, and for all the volcanoes combined for
both periods. Fig. 6 demonstrates that the seismic energy released
for the period 2007–2015 was two orders of magnitude larger than
during the 2000–2006 period.
3.2. Deformation
Unfortunately, there is not a complete catalog of electronic tiltmeter
data for the period 2000–2006, but the available data from the dry
tiltmeter network at NRV, CMV CBV, as well as some short vector
leveling profiles (precision leveling) and EDM data, suggest that no important deformation was observed at CBCMVC during this time (SGC,
2007), with values within measurement error. This is in agreement
with the low activity of those volcanoes during 2000–2006, except for
NRV, for which shallow seismic activity in 2002 and 2003, was associated with the hydrothermal system (SGC, 2003).
On the contrary, changes in deformation, by using electronic tiltmeter networks were detected locally for NRV, CMV and NTV
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J.M. Londono / Journal of Volcanology and Geothermal Research 324 (2016) 156–168
Fig. 5. Hypocenter distribution of crustal earthquakes for the period 2000–2006 (a) and 2007–2015 (b). Red solid line represents the NS profile direction. Filled squares represent seismic
stations used for hypocenter location. Green and black lines represent geologic faults. Triangles and numbers represent volcanoes (see Fig. 1 for names).
(Ordoñez et al., 2015; SGC, 2012, 2013, 2014), and at regional scales
in other volcanoes by using InSAR interferometry (Lundgren et al.,
2015a, 2015b) for the period 2007–2015. Fig. 7 shows the time series
of electronic tiltmeters at NRV, CMV, and NTV during the 2007–2015
period (SGC, 2015a, 2015b), as well the location of those tiltmeters
and a zone of possible regional deformation for the CBCMVC detected by InSAR interferometry by Lundgren et al. (2015a, 2015b). Fig. 7
shows that changes in deformation occurred during the period
2007–2015.
A change in local deformation occurred at NRV in 2007 (Ordoñez
et al., 2012). Then in 2009 another deformation episode took place
(SGC, 2009). This was followed by low energy seismicity located W of
NRV. Local and shallow (b2 km depth) deformation (2007–2015) was
about 4 times larger at NRV than CMV, CBV and NTV (Fig. 7b), while
deeper and wider deformation (2011–2015) was larger and closer at
SIV during this time (Lundgren et al., 2015a, 2015b). This pattern suggests that different sources of deformation are acting at CBCMVC at
the present.
Lundgren et al. (2015a, 2015b) suggested that for the period 2008–
2011 no deformation was detected at CBCMVC by using ALOS PALSAR
interferometry, but for the period 2011–2014 by using InSAR interferometry, a change in deformation was detected in a wide zone covering
several volcanoes of the CBCMVC, with a center to the NE of SIV and to
the SW of NRV, at a depth of about 14 km. It is interesting to note that
while local shallow deformation at NRV was detected by an electronic
tiltmeter network for the period 2007–2009, ALOS PALSAR did not detect those changes. It is possible that the presence of an ice cap at
NRV, and the shallowness of the deformation source (b2 km depth;
SGC, 2009), did not enable good results for ALOS PALSAR interferogram
(see Fig. S2 of Lundgren et al., 2015a, 2015b).
J.M. Londono / Journal of Volcanology and Geothermal Research 324 (2016) 156–168
163
Fig. 6. Cumulative seismic energy release for the earthquakes of Fig. 5 with ML N 1.3 for CBCMVC. a) Cumulative seismic energy release for each volcano. Right vertical axis corresponds to
Ruiz (NRV), Machin (CMV), C. Bravo (CBV) and Tolima (NTV) volcanoes. Left vertical axis corresponds to C. Espana (CEV), St. Isabel (SIV), N. Quindio (NQV) and St. Rosa (SRV) volcanoes. b)
Cumulative total seismic energy release for the two study periods for all volcanoes. Left Y axis and lower X axis correspond to 2000–2006 period, and right Y axis and upper X axis
correspond to 2007–2015 period. Note that cumulative seismic energy release for the period 2007–2015 is almost two orders of magnitude N2000–2006 period. Seismic energy
(E) was calculated according Guttenberg and Richter formulation (Log10(E) = 1.5 ML + 4.8).
Despite these discrepancies, it is important to note that a wide deep
intermittent deformation source is present beneath the CBCMVC, as
well as other shallower localized deformation sources. Based on the
concurrence of increasing seismicity at most of the same places where
those deformation zones are present, such deformation could be attributed to new magmatic activity in this area. The extension of the deep
deformation zones surrounding several volcanoes is suggestive of an ascending magma body affecting not only the seismic activity, but also the
geochemical behavior of those volcanoes, as it is observed particularly
from 2010 to 2015.
3.3. Geochemistry
Changes in gas geochemistry and hydrochemistry were observed on
several volcanoes from 2007 onwards as well. CBV showed an increase
in CO2 and Radon emissions in soil in March and April 2008 (Figs. 1 and
3). Radon gas in soil showed an increase from 2008 to 2012 for NRV,
CMV and CBV as well. A decrease in pH was detected at NRV and NTV
between 2009 and 2012 (Figs. 1 and 3)0.1 At NRV some stations (2.5
and 8 km away from the active crater) reached pH values as low as
0.9 in 2010 (SGC, 2011). Moreover, an increase in SO4/Cl ratio was
observed at SRV in 2013 and 2015, and CMV in 2013 (Figs. 1 and 3).
All pH and SO4/Cl values were measured at hot springs close to the volcanoes (Fig. 1). It is worth of mention that the source of those waters at
NRV was previously associated to magmatic gases at depth (Sturchio
et al., 1988).
From 2000 to 2006, SO2 was detected in very small amounts, at
CBCMVC from satellite (NASA GES DISC) and increased after 2012
(Fig. 3). SO2 data available from DOAS instruments also showed temporal changes; In June 2007, a measurement using mobile DOAS instrument showed a value of about 370 Ton/day for NRV. Interestingly
small amounts of SO2 flux were detected at CMV in April the same
year, by using the same mobile DOAS instrument, with about 30 Ton/
day of SO2. Importantly, this was the first time ever that SO2 was detected at Cerro Machin volcano (SGC, 2007) since gas monitoring sampling
began in 1989. During 2008 and 2009 small amounts of SO2 were detected at NRV. Regular measurements were taken from the end of
2009 onwards when DOAS instruments were deployed permanently
at NRV. Early in 2010, an increase in SO2 emissions was detected at
NRV, eventually reaching values N20.000 Tons/day in 2012. In general,
SO2 emissions were highly variable, ranging from few thousand Tons/
day up to several thousands (20,000–30,000 Ton/day), a trend that
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J.M. Londono / Journal of Volcanology and Geothermal Research 324 (2016) 156–168
Fig. 7. a) Deformation (tilt) observed at NRV (grey), CMV (Red), NTV (green) and CBV (Blue) from electronic tiltmeters from 2007 to 2015. Resultant vectors are shown for each station.
b) Accumulated total observed deformation (absolute values of resultant vectors including inflation and deflation) at NRV, CMV NTV and CBV. Left vertical axes corresponds to NRV; right vertical axis corresponds to CMV, NTV and CBV c) Location of tiltmeters (black circles), volcanoes (white triangles) and deformation zone (dashed line) observed at CBCMVC by Lundgren et al.
(2015a, 2015b) by using InSAR interferometry. Deformation zone taken from an interferogram courtesy of Sergey Samsonov (see Lundgren et al., 2015a, 2015b for details). CBRAVO tiltmeter is
not plotted (Latitude = 5.0229° N; Longitude = 7.5298° W).
continues today since 2010. Fig. 8 shows accumulated SO2 flux emissions and seismicity at NRV from 2010 to 2015. On some occasions
SO2 release is associated with increasing seismicity, however, often it
is not.
In addition, a clear change in the magmatic signature in the shallow
fluids was observed at CMV during the period 2007–2015. During two
sampling campaigns, two measurements of helium isotopes were
taken during 2011 and 2013 at CMV. The value of the helium isotope
was 4.61 R/Ra, measured in 2011, while the helium isotope reached a
value of 5.65 R/Ra in 2013. Simultaneously with the change in helium
isotope data, a decreasing of log C/3He ratio from 10.81 to 10.76 was
also observed. Such changes in geochemistry suggest magmatic activity
at CMV between 2011 and 2013 as was proposed by Inguaggiato et al.
(2014, personal communication).
Fig. 8. Cumulative SO2 flux (from DOAS instruments) and cumulative number of earthquakes at NRV from 2010 to 2015. VT = volcano tectonic earthquakes. LP = long period earthquakes.
J.M. Londono / Journal of Volcanology and Geothermal Research 324 (2016) 156–168
4. Discussion and concluding remarks
Geophysical and geochemical changes from 2007 to 2015 at the
CBCMVC suggest that possible new magmatic input is currently occurring in that region, and is affecting various volcanic centers. It is interesting to note that these changes are neither simultaneous nor occur at one
particular volcano, but rather they occur at different times and places
throughout the CBCMVC. Moreover, these changes in geophysical and
geochemical parameters do not occur at the same time as changes or
improvement in the monitoring networks. Thus, supporting the hypothesis that these changes are associated with volcanic activity rather
than an artifact of monitoring networks. The observations presented in
this study indicate magmatic signals from deep sources. Geochemical
sampling in 2011 at CMV (Inguaggiato et al., 2014); the magmatic origin
of SO2 flux at NRV since 2012; a deep source of deformation in between
several volcanoes of CBCMVC from 2011 to 2013 (Lundgren et al.,
2015a, 2015b) and an increase in the seismicity in almost all volcanoes
of the volcanic complex not associated with configuration or improvement of seismic networks, among other changes all suggest that new
magma is ascending beneath the CBCMVC.
The most affected center until now is NRV. One of the possible reasons for why NRV is currently the most active volcano of the CBCMVC
can be because NRV is the only open system within the complex. Geomorphology, recent activity, and monitoring data suggest that other
volcanoes of the CBCMVC remain closed systems. It is possible that in
the near future, some of those volcanoes become open systems, and
that the magmatic activity occurring deeper within the volcanic complex will manifest at the surface as eruptions, ash or gas exhalations.
For the purposes of this study an open volcanic system is defined as a
volcano with permanent or semi-permanent open conduits; with
fumarolic or gas activity releasing into the atmosphere; and with
eruptions that vary on a time-scale of days to decades. A closed volcanic
system is a volcano with sealed conduits; with very little emission of gas
into the atmosphere; and with no eruptions over a long time-scale
(centuries or more). Other authors have different definitions for an
open volcanic system and this remains an open question, however a
central theme to all definitions of open-vent volcanism is that of an
established conduit that facilitates eruption, and can respond quickly
to changes in the magmatic or hydrothermal system (Jaupart, 1998;
165
Sparks, 2003; Morales et al., 2010; Chaussard et al., 2013; Rodgers
et al., 2015).
As mentioned previously, CBV registered a sequence of DLP seismicity on December 2008. N35 DLP earthquakes were recorded on 30th
December (Fig. 9). DLP events were characterized by low frequencies,
ranging from 1.8 to 2.8 Hz. This seismicity was preceded by an increase
in CO2 and radon gas in soil emission in April 2008, at several stations
close to CBV. DLP seismicity has been associated with deep magma
movement (White, 1996; Chouet and Matoza, 2013; Power et al.,
2012). Fig. 9 shows temporal change in radon and CO2 in soil and location of some of those DLP events. The CO2, probably of deep origin, may
be related to the degassing of a deep magma body (30 km depth,
Londoño and Dionicio, 2011; Londoño, 2015), and the DLP events may
be the result of such magma or gas movement at depth. It is interesting
to note that an increase in radon emission (and CO2) was also detected
at CMV from March to May in the same year 2008 (Fig. 3). However, it is
uncertain if this increase in radon at CMV is related to the further increase in radon and CO2 at CBV, or with the subsequent occurrence of
DLP seismicity. Two CO2 field campaigns in 2013 and 2014 at CMV
using a flow meter with a cumulative camera system and a LICOR sensor
(SGC, 2013, 2014), showed high values of CO2 of up to 700,000 ppm at
some places where vegetation and birds were killed. This high release
of CO2 at CMV is believed to come from a deep magmatic source located
at about 15 km depth based on CO2 isotopes (δ13C of CO2) study
(Inguaggiato et al., 2014). This also suggests that deeper magmatic
sources are acting at CBCMVC.
Werner et al. (2012) suggested that CO2 and SO2 flux several months
prior to the 2009 eruption of Redoubt volcano were associated with
magma degassing; although the depth at which that degassing occurred
was not well established, the presence of DLP earthquakes (25–38 km
depth; Power et al., 2012) and deep deformation sources let them to
conclude that the origin of such gases were from a deep magma source.
It is possible that a similar situation can be occurring at CBCMVC, but not
as accelerated in time as at Redoubt volcano.
On the other hand, NRV showed an important increase in seismicity
in 2010 that persists to time of writing (May 2016), with N 250,000
volcanic earthquakes recorded between 2010 and 2016. Concurrently,
seismic activity was extended to other volcanoes of the complex
(Figs. 3, 5 and 6). One possibility of this phenomenon is the transfer of
Fig. 9. a) Temporal changes in CO2 and Radon gas in soil at Cerro Bravo volcano (CBV) at two stations (CBRA-1 dashed lines, CBRA-2 solid lines) associated with DLP seismicity. b) Location
of stations and some DLP seismicity occurred on 30th Dec. 2008. Rhomboids represent radon and CO2 soil stations (both located at same place). Filled squares represent seismic stations.
Black triangle represents volcano. Filled circles represent hypocenters of DLPs.
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J.M. Londono / Journal of Volcanology and Geothermal Research 324 (2016) 156–168
Fig. 10. Spatial and temporal variation of seismicity at NRV. a) January 2010–July 2012. b) August 2012–Dec. 2015. Plotted earthquakes with ML N 1.0.
stress from NRV to the active faults surrounding the volcano (Castaño et
al., 2011); but volcanoes such as CMV and CBV are a long way from NRV,
and showed increasing seismicity in 2008 and 2009, before the reactivation of NRV in 2010. This supports the idea that wider and deeper magmatic activity was occurring at CBCMVC from 2007 onwards, and not
localized only at NRV or close to it. As was pointed out by Lundgren
et al. (2015a, 2015b), it is possible that other volcano sources can be responsible for the wide deformation observed in the region close to NRV,
for the period 2011–2013 (see below). On the other hand, it is interesting to note that the relationship between seismicity and SO2 flux shows
a similar trend from 2010 to the beginning of July 2012 for NRV. After
that date, the SO2 flux stabilized but the number of volcano tectonic
earthquakes (VT) and long period earthquakes (LP) continued to
change, (Fig. 8). This change is possibly associated with a change in volcanic activity. From that date (July 2012) onwards, VT earthquakes were
located far from the active crater and increased in number, while the
number of LP earthquakes occurring at the active crater decreased.
The observed changes in seismicity are possibly associated with
magma intrusion pulses, located N 7 km depth and to the NW of NRV.
Fig. 10 shows this change in seismicity at NRV. This could mean that
other sources of magma are responsible for the SO2 flux rather than
the shallow magma system at NRV (Stix et al., 2003). Moreover, relatively high SO2 flux rates released by NRV continuously since 2004
(Fig. 3) with no associated large eruption (passive degassing), are suggestive of SO2 influx from a deep magma chamber, possibly basaltic,
as being responsible for the excess sulfur, as was pointed out by
Shinohara (2008).
Additionally, strong evidence of magma ascent at CBCMVC is the recent observation of a small lava dome that has extruded at the surface of
NRV since September 2015, and continues to grow until time of writing
(March 2016). This new dome was detected by the Italian Space Agency
(ASI) COSMO-SkyMed radar slant-range, with an estimated pseudovolume of 12,000 m3 (Lundgren et al., 2015b; SGC, 2015b). This dome
seems to be the surface manifestation of the change in seismicity
observed since 2010 at NRV.
Similarly, at CMV spatial distribution of seismicity also changed.
From 2000 to 2008, seismicity was concentrated primarily at the main
dome inside the crater, but from 2009 to 2015, a shift in the seismicity
Fig. 11. Spatial and temporal variation of seismicity at CMV. a) January 2000–Dec. 2008. b) January 2009–Dec. 2015. Plotted earthquakes with ML N 1.0.
J.M. Londono / Journal of Volcanology and Geothermal Research 324 (2016) 156–168
167
depth seismicity (15–30 km depth) throughout the volcanic complex
except for in the CMV area (Figs. 5b, 11). Our current study of temporal
variations of seismic velocities from seismic 3D tomography of P and S
velocity for CBCMVC, aims to detect possible temporal changes related
to the suggested new magmatic activity.
In the last two centuries, no large eruption (N5 VEI) has taken place
at CBCMVC (Méndez, 2003), but the potential is high, based on the geological record of several volcanoes of that complex (Méndez et al., 2002;
Regnier, 2014). NRV and CMV are two dangerous active volcanoes. The
last important eruption of NRV (VEI = 3) was on November 1985.
Although it was small, N 23,000 people were killed by a lahar. The last
eruption of CMV was about 900 years ago; geological records show
that there is a significant eruption at this volcano approximately every
900 years (VEI N 5; Rueda, 2004). Given this background, it is crucial
that any hint of increasing activity at the CBCMVC is considered carefully. According to Phillipson et al. (2013), any change of any geophysical
or geochemical variable above a predetermined background level,
should be considered as unrest in a volcano.
Based on this, I suggest that CBCMVC is in a state of unrest, with several volcanic centers showing signs of activity that must be considered
in the hazard and risk assessment of this region of Colombia. A rough estimation indicates that N 3 million people (DANE, 2012) live close to
those volcanoes and could potentially be affected by their awakening.
Acknowledgements
Fig. 12. P-wave velocity profile (a) and cross section of spatial mapping of b-value (b) of
Central Colombia (Lat = 4.7° N). Configuration of tectonic plates and possible location
of deep magmatic chambers of CBCMVC. a) Colors represent velocity (km/s) and contours
represent velocity perturbation (%). b) Colors represent b-value and contours represent
standard error of b-value. Fig. 12a modified from Londoño and Dionicio (2011). Fig. 12b
modified from Londoño (2015). Numbers represent volcano locations: 1:C. Machín, 2:N.
Quindío, 3:St. Rosa, 4:St. Isabel, 5:N. Ruiz, and 6:C. Bravo. Dashed circles represent the possible deep magmatic chambers of CBCMVC.
was detected towards the SE and events became deeper, changing from
3 to 5 km depth at the crater to 15–20 km depth to the SE. Fig. 11 shows
the change in spatial distribution of seismicity at CMV. This change in
spatial distribution in seismicity supports the idea that new magmatic
activity is occurring beneath CBCMVC, and not only at NRV.
Other possible evidence of magmatic activity at CBCMVC is the presence of a deep magmatic chamber beneath the complex. Based on a
study of regional 3D tomography of seismic velocity, Londoño and
Dionicio (2011), suggested that deep magmatic bodies are emplaced
at CBCMVC at about 20–40 km depth. Moreover, Londoño (2015), observed a zone with high b-values almost at the same location (beneath
CBCMVC) of the low-Vp values of Londoño and Dionicio (2011). Fig. 12
shows a profile located at latitude 4.7° N, showing the results of seismic
3D tomography of P-wave velocity with a resolution of 30 × 30 × 10 km
and a cross section in the same direction with the results of spatial mapping of b-values with a resolution of 5 × 5 × 5 km. This figure shows a
zone with low-velocity for P-wave and high b-value, just beneath the
CBCMVC. This zone is associated with the deep main source of the
magma supply for the active volcanoes at CBCMVC. It is known that
deep magma can ascend, and that some portions of such ascent is
aseismic (Chouet and Matoza, 2013; Kumagai et al., 2003). This suggests
that the seismicity observed until now at CBCMVC, which is continuous,
and at high levels from time to time, is indicative that magma is moving
upward, and probably at different depth levels, from deep (20–40 km)
to relatively shallow depths (2–3 km), with some aseismic gaps at
some depths. Moreover, this can explain why there is no intermediate
The author would like to express his gratitude to his colleagues at
Servicio Geológico Colombiano, specially to Ricardo Méndez, Lina
Castaño and Beatriz Galvis for their helpful comments and suggestions.
This work also benefited from fruitful discussions and comments from
Luca Caricchi and Mel Rodgers. Two anonymous reviewers improved
considerably the final manuscript. This research was supported by the
Project "Research and Monitoring Colombia active volcanoes",
Geohazards technical direction of Servicio Geologico Colombiano (CGS).
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