SPECIAL ISSUE

Structural controls on the occurrence and morphologyof karstified assemblages in northeastern Vietnam:a regional perspective

Hai Thanh Tran • Bat Van Dang • Chi Kim Ngo •

Que Dinh Hoang • Quyen Minh Nguyen

Received: 1 July 2010 / Accepted: 4 April 2011

� Springer-Verlag 2011

Abstract Karstified assemblages occur widely in, and

distinctively shape, the geological landscape of the north-

eastern part of Vietnam. These carbonate rocks were

deposited during three major periods of basinal evolution

including: (1) Late Cambrian, (2) Early Devonian to Early

Carboniferous, and (3) Carboniferous to Earliest Triassic.

These sedimentary units contain primary sedimentary

structures and have undergone numerous post-depositional

geological processes including multiple deformational

events, which can be regionally correlated. Several

thrusting events and associated folding have led to signif-

icant thickening of the carbonate units. The subsequent

post-thrusting cross-folding events, followed by several

phases of brittle faulting and fracturing further modified the

spatial geometry and outcrop of these rocks. The combi-

nation and interaction of the primary structures with those

formed during the long-lived and complicated deforma-

tional history is an important controlling factor in local and

regional hydrogeological systems in the region. The geo-

logical structures now recorded in the carbonate units

ultimately govern the formation of the unique modern

surface and sub-surface geomorphology of the karstic ter-

rains in northeastern Vietnam. These structures should be

further investigated in the context of water resource

assessment and natural hazard prediction and mitigation.

Keywords Karst � Structural control � Groundwater �Northeastern Vietnam

Introduction

The northeastern part of Vietnam, which covers parts of Yen

Bai, Tuyen Quang, Ha Giang, Thai Nguyen, Bac Kan, Cao

Bang, Lang Son, Quang Ninh, and Hai Phong provinces is

underlain by numerous rock types of varying composition,

ages and environments (Tran Duc Luong and Nguyen Xuan

Bao 1982; Tong Duy Thanh and Vu Khuc 2006; Tran Van

Tri and Vu Khuc 2009), which have undergone numerous

phases of tectonic deformation that extended from at least

from middle Paleozoic to present (Tran Thanh Hai 2009).

Previous geological works show that large parts of the area

are covered by thick and strongly karstified sedimentary

packages (Tran Duc Luong and Nguyen Xuan Bao 1982; Do

Tuyet 1998; Figs. 1, 2). These rocks comprise mostly car-

bonate associations that are intercalated with subordinate

terrigeneous and/or siliceous members. They were formed

during a long history of geological evolution, from Early

Cambrian to late Mesozoic and were variably deformed by

numerous regional deformational events, which have

resulted in the thickening and fragmentation or dismem-

berment of the rock units. It has been recently proposed that

the development of the unique karstified landscape in

northeastern Vietnam is the consequence of a combination

of composition, deformation (Tran Thanh Hai et al. 2004;

Tran Thanh Hai 2009) and recent exogenic processes under

heavy influence of tropical monsoon climate (Dang et al.

2009). In addition, the nature of both regional and local

hydrogeological systems related to the infiltration, migration

and storage of groundwater within such a unique landscape

(Nguyen Van Lam et al. 2009; Vu Thanh Tam et al. 2009)

are governed by the interaction between rock bodies and all

secondary geological processes.

The combination of endogenic and exogenic processes

has formed a natural spectacle within the karstified terrains

H. Thanh Tran (&) � B. Van Dang � C. Kim Ngo �Q. Dinh Hoang � Q. Minh Nguyen

Department of Geology,

Hanoi University of Mining and Geology,

Hanoi, Vietnam

e-mail: tranthanhhai.humg@gmail.com

123

Environ Earth Sci

DOI 10.1007/s12665-011-1057-1

of northeastern Vietnam and adjacent areas (Ta Hoa

Phuong et al. 2009; Tran Tan Van et al. 2009; Truong

Quang Hai 2009; Le Duc An and Uong Dinh Khanh 2009;

Li Zhengping and Liang Younging 2004; Li Yuhui et al.

2004), which includes the world-famous Ha Long Bay (a

UNESCO Natural Heritage site) and a World Geopark in

Ha Giang. However, the karstic regions are also vulnerable

and subject to natural hazards in which the most severe

impacts are from the collapse of structures, sink holes,

water pollution caused by groundwater action and cavern

development (e.g., Vu Thi Minh Nguyet and Goldscheider

2006; Canh et al. 2009; Dang Huu Diep and Hoang Thi

Hong Hanh 2009, Yuan Daoxian 2009; Dang et al. 2009).

As a very large population in northeastern Vietnam

resides within the karst areas, the constant shortage of

water resources and the abundance of natural hazards in

such areas commonly lead to negative affects on the well-

being of local communities as well as social economy (Vu

Thi Minh Nguyet and Goldscheider 2006; Dang et al. 2009;

Canh et al. 2009; Dang Huu Diep and Hoang Thi Hong

Hanh 2009). However, the importance of geological

structures within the carbonate units that govern the for-

mation and/or development of karst and its hydrological

systems, and in particular the controlling factors for

groundwater resources in northeastern Vietnam, have to

date not been thoroughly addressed. In order to more fully

understand the nature of karst landforms and their associ-

ated natural resources and hazards in northeastern Vietnam,

a comprehensive, multidisciplinary and qualitative research

program must be carried out. However, available data can

be used for a preliminary study of these karstified terrains.

This paper reviews the general geological features of the

carbonate associations in northeastern Vietnam and their

significance as regional controlling factors in the occurrence

and formation of karst morphology. These current geological

interpretations for the region can be used as indicators for the

assessment of groundwater resource and prediction and

mitigation of natural hazards in karstified areas.

General geological features of karstified assemblages

in northeastern Vietnam

Stratigraphy of karstified rocks

Northeastern Vietnam is underlain by thick carbonate

successions, which were deposited during a long and

complex geological history (Tong Duy Thanh and Vu Khuc

2006; Tran Van Tri and Vu Khuc 2009). On the basis of

presently available data (Tong Duy Thanh and Vu Khuc

2006; Tran Van Tri and Vu Khuc 2009), carbonate rocks in

northeastern Vietnam can be subdivided into several suc-

cessions (Figs. 1, 2).

The oldest carbonate successions recorded in the north-

western most part of northeastern Vietnam comprises thinly

to thickly bedded rocks of Late Cambrian age (Figs. 1, 2).

The composition of the rocks is variable, from thinly lay-

ered limestone intercalated with marl and/or siliceous

members to thick-bedded, homogeneous carbonate units

(Fig. 3a). These rocks are commonly dismembered, fault-

bounded and locally metamorphosed (Fig. 2) owing to

multiple deformations including flattening, shearing, thrust-

faulting and folding (Fig. 3b; Tran Thanh Hai 2009).

The second carbonate succession, which was deposited

from Early Devonian to Early Carboniferous (Tong Duy

Thanh and Vu Khuc 2006), is widespread in the far

northeastern and southeastern portions of northeastern

Vietnam (Figs. 1, 2). Its composition varies greatly from

thick-bedded or massive limestone (Fig. 3c) to thinly lay-

ered, immature carbonate units that are commonly inter-

calated with marl, chert, and local manganese-bearing

layers (Fig. 3d). Similar to the Late Cambrian carbonate

Fig. 1 Summarized stratigraphic column of various parts of north-

eastern Vietnam, showing the stratigraphic position of major karstic

assemblages and their relationship with other units and time: (1) non-

deposition, (2) siliciclastic rocks, (3) Late Cambrian carbonate, (4)

Devonian-Early Carboniferous carbonate, (5) Carboniferous-Early

Triassic carbonate. Modified after (Tong Duy Thanh and Vu Khuc

2006)

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123

succession, the Devonian-Carboniferous carbonates were

also affected heavily by tectonic deformation, which

resulted in significant thickening and dismemberment

owing to multiple deformational events (Tran Thanh Hai

2009).

The upper carbonate succession comprises thick units of

Carboniferous to Early Triassic limestone and associated

sedimentary members of various composition that are

regionally widespread in all parts of northeastern Vietnam

(Figs. 1, 2). The lower part of this succession commonly

Fig. 2 Generalized structural

map of northeastern Vietnam,

showing the spatial distribution

of major carbonate successions

and their relationship to non-

carbonate successions as well as

major regional tectonic

structures. Note that most of the

carbonate successions are fault-

controlled and/or are

dismembered by faults

Fig. 3 Examples of field

occurrences of major carbonate

units in northeastern Vietnam:

(a and b) Late Cambrian

carbonate exposed in

northeastern Lao Cai province;

b strongly deformed and

metamorphosed Late Cambrian

carbonate rocks; c Thick- to

thin-bedded Late Devonian

limestone exposed in Cat Ba

Island area, Hai Phong city;

d thin-bedded Early

Carboniferous limestone

intercalated with chert and marl

layers in Cat Ba Island; e, f)Thick-bedded to massive,

homogeneous, strongly

karstified limestone exposes

widely in Ha Long Bay, Quang

Ninh province (e) and Meo Vac

area, Ha Giang province (f)

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123

comprises homogeneous, mostly massive to thick-bedded

limestone (Fig. 3e, f) that is regionally widespread. In

contrast, the upper part of this succession is more hetero-

geneous in composition and includes thinly layered lime-

stone members that are commonly intercalated with

terrigenous deposits (Tong Duy Thanh and Vu Khuc 2006).

These rocks are strongly fractured and dismembered

because of subsequent tectonic deformation (Tran Thanh

Hai 2009).

Structural control on the spatial occurrence

of karstified rocks

Results of recent geological works show that within

northeastern Vietnam, all rocks experienced a multiphase

deformational history, under the ductile, brittle-ductile and

brittle strain conditions, including repeatedly shearing,

folding and fracturing (Nguyen Cong Thuan 2005; Nguyen

Trong Dung 2006; Tran Thanh Hai 2009; Tran Thanh Hai

et al. 2004). Although the exact timing of each deforma-

tional event has not been precisely dated due to the lack of

systematic and qualitative geological works, the deforma-

tional events in northeastern Vietnam can be generally

interpreted to have taken place during numerous phases of

tectonic evolution that extended from Middle Paleozoic to

Cenozoic. As consequence of regional deformation, the

carbonate assemblages within the study area were therefore

variably deformed by different thermo-tectonic regimes

and under differing strain states. Results of such defor-

mational regimes have produced several types of tectonic

fabrics, in which those were formed during earlier phases

of deformation were then repeatedly reactivated or over-

printed by later phases of folding and brittle fracturing

(Tran Thanh Hai 2009; Tran Thanh Hai et al. 2004).

This investigation recognizes that the most strongly

deformed carbonate rocks are part of the Late Cambrian

succession, which were probably affected by an Ordovi-

cian–Silurian regional tectonic event that has been widely

recognized across Vietnam and southern China (e.g., Faure

et al. 2009; Tran Thanh Hai 2009; Tran Van Tri and Vu

Khuc 2009) and consequently led to the uplift and erosion

of the carbonate units and subsequently created a sub-

Devonian regional unconformity prior to the deposition of

the Devonian-Carboniferous association (Fig. 1). This

deformational event led to the formation of regionally

extensive ductile thrust zones and associated isoclinal fold

systems, which resulted in significant tectonic transporta-

tion, over-thickening, repetition or dismemberment of the

carbonate units (Figs. 2, 4a).

Subsequently, all carbonate rocks in northeastern Viet-

nam were affected by several phases of regional defor-

mation, which have been interpreted owing to plate

collisions and terrain assembly to form proto-southeast

Asia during the Mesozoic (e.g., Hutchison 1989; Metcalfe

2005). During these tectonic events, all carbonate rocks

were affected by regionally widespread ductile to brittle-

ductile thrust/reverse shearing and associated folding

(Fig. 2). The overprinting of post-thrusting folding events

on older thrust-related structures has further complicated

structural grain of the carbonate units (Fig. 5a, b).

These earlier formed structures are truncated by several

generations of brittle, reverse, normal and strike-slip

faulting, and extensive fracturing (Fig. 5c) that occurred

during the latest phases of post-orogenic, intra-continental

tectonic activities during the Cenozoic (e.g., Tapponnier

et al. 1986, 1990; Searle 2006; Tran Van Tri and Vu Khuc

2009). The superposition of numerous types of structures

has resulted in a complex regional structural interference

pattern of the carbonate and other rock types (Fig. 2).

The structural pattern described above was then

strongly overprinted by neotectonic and modern exogenic

processes, including regionally extensive weathering,

erosion, water movement and other sub-aerial activities.

The combination of these processes has led to the rapid

destruction of carbonate units, especially along the zones

of structural weaknesses and created the current unique

Fig. 4 a Imbricate structure formed by systematic over-thrusting of

limestone units along shallow-angle thrust-faults that led to the over-

thickening of the Late Cambrian carbonate rocks in northwestern

most part of northeastern Vietnam. b A klippe structure of Early-

middle Devonian limestone (D1–2) developed above the Late Devo-

nian siliciclastic rocks in Trung Khanh area, Cao Bang province. The

special karst morphology was formed by the removal of most of the

limestone in hanging-wall blocks a thrust system (dashed line)

Environ Earth Sci

123

geomorphology of the karstified assemblages in north-

eastern Vietnam.

The role of regional structures on the movement

of groundwater and formation of karst morphology

in northeastern Vietnam

The importance of geologic structures in the formation of

the morphology in karstified rocks has been widely rec-

ognized (e.g., Gremaud et al. 2009; Hauselmann et al.

1999; Gabrovsek and Dreybrodt 2001; Harmon and Wicks

2009; Ford and Williams 2007, and references therein). In

general, karst evolution and its resultant morphology are

controlled by many geological factors, from lithologic

composition, geological structures and physical properties

of the rocks, to the sub-aerial environments in which the

karstified rocks are exposed (e.g., Palmer 1991; Palmer

et al. 1999; Ford 2002, 2006; Ford and Williams 2007;

Klimchouk 2006). Groundwater action to form caves and

subsequent unroofing of caves is a large-scale geomorphic

process that plays an important role in the formation of

karst topography (e.g., Klimchouk 2006).

The infiltration and migration of water in rocks are

generally attributed to the degree of porosity or voids

within the rocks bodies. In carbonate rocks, a wide range of

voids of differing origins affects their capacity to store and

transmit water (e.g., Ford and Williams 2007). In addition,

both primary sedimentary and tectonic structures such as

bedding, high-strain zones, hinge zones of macroscopic to

mesoscopic folds or joint and fracture systems, which are

important elements governing the migration and/or locali-

zation of groundwater within the karst systems, have been

identified (Worthington 1999). Hauselmann et al. (1999)

have demonstrated that the structural setting and tectonic

regime define the overall geometry of the carbonate units

and influence the development of the various phases of the

karst system. The tectonic structures commonly act as

channel systems allowing the migration of water through

the karstified units in which most of the conduits appear to

belong to old, deep phreatic systems (Hauselmann et al.

1999). Gremaud et al. (2009) found that the lateral move-

ment of groundwater in karstified rocks is commonly

stratification controlled, whereas the down-deep or cross-

layering migration commonly occurs along deeply pene-

trating fault systems. Ford (2006), on the other hand, has

emphasized the most common karst patterns are formed by

unconfined meteoric water, which migrates along the

fractures and other structures occurring in the karst rocks.

The northeastern Vietnam karst systems occur in areas

that are dominated by overprinting tectonic structures

derived from multiple regional deformation events (see

above). Numerous zones of structural weakness and/or

high porosity within the rock units created during long-

lived tectonism could act as channels for down-deep

movement of meteoritic water to form present-day karstic

landscapes. On the basis of field observation and structural

interpretation of the relationship between the localization

of karst systems and their hydrological behavior in differ-

ent carbonate units, major controlling factors of geological

structures to groundwater migration and subsequent karst

morphology development in northeastern Vietnam can be

distinguished; the most noticeable elements are summa-

rized in the following.

Primary sedimentary structures include the primary

bedding, the interlayering between carbonates and other

rocks with different permeability, and the unconformable

contact between the carbonate rocks and the underlying or

overlying siliciclastic rocks (e.g., Fig. 6a). The contacts

between layers of differing composition, especially the

unconformable contacts, are zones of potential weakness

and are vulnerable to deformation; they commonly become

Fig. 5 a A large-scale synclinal system formed by deformation of the

Carboniferous-Permian limestone in northeast of Cao Bang province;

b The hinge zone of a large antiformal structure that formed by

refolding of highly strained Late Devonian carbonate rocks in

southeastern margin of Cat Ba Island; c Sub-vertical brittle fractures

developed systematically in bedded Carboniferous-Permian limestone

in Ha Long Bay area. Note that the karst landscape is partly controlled

by the geometry of fold systems or the interaction between bedding

and fracture. See text for discussion

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123

the locus of structural and mechanical failure with a high

degree of fragmentation. Depending on the strain condi-

tion, intense brittle brecciation or ductile mylonitization

can be generated along such contacts, or within the car-

bonate successions occurring adjacent to them. In this case,

significant enhancement of the porosity or void space along

the deformed contact zones could be achieved. Conse-

quently, such highly deformed zones become favorable

environments where water can be concentrated or migra-

ted, promoting the destruction of carbonate rocks (Fig. 6b).

The second important group of structures that play not

only a major role in the formation of the regional structural

grain but also influence the karst development in the car-

bonate units in northeastern Vietnam is the regionally

extensive development of thrust/reverse shear or fault

zones. As discussed earlier, thrust shearing is a very

common feature in northeastern Vietnam as the conse-

quence of Phanerozoic collisional tectonic processes.

Deformation along the thrust zones commonly led to the

formation of highly strained, brittle-ductile, and/or ductile

shear zones of tens of meters in thickness and tens of

kilometers in length. If such zones were formed ductilely

and were not reactivated during subsequent deformation,

they would become efficient confining beds, preventing

water from migration downward. In this case, groundwater

would be localized above such zones, transported along the

hanging wall, ultimately leading to karst formation

(Fig. 6c). One the other hand, if such zones were developed

or reactivated by subsequent brittle deformations, they

would become zones of intense fracturing with high per-

meability, and as such would be favorable channels or

aquifers for groundwater transportation and localization,

subsequently generating regionally extensive karst sys-

tems. In addition, thrust-faulting also led to significant

tilting, thickening and repetition of carbonate units, and the

formation of typical cuesta morphologic feature of the

karstified terrain in northeastern Vietnam (Figs. 3a, c, 4,

6a, c).

Folds are the third and very common type of structures

observed in carbonate units in northeastern Vietnam (see

above, Figs. 2, 5a, b). Regionally superimposed folding at

both macroscopic and mesoscopic scales has produced

numerous anticlinal/synclinal systems in variable orienta-

tions and led to the tilting or the thickening of the

Fig. 6 a An unconformity (dashed white line U) between the thick-

bedded to massive Carboniferous-Permian limestone (C-P, upper) and

Late Devonian siliceous limestone and marl (D3, lower) exposes north

of Pa Vi commune, Ha Giang province. White arrows indicate the

location of cavern developed above the unconformity. The uncon-

formity in this case is the area of ground water migration and/or

discharge. b Idealized geological cross-sections showing examples of

the structural relationship of carbonate rocks with other rock types

and structures and their relationship to the development of karst

systems as well as localization of groundwater found in Meo Vac

area, Ha Giang province. c Outcrop exposure of a thrust fault system

(traced by dashed red lines) developed by over-thrusting of the Late

Cambrian limestone above the siliciclastic rocks and its relationship

to the groundwater discharge area. In this case, the thrust zone

underneath of limestone assemblages acts as a confining bed along

which the groundwater in carbonate rocks is concentrated. Ground-

water occurs at the lowest point of thrust exposure. d Idealized cross-

section showing structural relationship between Triassic siliciclastic

and Carboniferous-Permian limestone in Yen Minh area, Ha Giang

province and the development of cavern and groundwater system. See

text for discussion

Environ Earth Sci

123

carbonate units. The development of penetrative spaced

axial cleavage in competent layers such as carbonate beds,

on the other hand, leads to the strong fragmentation of rock

bodies, which may significantly improve their permeabil-

ity, and therefore either enhance the migration of water

downward or form the reservoir for groundwater within the

carbonate units. In addition, the common tilting of the

carbonate successions in major fold systems further

enhances the downward movement of water along the

geological contacts that are parts of the limbs of the folds.

The combination of the structures formed during folding

events consequently enhanced the action of water within

the karst units and therefore contributed to the complex

karst morphology (Fig. 5).

The intense development of numerous brittle structural

systems in northeastern Vietnam played a vital role in the

behavior of the groundwater systems and therefore led to

the formation of special karst morphology. The brittle

fracturing of the carbonate units is commonly sub-vertical

or steeply dipping, non-penetrative, intense brittle frag-

mentation, and brecciation. They are regionally extensive

and systematically concentrated as sets or systems occur-

ring sub-parallel to, or as part of, major fracture and fault

systems that deeply penetrate into the rock bodies (Fig. 7a,

b). Such fracture systems are highly porous and, in many

cases, produce numerous zones of high permeability that

form favorable channels for down-dip migration of mete-

oric water to the base of carbonate units or even to the

regional base level. The movement of water along such

fracture zones was the major cause for the formation of

extensive underground cavern systems, which later become

sites of ‘tiankeng’ development (e.g. Klimchouk 2006;

Fig. 3c, e, f).

The last important structural feature that governs the

morphology of karstic terrains in northeastern Vietnam is

the interaction of all types of overprinting structures that

appear in carbonate units in a certain area. The develop-

ment of late, brittle, non-penetrative structural fabrics such

as joints, fractures and cleavage, not only produces zones

of high permeability within the carbonate units, but also

reactivates and modifies pre-existing structures formed

either during the formation of the rock units or by earlier

deformational events. Within the karstified terrains in

northeastern Vietnam, sink holes and underground channel

systems are commonly not restricted to, or preferably

developed along, any one structural system but occur at the

intersections between different types of regional structures

that penetrate deep into the lower parts of the carbonate

units. Such structural systems can create region-wide

underground channel systems down to base level that may

be more than thousand meters from the high mountain

peaks (e.g., Figs. 6b, d, 8; Vu Thanh Tam et al. 2009).

Finally, neotectonic regional unroofing of cavern sys-

tems in tropical conditions may play an important role in

the collapse of the karst systems and lead to the formation

of typical cone and tower karst morphology characterized

by large depressions, gorges, and valleys, saddles, hills,

caves, fengcong and fenglin structures (e.g. Klimchouk

2006) that form dominant karstic morphological features of

Vietnam (Figs. 3, 4, 5).

Conclusions

Analysis of the geological structural pattern and its rela-

tionship to the karstified assemblages in northeastern

Vietnam reveals that a complex regional structural frame-

work produced during a multiphase deformational history

during the formation and consolidation of the southeastern

portion of Asia continent played an important role in the

present-day occurrence, geometry and geomorphology of

the carbonate successions and the resultant unique karstic

Fig. 7 a A cavern system developed along the intersection between

sedimentary layering (gently dipping from right to left) and brittle

fracture system (steeply dipping in the left side of the photo)

northwest of Meo Vac Town, Ha Giang province. b Groundwater

discharges along a zone of brecciation developed within a brecciated

zone in massive Carboniferous-Permian limestone in Ta Lung

commune, Ha Giang province. The intense spaced fragmentation of

the rocks had produced abundant of pore-space within the breccia

zone, which has become a favorable environment for groundwater

localization

Environ Earth Sci

123

landscapes in northeastern Vietnam. The tectonic move-

ments during early stages of regional deformation gener-

ated extensive thrusting and associated folding, which led

to the tilting, fracturing, over-thickening, or dismember-

ment of the carbonate successions along high-strain zones

in ductile to brittle environments. In contrast, the over-

printing of the late brittle structures, in the form of non-

penetrative, highly fractured zones on older structures

resulted in the local augmentation of porosity within the

carbonate units. The combination of all structural elements

in the carbonate units, combined with the primary sedi-

mentary structures, is therefore is the most important

control on local and regional hydrological systems,

resulting in unique karst morphology. All types of struc-

tures contribute to the tilting, thickening and repetition or

displacement of the karstified units, whereas the cross-

cutting structures improve the porosity of the rocks as well

as form channel systems that enhance significantly the

infiltration, migration and/or localization of groundwater in

the carbonate units and led to the regional extensive

development of karst systems before they are shaped by the

modern exogenic processes

Thus, regional tectonic structures are important con-

trolling factors in the spatial occurrence of the carbonate

units, the behavior of hydrogeological systems, the present

geometry, landscape, as well as and natural hazards of the

karstified terrains in northeastern Vietnam. Proper identi-

fication of all types of structures within karstified units

therefore important and must be properly addressed in any

geological study of the karst areas, especially in assessment

of water resource and natural hazards.

Acknowledgments This work was partly supported by Vietnam’s

National Foundation for Science and Technology Development

(NAFOSTED), Project No. 105.06.70.09 and National Program on

Science and Technology for National Disasters Prevention, Envi-

ronmental Protection and Rational Utilization of Natural Resources of

Vietnam (KC-08/06-10). We are grateful to Dr. James LaMoreaux

and Dr. Jacqueline Halpin for their thoughtful reviewing and com-

ments that significant improved the quality of the manuscript.

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map of Pa Vi area, Meo Vac

district, Ha Giang province,

showing a typical example of

the interrelationship between

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b Rose diagram showing the

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image analysis

Environ Earth Sci

123

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