䈖䈉䈋䈇䊐䉤䊷䊤䊛╙ 㪈㪈 ภ㩷 㪆㩷㪉㪇㪇㪊㪅㪈㩷Landslide Risk Evaluation in the Machu Picchu World Heritage,
Cusco, Peru
Kyoji SASSA*1, Hiroshi FUKUOKA*1, Haruo SHUZUI*2, Minoru HOSHINO*3*1

Disaster Prevention Research Institute, Kyoto University, Kyoto, Japan
Osaka Office, Nihon Koei Co. Ltd., Osaka, Japan*3
Geographical Survey Institute, Tsukuba, Japan.
Keywords: Risk evaluation, Prediction, Monitoring, Precursor stage of landslide*2

1. INTRODUCTION
1.1 Background and Short History
This paper aims to supplement the theme talk in the Panel Discussion “Machu
Picchu World Heritage at Landslide Risk” during the International Symposium on
Landslide Risk Mitigation and Protection of Cultural and Natural Heritage.
Prediction or identification of precursor phenomena of large scale landslides is
not an easy task. Large-scale landslides do not occur in the same place in a short
return period compatible to life period of human beings. It is a kind of geologicalprocess and the return period of large-scale landslides are usually very long in theorder of thousand years or tens of thousand years or even longer.
Before the Hyogoken-Nanbu earthquake took place, most of the Japanesepeople regarded that earthquakes occurring in the order of thousand years wasalmost out of scope in present planning of disaster prevention measures. However,such earthquake caused great damages to mega city area of Kobe. So now it isclearly understood that even infrequent phenomena such as movement of active
faults and earthquakes should be seriously considered and people prepared for that.
Frequency of active faults and large-scale landslides are rather similar, though thecasual forces of phenomena are different; faults by crustal horizontal stress,
landslides by gravitational vertical stress.
Protection of mega city from earthquakes is very important, and we,researchers involved in the field of disaster prevention should focus our study
toward a more reliable prediction of site and time. Though the disaster caused bylandslides are not so great in the number of death comparing to earthquakes, theMayuyama landslide in Unzen, Japan, 1792 killed 15,000 people (Sassa 1999) andthe most recent Las Colinas landslide killed around 600 people in El Salvador in
2001. So landslides cause not a little disaster.
Entering 21st century, we are more and more aware of the value of theenvironment, especially regarding the invaluable cultural and natural heritage.
Those are very fragile treasure for humanity, which cannot be rebuilt once they
were destroyed. People worked for economic development in the last century, andthe industrial progress and economic development is still very important for thebase of society, but at the same time, we have notice that we should protect andleave our invaluable treasures of humanity to the next generation so long as
possible.
Fortunately the progress of geosciences is approaching to a level to identify
precursor phenomena of large-scale landslides, and assess the location, size,
velocity, and hazard area of these landslides. It was recognized during theInternational Decade for Natural Disaster Reduction to create less hazardous㪁㩷㪣㪅㪩㪅㪤㪅㩷㪸㫅㪻㩷㪧㫉㫆㫋㪼㪺㫋㫀㫆㫅㩷㫆㪽㩷㪚㫌㫃㫋㫌㫉㪸㫃㩷㪸㫅㪻㩷㪥㪸㫋㫌㫉㪸㫃㩷㪟㪼㫉㫀㫋㪸㪾㪼㪃㩷㪠㫅㫋㪼㫉㫅㪸㫋㫀㫆㫅㪸㫃㩷㪪㫐㫄㫇㫆㫊㫀㫌㫄㪃㩷 㩷 㪉㪇㪇㪉㪅㪈 ⻠Ṷ㓸䈎䉌䈱ォタ㩷㪋㪌㩷㪣㪸㫅㪻㫊㫃㫀㪻㪼㩷㪩㫀㫊㫂㩷㪜㫍㪸㫃㫌㪸㫋㫀㫆㫅㩷㫀㫅㩷㫋㪿㪼㩷㪤㪸㪺㪿㫌㩷㪧㫀㪺㪺㪿㫌㩷㪮㫆㫉㫃㪻㩷㪟㪼㫉㫀㫋㪸㪾㪼㪃㩷㪚㫌㫊㪺㫆㪃㩷㪧㪼㫉㫌㩷

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world in the last decade of 21st century. The landslide hazard assessment in Lishan(resort palace of Tang Dynasty), Xi’an, China by DPRI/KU and the Xi’an
Construction Committee was successful. The landslide risk assessment based on
the joint research has convinced the landslide risk to the Chinese government aswell as the Shaanxi Provincial Government and the Xi’an city. Based on thelandslide risk assessment research, landslide prevention works were initiatedbefore occurrence of any disaster due to landslides. Then, Prof. Edward
Derbyshire of the IGCP scientific committee invited DPRI/KU to propose aproject. IGCP-425 “Landslide Hazard Assessment and Cultural Heritage”. theproject was adopted and now on-going. The Machu Picchu landslide wasintroduced by Raul Carreno as a part of IGCP-425 sub-project “Study andprotection of Inca cultural heritage on landslide zone at Cusco, Peru”.
DPRI/KU team investigated Machu Picchu in March 2000 with support fromstaffs of INC and INRENA in Machu Picchu, and installed extensometers inNovember 2000, and reported those results in the UNESCO/IGCP Symposium on
Landslide Risk Mitigation and Protection of Cultural and Natural Heritage inTokyo, 2001. Those reports were introduced by Yomiuri Newspaper in Japan,“New Scientists” in UK, Civil Engineering by ASCE in USA and others. The
article by “New Scientists” was sensational, because of other articles in Yomiuri! and in Civil Engineering were published after the review by Sassa.
Newspaper
However, the New Scientist article was based only on telephone interview and notreviewed. The article was written with serious misunderstandings in some parts.
This article caused sensation over the world. Therefore, UNESCO thought thenecessity to inform a real state of investigation and published “Rumbles at Machu
Picchu” article in “World Heritage Review,” No.20, May 2001 (Bandarin 2001).
During the discussion within the UNESCO/IGCP symposium in Tokyo,
participants agreed to establish a new International Consortium on Landslides(ICL) to promote worldwide landslide research. The 2001 Tokyo Declaration
proposed the investigation and research on Machu Picchu at landslide risk as its
initial project of ICL. It is the result that all participants realized the greatsignificance of investigation of Machu Picchu from both aspects - Sciences andProtection of Cultural Heritage.
DPRI/KU and colleagues investigated Machu Picchu in October andNovember in 2001 with cooperation from INC and INRENA. Jiri Zbelebil and Vit
Vilimek of Czech group of IGCP-425 intended to join the field investigation withsupport from the Czech government. But the timing was a bit delayed, so joint
investigation was not conducted. However, their research is to be presented in thesame panel discussion. Those investigations from various aspects or teams will
present better view of Machu Picchu landslide risks.
1.2 Outline of Machu Picchu World Heritage
Inca’s world heritage is located northwest of Cusco, Peru (Fig.1). It was
declared a World Heritage of Humanity in terms of both cultural and naturalproperty by UNESCO in 1983. It is also an ecological sanctuary because of its
ecological richness. The present style of citadel was probably built by the Incas in
the 15th century. It remained untouched after the collapse of the Inca empire in
1540 through the colonial period because of its isolated location on the top of asteep mountain. Machu Picchu became known to the world after its “scientificdiscovery” by Prof. Hiram Bingham in July 1911. As time passed, it seemed that㪋㪍㩷䈖䈉䈋䈇䊐䉤䊷䊤䊛╙ 㪈㪈 ภ㩷 㪆㩷㪉㪇㪇㪊㪅㪈㩷

Machu Picchu citadel possibly has been affected by landslides. The photo shownin Fig.1 was taken by H. Shuzui (a member of the Japanese team). You may see abeautiful citadel is constructed on the top of rocky mountain. At the same time,
you may find this part of mountain ridge is different from other part of themountain ridge seen behind the citadel (Una Picchu and Huayna Picchu). The partcalled as Plaza in which the citadel was constructed has a flat area or an evenconcave area sandwiched by two ridges (Intiwatana in the left side peak in front of
Una Picchu and the residential building area in the right side peak). By the eye oflandslide researchers, the Plaza area seems to be re-profiled by filling earth ordebris to the cracks between two ridges along the dotted line. As shown in theprevious report (Sassa et al 2001), the dot line passed through a zone of broken
structure in the extension of right bottom of Fig.1. This hypothesis is not yet
proved by monitoring, drilling, geophysical exploration or direct excavation orother reliable methods. However, any phenomena to deny this hypothesis is not
yet found. Therefore, what is the cause of Plaza geomorphology, which isapparently different from other parts of mountain ridge in this Machu Picchu area,
should be investigated.

Huayna Picchu

Una Picchu

Fig. 1 Location and view of Machu Picchu Inca citadel on the mountain ridge,
Cusco, Peru.
Sassa et al presented a landslide distribution map based on chiefly air photo byGeographical Institute, Peru, 1963 and field investigation from a charteredhelicopter and walking in Fig.2. Landslide blocks were drawn on the
topographical map used in the report by K. Wright and R. Wright 1997. It is
included in Wright and Zengarra, 2000. The ridge connecting Mt. Machu Picchu㪋㪎㩷㪣㪸㫅㪻㫊㫃㫀㪻㪼㩷㪩㫀㫊㫂㩷㪜㫍㪸㫃㫌㪸㫋㫀㫆㫅㩷㫀㫅㩷㫋㪿㪼㩷㪤㪸㪺㪿㫌㩷㪧㫀㪺㪺㪿㫌㩷㪮㫆㫉㫃㪻㩷㪟㪼㫉㫀㫋㪸㪾㪼㪃㩷㪚㫌㫊㪺㫆㪃㩷㪧㪼㫉㫌㩷and Mt. Huayna Picchu separates the slope as a gentle slope where Hiram
Bingham Accessing Road is constructed, and a steep slope. We have called thegentle slope with the accessing road as Front Slope including Blocks 1, 2 and 3,
and the steep slope as Back Slope. In this map, No.1 and No.4, No.6 and No.7 arelandslides. No.2 is an area, which may develop to an actual landslide or alandslide at precursor stage. No.5 of Intiwatana area shows some phenomena ofground deformation around them (Sassa et al. 2001). The long-term stability ofthis area is questionable. No.3 was probably the bottom of previous landslides. All
landslide debris slid away there. At present the lower half of slope seemed to be
not active.

Fig. 2 Landslides and potential landslides around the Machu Picchu Citadel (Sassa
et al.2001)㪋㪏㩷䈖䈉䈋䈇䊐䉤䊷䊤䊛╙ 㪈㪈 ภ㩷 㪆㩷㪉㪇㪇㪊㪅㪈㩷

500 m

0
Mt. Machu Picchu
Urubamba
River

N
A2
M4

1’
Hotel

Inca Citadel

M1

B2

1

M2
a

C1

C2

1’

P4
P5

2
b

d

Mt. Intipunku

3

c

P3
A1
Machu-Picchu
Fault

M3

P2

Mt. Huayna
PicchuB1

UrubambaRiver

Huayna-Picchu
Fault

P1
Mt. Putukusi

Fig. 3 Working Map of Landslide Blocks 1, 2 and 3 in Front Slope(Our interpretation on landslides were written on the basic map of 1/5000
provided by UGM)
A1-A3, B1-B3, C1-C3: Lines for Sections for Block 1, Brock 2 and crosssections
ԘԙԚ: Blocks of landslides or potential landslides.
1’ : Expanding blocks of Block 1 to Block 2 and 3a, b, c, d: Sub-blocks of Block 2 which seem to move up towards the citadel
area from the border. (a: a retrogressive landslide, b : possible rocktopple, c: a recent landslide, d: shallow landslides which have not yet
slid so much.): Landslide debris at the toe of slope
M1-M5: Locations of extensometers
P1-P5: Photos of Block 2 from various directions㪋㪐㩷㪣㪸㫅㪻㫊㫃㫀㪻㪼㩷㪩㫀㫊㫂㩷㪜㫍㪸㫃㫌㪸㫋㫀㫆㫅㩷㫀㫅㩷㫋㪿㪼㩷㪤㪸㪺㪿㫌㩷㪧㫀㪺㪺㪿㫌㩷㪮㫆㫉㫃㪻㩷㪟㪼㫉㫀㫋㪸㪾㪼㪃㩷㪚㫌㫊㪺㫆㪃㩷㪧㪼㫉㫌㩷

2. FIELD INVESTIGATION OF LANDSLIDE RISK IN BLOCK NO.2
The authors investigated Machu Picchu area, especially Block No.2 during 24– 28 October 2001, and examined the site for a series of long span extensometers
including a span crossing Plaza in the citadel. Based on this investigation, and
1/5000 map we obtained this time from UGM (Machu Picchu Joint Managing
Unit), we modified Fig.2 and made another working map for Block No.1 andBlock No.2 as shown in Fig.3. Sites of most information which are referred laterin this paper were included in this map, as well.
The major findings during our investigation are explained using photos Photo
1- Photo 5 in Fig.4.
Photo 1 presents a view from the top of Mt. Putukusi toward Block (1), (1’)
and (2). The color version of this photo is presented in the color gravure. The
citadel is constructed on the mountain ridge, Intiwatana is located on its peak in
the point of arrow. Sharp cliffs made by landslides (rock slides and rock topples)seem to gradually move upward from the border between (1’) and (2) and the toeof slope to the citadel site. Four deep vertical cracks due to faults subdivided
Block 2 as you may find some of them in the toe of Block 2 in the photo,especially one crack is very big.
Photo 2 presents the frontal view of sub-landslide ( c ) from the opposite bank.
Easily supposed from the view, the landslide was not yet eroded and keep theoriginal form of landslide mass, and it is not old landslide (the date is not yet
confirmed). We set a central investigation line passing this landslide andIntiwatana. This is the most disturbed area of Block 2. Photo 3 presents a view
from the bridge to Block (1’) and the sub-block (a) of Block 2. You may findprevious landslide debris in front of the head scarp. A concave ground surface of
sub-block (a) is seen in front of the citadel, though it is not very clear in this photo.
It indicates gradual movement and monitoring by extensometers showed amovement though the records are still very limited.
Photo 4 and 5 were taken from the back side of citadel. The arrow A pointed ashear band, which is possibly a potential sliding surface of Block 2. A shear bandis gently dipping, and a shear displacement around the shear plane is observed,
and furthermore, rocks seem to be slightly dragged below the shear plane. Photo 5
is the close up photo of the shear band. This time we firstly walked around theback slope of Machu Picchu. Therefore, this finding is very important for theplanning of further investigation, though it is too early to conclude this shear band
(possibly gently dipping fault) as the potential sliding surface of Block 2.
However, this is the most likely candidate of the sliding surface at present. The
further investigation plan should include the examination of this shear band.
Figure 5 presents two photos taken from a chartered helicopter taken by Kyoji
SASSA in March 2000. These two photos gave us another view of this potential
sliding surface (arrow A). You will possibly find that this potential sliding surface
dips almost parallel to the front slope. The dot line made of round circle (yellow
color line in the gravue) points the shear band dipping to the front slope. The dotline made of square mark (red color line in the gravue) shows the possible
landslide border of Block 2 on the ground surface. You may notice a landslidedebris filling a part of the Urubamba River in the left photo. The landslide debris
is gradually flowed out, and such loss of toe support may trigger further landslide
as is the common process in many of landslides.

㪌㪇㩷䈖䈉䈋䈇䊐䉤䊷䊤䊛╙ 㪈㪈 ภ㩷 㪆㩷㪉㪇㪇㪊㪅㪈㩷

Fig. 4 Photos of Block 2 in the various directions (photo 1 – photo 5 as follows)

IntiwatanaԘԙԘPhoto 1 Block No.2 from Mt. Putukusi shooting (taken by H. Shuzui)

Photo 2 A recent landslide in the toe of Block 2 from the opposite bank㪌㪈㩷㪣㪸㫅㪻㫊㫃㫀㪻㪼㩷㪩㫀㫊㫂㩷㪜㫍㪸㫃㫌㪸㫋㫀㫆㫅㩷㫀㫅㩷㫋㪿㪼㩷㪤㪸㪺㪿㫌㩷㪧㫀㪺㪺㪿㫌㩷㪮㫆㫉㫃㪻㩷㪟㪼㫉㫀㫋㪸㪾㪼㪃㩷㪚㫌㫊㪺㫆㪃㩷㪧㪼㫉㫌㩷

Inca Citadel

a

b
1’

Photo 3 Landslides invading the side of Block 2

A

Photo 4 A shear band, possibly the potential sliding surface of Block 2 is visible
in the back slope (arrow A)㪌㪉㩷䈖䈉䈋䈇䊐䉤䊷䊤䊛╙ 㪈㪈 ภ㩷 㪆㩷㪉㪇㪇㪊㪅㪈㩷

Photo 5 A zoomed up photo of the potential sliding surface (shear displacement at
the shear band and toppling deformation below the shear band are visible)
taken by K. Sassa
3. INTERPRETATION OF POSSIBLE LANDSLIDE PROCESS
To get the general image, an air photo taken from a high altitude will be thebest solution. A stereo pair photos in Fig. 6 presents the location of Machu Picchu
citadel (a circled part) and its surroundings. The Urubamba River encircled the
Machu Picchu area along the strong fault system. You may find the front slope(Block No.1, 2 and 3 in Fig.3) of Machu Picchu seems to have been excavated byprevious mass movements. The mountain ridge of the part of citadel seems tohave been subjected to landslides, and partly removed. Mt. Putsukusi is not a partof landslide block. It is a stable rock mass as the whole, though surface rock slides
are observed. No great flow-mountain as a result of a big landslide is not seenalong the Urubamba River. Therefore, it will be supposed that landslides having
excavated the front slope were probably not a single gigantic landslide, but aseries of retrogressive landslides so as to be seen in Block 1 at present and in theborder of Block 2.
To assess the landslide risk, the process of landslides until the present stage
should be correctly understood by the field investigation and interpretation. But
the investigation is not enough to conclude the process. However, the draft
interpretation was presented in the previous symposium (Sassa et al 2001). Fig.7
shows the second draft of interpretation. The stages of landslide evolution were
illustrated for Block 1 and 2 in a schematic form. In the old time, probably
retrogressive landslides occurred in the front slope of Machu Picchu. (Somelandslides occurred in the back slopes, too. But Block 1 and 2 are examined in thispaper.) After the whole landslide debris moved out to the Urubamba River, thedownward erosion proceeded. The level of Urubamba River was shifted aroundone hundred meters downward almost to the present level. Three slopes of Block
1, 2, 3 showed the difference in the landslide evolution. The slope of Block 1 hadbeen most heavily subjected to toe erosion of the Urubamba River as easily

㪌㪊㩷

A

Fig. 5 Photos from a helicopter shooting the potential sliding surface (marked as A) and the potential borders of landslide on
the ground surface taken by K. Sassa

㪣㪸㫅㪻㫊㫃㫀㪻㪼㩷㪩㫀㫊㫂㩷㪜㫍㪸㫃㫌㪸㫋㫀㫆㫅㩷㫀㫅㩷㫋㪿㪼㩷㪤㪸㪺㪿㫌㩷㪧㫀㪺㪺㪿㫌㩷㪮㫆㫉㫃㪻㩷㪟㪼㫉㫀㫋㪸㪾㪼㪃㩷㪚㫌㫊㪺㫆㪃㩷㪧㪼㫉㫌㩷㪌㪋㩷

A䈖䈉䈋䈇䊐䉤䊷䊤䊛╙ 㪈㪈 ภ㩷 㪆㩷㪉㪇㪇㪊㪅㪈㩷

Mt.
Putukusi
Mt.Putukusi
Putukusi
Mt.

Fig. 6 Airphoto of Machu Picchu (Geographical Institute, Peru)
Block No.1 (H. Bingham Road)

Block No. 2 (Inca citadel)

Old (Stage 1)

Old (Stage 1)

Downward
ErosionDownward
ErosionIntermediate(Stage 2)

Present (Stage 2)
Machu Picchu
CitadelRidgesPresent (Stage 3)
e
slid
nd
La toeat
Landslide Debris

Mt. Huayna Picchu

Block 3Block 2Block 1

Fig. 7 Hypothesis of landslide process in Machu Picchu㪌㪌㩷㪣㪸㫅㪻㫊㫃㫀㪻㪼㩷㪩㫀㫊㫂㩷㪜㫍㪸㫃㫌㪸㫋㫀㫆㫅㩷㫀㫅㩷㫋㪿㪼㩷㪤㪸㪺㪿㫌㩷㪧㫀㪺㪺㪿㫌㩷㪮㫆㫉㫃㪻㩷㪟㪼㫉㫀㫋㪸㪾㪼㪃㩷㪚㫌㫊㪺㫆㪃㩷㪧㪼㫉㫌㩷supposed by the curved path of the river and flow direction in Fig.3. Firstly theslope started to slide as illustrated in the intermediate period (Stage 2) of Block 1.
The initial landslide retrogressively expanded to the upper slope and toward theside slopes, then the present situation of Stage 3 where active landslide debris
covers the slope was formed. You may find in Fig.3 that the Urubamba River was
pushed forward by the landslide debris provided by Block 1. So this landslidedebris has probably worked for the protection of toe erosion of Block 2. Becauseof this protection, the evolution of Block 2 was probably much delayed and it isstill in the Stage 2. The most delayed block in slope evolution is Block 3. Afterprevious landslide debris moved out, no major landslides occurred because there
is almost no river erosion as imagined from Fig.3. The landslide evolution in the
cross section is illustrated in the right bottom of Fig.7. Only Block 1 was
subjected to major landslides at the present level of Urubamba River and locatedin the lower elevation which continues to the around present level of the river bed.
And Block 2 is now following the process of Block 1. Fig.8 shows thelongitudinal section along A1-A2-A3 in Block 1. The depth of landslides is notknown, but the whole slope from the mountain ridge to the river is affected by
active landslides and covered by landslide debris. Fig.9 presents the longitudinal
section along B1-B2-B3 in Block 2. The section B1-B2 shows the active landslide
at the toe (c in Fig.3), and others are possibly at the precursor stage. The potential
sliding surface will be a shear band found in Fig.4 and Fig.5. If we consider thatthe potential sliding surface is located in the level as shown in Fig.9, the depth oflandslide is around 100-150 m.
Figure 10 presents the cross section along C1-C2-C3. The potential sliding
surface seems to be inclined similar to the ground surface, as shown in photos in
Fig.4 and Fig.5 and the plot of the shear band in the topographical map suggests.
In this figure, the sliding surfaces of real landslides are drawn by a real line
though the depth is not yet confirmed. The sliding surfaces of potential or
precursor stage of landslides are drawn by a dot line.
There is a Question for the reason why the sliding surface goes up to the Plazain Block 2 (Fig.1, 3, 5, and 9), which may split Plaza of Inca Citadel. The reason
is interpreted below from the data obtained up to now:
The ground water will increase in the lower part of the slope collecting groundwater from the upper slope because the shear band is probably having a low
permeability and dipping parallel with the front slope. As shown in the crosssection C1-C2-C3 in Fig.10, the shear band is gently dipping to the
Huayna-Picchu fault side. It means that ground water flows from Block 1 or 1’ toBlock 2. Therefore, probably the ground water level and pore water is greater inthe lower part of Block 2, and almost no ground water near the top of slope. In
this case, the top of Block 2 (area of Plaza and Intiwatana) is rather stable, so
tensile stress should act in this zone. Accordingly tension cracks may be formed.
The concavity in the Plaza likely corresponds to the tension crack, though theconcavity was filled possibly by Inca’s people for flatter ground suitable for theirliving, which is not clearly visible on the ground surface at present.

㪌㪍㩷䈖䈉䈋䈇䊐䉤䊷䊤䊛╙ 㪈㪈 ภ㩷 㪆㩷㪉㪇㪇㪊㪅㪈㩷

2800
A2

Elevation (m)

2600

2400

2200

2000

Urubamba
River
A1

A3

1800
0

400

800
1200
Horizontal Distance (m)

1600

2000

Fig. 8 Longitudinal section (A1-A2-A3) of Block 1
2600
Plaza
B2
Intiwatana

Elevation (m)

2400

les

2200
Urubamba
River
2000

W
G.

B1

at

s

er
Urubamba
River

h
ric

B3
1800
0

400

800
Horizontal Distance (m)

1200

1600

Fig. 9 Longitudinal section (B1-B2-B3) of Block 2
2800

S.A. Intipunku

Mt. Huayna
PicchuC1

Elevation (m)

2600

C3

Previous landslides (Block 1’ )A block b atlandslide risk

2400

Shallowlandslide d

C2
2200

Macchu - Picchu
Fault
2000
0

400

Block No.1

Huayna - Picchu
Fault

Block No.2
at landslide risk

800
1200
Horizontal Distance (m)

1600

2000

Fig. 10 Cross section (C1-C2-C3) of the front slope of Machu Picchu㪌㪎㩷㪣㪸㫅㪻㫊㫃㫀㪻㪼㩷㪩㫀㫊㫂㩷㪜㫍㪸㫃㫌㪸㫋㫀㫆㫅㩷㫀㫅㩷㫋㪿㪼㩷㪤㪸㪺㪿㫌㩷㪧㫀㪺㪺㪿㫌㩷㪮㫆㫉㫃㪻㩷㪟㪼㫉㫀㫋㪸㪾㪼㪃㩷㪚㫌㫊㪺㫆㪃㩷㪧㪼㫉㫌㩷

Fig. 11 Two types of extensometers

Ex

Ex

te

ns

e
om

te

te

om
ns

e te

rC

Stable
Rock

r B

ԙ
Exte

nsom

eter

A

Ԙ

Ԙԙ: Landslide Blocks

StableGroundFig. 12 Illustration of the concept of extensometers
4. MONITORING OF EXTENSOMETERS IN MACHU PICCHU
To evaluate landslide risk, monitoring of the ground deformation, thegeological drilling, monitoring of shear displacement and ground water level
and/or pore water pressure inside drill holes are vitally important and necessary.
Without such investigation, neither landslide risk, nor the safety of slope can bereliably evaluated in the convincing way. Without such reliable landslide risk
evaluation, neither effective landslide remedial works can be planned, nor highcosts of remedial works can be approved.
As the first step of quantitative investigation, two types of simple
extensometers were installed in the Machu Picchu slope. One is a handmade
manual reading extensometers as shown in the left photo of Fig.11. Using a pulley
and a super invar wire (a special kind of metal with least influence of temperature),
movement of the distance between two points is mechanically enlarged by 5 times
and indicated on the dial with a pointer. Another type is theoretically the same,㪌㪏㩷䈖䈉䈋䈇䊐䉤䊷䊤䊛╙ 㪈㪈 ภ㩷 㪆㩷㪉㪇㪇㪊㪅㪈㩷

movement was also mechanically enlarged by 5 times, and it is recorded on arecording paper continually. The recording drum is rotated by landslide movement,
while the recording pen shifts in a steady speed by a dry battery from the left tothe right as shown in the right photo of Fig.11.
The concept of extensometer is illustrated in Fig. 12. The height of poles forextensometers is different on the length of span of two poles. When monitoring by
a long span, high poles are used to pass the super invar wire over trees and roads,
and to avoid possible disturbance by animals and persons. While in the case ofmonitoring in a short span (which is usual case), low poles are used and the super
invar wire is protected by a pipe as shown in Fig.11. Extensometers have merits,
which are not affected by moisture, density or atmospheric pressure in the air andcause less trouble and very reliable because of very simple mechanical recording
system. They are different from sophisticated monitoring systems such as EDM(electronic distance meter) and GPS (global positioning system).

5ȀȀExtension (m m )10

Com pression

χ0ω

S1: Near Hotel "Sanctuary Lodge"
in Block No. 1-5

Compression •@ͺȀȀExtensio n (m m )

30

20

10

χ
ω 0

-10

-20



㪌㪐㩷

㪣㪸㫅㪻㫊㫃㫀㪻㪼㩷㪩㫀㫊㫂㩷㪜㫍㪸㫃㫌㪸㫋㫀㫆㫅㩷㫀㫅㩷㫋㪿㪼㩷㪤㪸㪺㪿㫌㩷㪧㫀㪺㪺㪿㫌㩷㪮㫆㫉㫃㪻㩷㪟㪼㫉㫀㫋㪸㪾㪼㪃㩷㪚㫌㫊㪺㫆㪃㩷㪧㪼㫉㫌㩷25

N2: Sub-Block (a) in Block No. 2

ͺȀȀ Extension (m m )

20
15
10

Com pression

χ
ω

5
0
-5

-10
Nov. 1
2000

Jan. 1
2001

March 1
2001

May 1
2001

Sept. 1
2001

July 1
2001

Nov. 1
2001

DateFig. 14 Records of extensometer (N2 ) in the monitoring site (M2) in Sub-Block(a) in Block 2ͺȀȀExtension (m m )15

Com pression

χωBack Slope of Intiwatana
10no data

50
no data-5

no data

N5
N6

-10

N7
N8

-15
Nov. 1
2000

Jan. 1
2001

March 1
2001

May 1
2001

July 12001

Sept. 1
2001

Nov. 1
2001

DateFig. 15 Records of extensometers (N5,N6,N7,N8) in the monitoring site(M3) inthe back slope of Intiwatana
A series of extensometer installation from the stable ground to the stableground is most desirable to detect landslide blocks. The system is used in Lishan,
China (Sassa et al. 2001), and Zentoku, Japan. However, the easiest way to checkthe existence of movement is to set an extensometer crossing a head scarp to㪍㪇㩷䈖䈉䈋䈇䊐䉤䊷䊤䊛╙ 㪈㪈 ภ㩷 㪆㩷㪉㪇㪇㪊㪅㪈㩷

monitor the landslide movement. 12 extensometers were installed in five sites(M1-M5) as shown in Fig. 3. Fig. 13 presents the monitoring results of M1 near
the hotel Sanctuary Lodge in Block 1. The extensometer S1 showed gradualextension over a long term, while N1 showed compression after extension from
Nov.1 2000 to Nov. 2001. Movement of N1 is rather great. N1 is the manual
recording type, and S1 is the paper recording type.
Movement of both extension and compression in the same extensometer isinterpreted using Fig.12. When a single extensometer is installed as extensometer
B in the figure, extension means the movement of sliding block 1, andcompression means the movement of sliding block 2. Movement of sliding block1 decreases the support of sliding block 2 when two blocks are interconnected.
Probably extensometer records of N1, and S1 detect the movement of some ofsub-block in Block 1.
Figure14 presents the monitoring of N2 installed in the border of sub-block (a)of Block 2. The movement is rather great in the order of 10 mm. Fig.15 presents
the monitoring results of four extensometers installed in the steps (terraces) for
farming in the back slope of Intiwatana. In this part, a debris flow occurred
probably in 1999 or 2000 and the fresh trace of debris flow was observed from achartered helicopter in March 2000. These extensometers are planned to detect thepossible retrogressive landslides near the source area of the debris flow. Therefore,
those extensometers were not aimed to detect a deep seated landslide, but shallow
surface landslides. Those do not affect the Inca’s citadel, but it is good exercise tomonitor the ground surface movement, and good to totally check the precision,
reliability and problems of monitoring.
Figures13-15 present monitoring records of the short span extensometers, andnot a series of extensometers as shown in Fig.12. Therefore, the landslide size is
not estimated only by those data. However, comparing those data, the recorded
movement of S1 shows a gradual movement from January to the early April,though almost extensometers presented the termination of major movement before
early March. The movement detected by S1 is probably due to a deep seatedlandslide. It must be checked by further monitoring.
5. FURTHER LANDSLIDE INVESTIGATIONThe results of field investigation and monitoring suggest the possibility oflandslides, which possibly affect the Inca’s citadel. The exact understanding ofslope conditions and landslide risk evaluation need further investigation. Fig.16
illustrates a monitoring system to be employed in Block 2. A series ofextensometers from the Intiwatana (top of the slope) to the opposite bank of
Urubamba river is desirable to assess the location and size of landslide and its
danger reaching to failure. Monitoring result by a single method is better to be
examined by other methods. EDM and GPS methods are appropriate to be applied.
GPS has a merit of movement monitoring in wider area because their sets can beinstalled over the Block 2. EDM has a merit of very long span of monitoring,
though both are affected by atmospheric conditions. However, combination of
those methods and their integrated interpretation should present reliable results.
Drilling and the borehole inclinometer or alternative methods to detect the sliding
surface are very necessary to know the depth of landslide. Ground water
monitoring is necessary to evaluate the effect of ground water on this landslide.

㪍㪈㩷㪣㪸㫅㪻㫊㫃㫀㪻㪼㩷㪩㫀㫊㫂㩷㪜㫍㪸㫃㫌㪸㫋㫀㫆㫅㩷㫀㫅㩷㫋㪿㪼㩷㪤㪸㪺㪿㫌㩷㪧㫀㪺㪺㪿㫌㩷㪮㫆㫉㫃㪻㩷㪟㪼㫉㫀㫋㪸㪾㪼㪃㩷㪚㫌㫊㪺㫆㪃㩷㪧㪼㫉㫌㩷

2600

GPS / EDM

GPS / EDM target

Intiwatana

Elevation (m)

2400

GP

2200

2000

G

/
PS

ED

E
S/

DM

0

ets

M

B1
Urubamba River
1800
-200

rg
Ta

200

Borehole Inclinometer andground water monitoring

400
600
Horizontal Distance (m)

800

1000

1200

Fig. 16 Illustration of monitoring system for the precise understanding of potential
landslides

Intiwatana

Planned Superinvar Wire location
Residential area

Fig. 17 Photo of a planned super invar wire location crossing the Plaza.

From the field observation, ground water flowing along the shear band withrelatively less permeability from the top to the toe and possibly from the Block 1
side to the Huayna-Picchu fault side must be a major causal factor of thislandslide. This means that drainage will be effective to stabilize this landslide.
The prevention of toe landslides must be very effective in order to prevent further
retrogressive landslides.

㪍㪉㩷䈖䈉䈋䈇䊐䉤䊷䊤䊛╙ 㪈㪈 ภ㩷 㪆㩷㪉㪇㪇㪊㪅㪈㩷

Finally the photo of the first long span extensometer to be installed crossing
Plaza is shown in Fig.17. With cooperation from engineers of INC and INRENA,
our team examined the site for a long span extensometer and conducted a trial
installation, though the super invar wire and a long span extensometer were notyet installed. However, we have checked that such installation is possible withalmost no disturbance of scenery of Plaza under the examination of thearchaeologists working for the Machu Picchu World Heritage. A super invar wireis 1.0 mm in diameter though the line was drawn in a visible way in Fig.17, and it
is passing high above the walking visitors.
6. CONCLUSION
The results of investigation by the Japanese team conducted in October 2001
was introduced. We could walk around the Machu Picchu slope in addition to theexamination of sites for the installation of long span extensometers. Major
findings of this investigation are;
1) Retrogressive landslides have probably proceeded in the past and are stillon-going in the Machu Picchu slope. The progress of landslide evolution stage
is different in Block 1, 2, 3. Present stages of each block are informative forthe assessment for the future process of landslide activities.
2) A relatively new landslide at the toe of Block 2, on which the Inca citadel isconstructed, was observed though the exact date is not yet known. A shear
band, possibly a potential sliding surface of Block 2 was found. It is gently
dipping to the front slope, and also gently dipping toward the Huayna Picchu
Fault.
3) Ground water is likely to flow downward and also toward the Huayana Picchu
Fault direction possibly along the shear band with a relatively low
permeability. The ground water must be poor in the top of Block 2 and rich in
the lower slope. It may be the cause of possible head scarp splitting Plaza.
4) If ground water along the shear band and the retrogressive landslides in theborder between blocks (1’) and (2) and also in the toe cliff will be majorcausal factors of Block 2, reduction of those causal factors must be effective
landslide remedial measures.
5) Reliable understanding of the present state and process of landslides can not
be obtained without reliable monitoring of deformation on the ground surface,geological drillings and preferably geophysical exploration, monitoring of theshear displacement and ground water level and/or pore pressure inside theboreholes. However, we may conclude that there is a necessity of further
investigation to evaluate landslide risk in Machu Picchu in order to avoid or
postpone its possible failure at least.
ACKNOWLEDGEMENTThe Japanese investigation team was well received by the related agencies in
Peru and obtained significant support and cooperation. We acknowledge thefollowing institutes and persons for their cooperation to this investigation: Mr.
Edwin Benavente Garcia, Departamental Director of Cusco office of the Instituto
National de Cultura (INC) and his staffs, engineers of Machu Picchu office ofInstituto National de Recursos Naturales (INRENA). Prof. Mutsumi Ishitsuka,
Director of the Ancon Observatory, Instituto Geofisico del Peru (IGP) has
cooperated from the beginning of this Machu Picchu investigation in all aspects.

㪍㪊㩷㪣㪸㫅㪻㫊㫃㫀㪻㪼㩷㪩㫀㫊㫂㩷㪜㫍㪸㫃㫌㪸㫋㫀㫆㫅㩷㫀㫅㩷㫋㪿㪼㩷㪤㪸㪺㪿㫌㩷㪧㫀㪺㪺㪿㫌㩷㪮㫆㫉㫃㪻㩷㪟㪼㫉㫀㫋㪸㪾㪼㪃㩷㪚㫌㫊㪺㫆㪃㩷㪧㪼㫉㫌㩷

Dr. Raul Carreno of Cusco, a deputy leader of IGCP-425, has cooperated throughthe whole investigation, and supported our activities. All of them are deeply
appreciated for their kind cooperation. Finally all colleagues of Landslide Sectionof the Disaster Prevention Research Institute, Kyoto University are acknowledged
for their cooperation to analyze and to present the results of field investigation andmonitoring.
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Carreno, R. and Bonnard, C.1997. Rock slide at Machupicchu, Peru. LandslideNews, No.10, pp.15-17.
Hadfield, P. 2001. Slip sliding away. New Scientists, Reed Business Information,
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Wright, K.R. and A.V. Zengarra. 2000. Machu Picchu – A Civil Engineering
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㪍㪋㩷