eca

SXG390 ECA David Freeman PI R8262201

CONTENTSSection Title Page

Abstract 21 Introduction 31.1 Objectives 31.2 Methodology 32 Definition 43 What are lahars? 43.1 How lahars are triggered 44 Nevado del Ruiz; Location and Physiographic 54.1 Historical data 64.2 Chronology of the November 13th 1985 eruption and lahars 64.3 The November 13th 1985 lahars 84.4 The effects of the November 13th 1985 lahars 95 What was in place before the eruption? 105.1 International help 105.2 Monitoring and results of monitoring 105.3 The Hazard Map 115.4 Local Government versus National Government 136 What could have been done today? 156.1 Public education 156.2 Seismic surveillance, and Acoustic flow monitoring 156.3 Sabo check dams 167 Conclusions 188 References 20

List of FiguresFigure Title Page4.1 A Map of the area around Nevado del Ruiz, and mud flow deposits 64.2 A Chart of the volcanic explosivity index 74.3 Aerial view of Armero November 14th 1985 95.1 Preliminary map of volcanic hazards of Nevado Del Ruiz 115.2 Map of potential volcanic hazards of Nevado Del Ruiz volcano 125.3 Simplified management system and communication links November 13th 146.1 Diagram showing how sabo check dams work 176.2 A tubular grid sabo check dam 17

List of TablesTable Title Page

1 Summary of volumes of melt waters for the five main channels producing lahars

8

of 21


ABSTRACT

On November 13th 1985, a relatively small eruption of the stratovolcano Nevado del Ruiz in

Colombia, triggered several lahars, which swept down the valleys of the volcano, and travelled

more than 100km, engulfing the town of Armero. More than 23,000 people were killed and the

town was almost totally destroyed. How did such a comparatively small eruption, (a 3 on the

volcanic explosivity index (VEI)), trigger lahars resulting in such a great loss of life and destruction

of property, and infrastructure? Could anything have been done prior to this eruption to mitigate its

effect. It was known that the volcano was active, it had erupted earlier that year, and had produced

lahars in the past. Both the eruptions of 1595 and 1846 had produced lahars, which reached the area

on which Armero was built; and in both cases lives were lost. Was this a case of nature conspiring

against man, or was human error the main reason that so many people were affected by this

eruption and the subsequent lahars it triggered.

In the twenty years since the eruption of Nevado del Ruiz, what has been learnt by scientists and

politicians? What could be put in place today, either physically such as sabo check dams, or

systemwise like acoustic flow monitoring, to prevent such a disaster happening again, either in

Colombia or elsewhere in the world, where there exists a hazard of volcanic eruptions, which could

result in life threatening lahars.

of 21


1. Introduction

This report is about lahars, what they are, how they are triggered, why they can be so destructive,

and what their effects can be and how these effects can be mitigated. It focuses on one major lahar

event, the November 13th 1985 lahars following the relatively small eruption of Nevado del Ruiz

stratovolcano in Colombia, South America. The report will examine why this particular eruption

produced a lahar event of such destructive magnitude. It will examine the defences that were in

place to mitigate the effects of the eruption, and discuss what measures could be in place if the

event had happened today.

1.1 Objectives

The objectives for this report are fourfold.

1 To describe the nature of lahars, their different types and how they are triggered.

2 To outline the circumstances of the November 13th eruption and subsequent lahars. Why did the

town of Armero suffer such destruction, resulting in such a great loss of life. Was it the structure of

the volcano itself, or the size of the eruption, which caused the devastating lahars. Were the people

of Armero unaware of the risks of living under a volcano, or did they believe that they lived far

enough away from it, to be safe from the effects of an eruption.

3 This report will also evaluate any strategies in place at the time, designed to mitigate the risks of

loss of life, and destruction of property which Nevado del Ruiz posed. Why they failed, were the

people living in and around Armero just unlucky, or was there a large degree of human error

involved in this disaster.

4 Finally the report will discuss what has been learnt from this and other lahars, in the fields of

prediction and hazard management. What technologies, and strategies are available to scientist and

politicians today, 20 years later. How these can be used to reduce the risks of loss of life and

destruction of property posed by future lahars.

1.2 Methodology

As this is a literature based report I have, searched various databases to identify papers discussing

lahars, and the November 13th 1985, Nevado del Ruiz in particular. I have also researched papers

about other lahars, lahar predictions, and geohazard management. I found over 70 papers covering

these topics, of which about 70% I downloaded, printed and scan read. Of these I prioritised the

papers which, in my opinion best matched my objectives for the report, and read those first. This

report is the result of this research.

of 21


2. Definition

As part of the International Year of Planet Earth, 2008, the organisation Earth Sciences For Society

has defined a geohazard as “a term that includes geological hazards, like landslides and volcanoes,

hydrometeorological hazards like floods and freak tides, and geophysical hazards like earthquakes.

Any Earth process that poses risk to human life”[1]. Lahars are both hydrometeorological, and

geophysical, and if the volcano is situated in a populated area, they do pose a risk to human life.

3. What are lahars?

Lahar is an Indonesian term that describes a mixture of water and rock fragments flowing down the

slopes of a volcano and (or) river valleys. This term can and is used to cover various other terms

such as debris flows, hyperconcentrated flows, and volcanic mudflows. A definition of the term

lahar, was proposed in the late 1980’s at a Geological Society of America Penrose Conference [2]

"...lahar: a general term for a rapidly flowing mixture of rock debris and water (other than normal

streamflow) from a volcano. A lahar is an event; it can refer to one or more discrete processes but

does not refer to a deposit." This definition covers the transient nature of lahars. A typical lahar has

a water to sediment ratio of 40:60 by volume [3] The ratio of water to rock and sediment often

change during their flow. These changes occur because rock and sediment may be entrained from

the valley in which the lahar flows or the water volume maybe increased by rain or ground water on

the course of the lahar, this is termed “bulking” [4].

Lahars come in two flavours, hot and cold. Hot lahars involve water and hot volcanic debris; these

usually occur during or very shortly after a volcanic eruption. A cold lahar usually occurs some

time after an eruption, when the volcanic debris are cold.

When moving, a lahar looks like a mass of wet concrete, and carries rock debris ranging in size

from clay to boulders more than 10 m in diameter. Lahars vary in size and speed. Small lahars less

than a few metres wide and several cm deep may flow at few ms -1. Large lahars hundreds of metres

wide and tens of metres deep can flow at several tens of ms-1. Stratovolcanoes are the commonest

sites for lahars, due to the steep sided nature of stratovolcanoes, and the steep sided valleys which

usually form on them.

of 21


3.1 How are lahars triggered.

Hot lahars can be triggered in several different ways. The three main methods of producing lahars

are, ice cap melting, crater lake breaches, and heavy rainfall. These triggers can also combine to

cause lahars.

3.1.1. Ice Cap Melting

Hot ejecta can melt an ice cap at the top of the erupting volcano, this can trigger a lahar as in the

case of the 1985 Nevado del Ruiz lahar. The eruption materials need to be mechanically mixed with

snow and ice from the ice cap for enough melt water to be produced to trigger a lahar[4]. This can

be achieved by the ice cap being cracked by local earthquakes; which usually accompany any

eruption, and by different pulses of ejecta, melting a series of fissures. It is the size of the surface

area at which the ice and hot ejecta mix, that will determine the volume of melt water produced,

and not solely the volume of ice or snow.

3.1.2 Crater Lake Breach.

A lake crater can be breached, and the water mix with a pyroclastic flow to form a lahar. This is a

common trigger for many small lahars, as crater lakes, do not usually contain the volume of water

required to cause large lahars.

3.1.3 Heavy Rain Fall.

Heavy rainfall during an eruption can supply the water to form the lahar, as was the case at

Pinatubo in June 1991[5], as meteoric water from typhoon Yunya mixed with pyroclastic-flow

deposits and triggered several lahars.

3.1.4. Cold Lahars

Cold lahars can be triggered by lake crater breaches or heavy rainfall mixing with ash or volcanic

debris, which has settled in and around stream and riverbeds, on the sides of volcanoes.

Sudden landslides can also cause lahars, as in the case of the 1998 lahar at Casita volcano,

Nicaragua, when heavy rainfall from hurricane Mitch caused a catastrophic landslide on the side of

the volcano, triggering a lahar, resulting in 2500 fatalities.[6]

of 21


4. Nevado del Ruiz; Location and Physiographic

Nevado del Ruiz is a stratovolcano, part of the Andes chain of mountains, situated in the Cordillera

Central of Colombia at 4.88oN and 75.33oW, 100km west of the capital Bogotá. It is the northern

most volcano in Colombia, and the highest, with a summit elevation of 5,400m. It has a wide flat

summit, covered with 25 km2 of ice and snow. The crater, Arenas (which was the vent for the

November 1985 eruption), is situated to the north-eastern edge of the ice-cap. Prior to November

1985, there were many steep sided gullies and valleys, cut into the volcano on all sides. Nevado del

Ruiz is the source for many rivers in the area, including the Azufrado, Gualí and Lagunillas.[4]

Situated at the bottom of Nevado del Ruiz and 32km east of it, lies the town of Armero, with a

population of 35,000 (see Figure 4.1)

Figure 4.1 A Map of the area around Nevado del Ruiz , showing the pyroclastic and mud flow

deposits of November 13 th 1985 Eruption[7]

4.1 Historical data

There is historical data that tells of previous lahars in the area of Armero. In both 1595 and 1845

fatalities were recorded, with around 1000 killed by the February 19 th 1845 lahar, and 636 of the

native Gualí Indians died in the March 12th 1595 lahar, both events had killed about 70% of the

population of the Armero area [8,9]. More recently the 1935 and 1950 torrential rains have

produced mudflows that passed through Armero, causing serious damage. This last event would

have been within living memory of some of the inhabitants of Armero.[10]

of 21


4.2 Chronology of the November 13th 1985 eruption and the lahars

September the 11th 1985, an eruption event occurs, which triggers a moderate-sized lahar. It begins

at 6:30 p.m. and travels 27 km down the Rio Azufrado valley with a velocity of 2.8-8.5 ms-1

Late September - explosive phreatic activity continues, and strong ash emission occurred on

September 23rd, 24th and 29th, with ash deposited more than 20 km from the crater.

During October 1985, a steam plume 0.8-2 km high was seen continuously. Seismic activity also

continued; however it was less than the seismic activity recorded in September. [10, 11]

November 13th - sequence of events,

15.06 - two explosions occurred in the crater with associated ash emissions.

16.00 - wet ash began to fall in Herveo, 26 km to the Northeast of the crater.

17.00 - ash began to fall in Armero.

21.08 - the first explosions of the main eruption.

21.30 - the second and bigger explosion, a volcanic explosivity index 3 (see figure 4.2 below), was

accompanied by the formation of pyroclastic flows and lahars on the summit and upper flanks.[4]

22.40 - lahars arrived in Chinchiná on the Rio Claro,

23.25 - lahars arrived in Armero on the Rio Lagunillas, overrunning the entire city [10]

Figure 4.2 The Volcanic Explosivity Index [12]

of 21


4.3 The November 13th 1985 lahars

The four eruptions of Nevado del Ruiz on November 13th 1985, changed the ice cap around the

summit crater, Crater Arenas, it was fractured and destabilised by the eruption and accompanying

earthquakes. It is believed that four distinct processes were responsible for transporting snow and

ice downslope. These processes were explosions, ice avalanches, surficial erosion of snow, and

slush avalanches. The pyroclastic materials from the eruption were mechanically mixed with the

snow and ice, both at the surface, and in deep fissures. These fissures were the result of the

September 11th eruption. Heat from the pyroclastic materials was responsible for melting the snow

and ice.

Data from photographs and fieldwork before and after the 1985 eruptions indicate that 9% of the

ice cap melted, producing 43 x 106 m3 of water. These estimates differ from the initial water

content of the lahar, which was 12 x 106 m3. Some of the melt water may have been absorbed into

the sides of the volcano and therefore be available for future lahars [3].

Table 1 summarises the volumes of the melt water and water in the consequent lahars, calculated

from evidence of vegetation damage and clast orientation up the valley walls [3]. The early lahars

created smooth channels, by eroding the surface of the valley walls. This in turn allowed the later

lahars to travel faster and overtake the earlier ones, resulting in pulses of lahars arriving at Armero

[3].

* Nereidas and Molinas combinedDrainage channel Glaciated Drainage

Area in km2Estimated Water

volume in initial lahars (m3 x 106)

Water from Ice and snow missing from ice

cap (m3 x 106)Nereidas 3.4 3-7* 2.8Molinas 2.1 3-7* 4.1Guali 1.8 3-7 6.7Azufrado 3.5 5-8 17.9Lagunillas 3.9 0.2 12.1

Total 14.7 11-22 43.6Table 1 Summary of volumes of melt waters for the five main channels producing lahars.

The volume of the lahars increased dramatically during their journeys. Their total volume

increased from between 19 and 27 x 106 m3 at source to 89 x 106 m3 just before deposition, a

‘bulking’ of up to 300% by volume [3, 4]. 6-8 lahar pulses hit Armero, the first pulse arrived at

23.25, with the last major pulse striking at about 01.00, with a velocity of 4-5 m s-1. Lahar deposits

at Armero are illustrated in Figure 4.3

of 21


Figure 4.3 Aerial view of Armero November 14 th 1985 [13].

4.4 The effects of the November 13th 1985 lahars

Lahar hazards in general include destruction of buildings, destruction of local infrastructure and

communities by burying roads and/or washing away bridges, as well as loss of life. Burial of

agricultural land and destruction of crops and cattle, can have a long-term effect on local

communities.

The effects of the events of November 13th are listed below [11].

Over 23,000 fatalities

Over 5,000 injured

Over 7,500 rendered homeless

60% of the regions livestock lost

30% of sorghum and rice crops destroyed

3,400 hectares of agricultural land buried

Over 5,000 homes destroyed

50 schools, 2 hospitals, over 50 industrial plants and 343 commercial properties destroyed.

of 21


5. What was in place before the eruption ?

This eruption was not an unexpected event, nor were the lahars that accompanied the eruption.

Historical evidence showed that fatal lahars had occurred in the area around Nevado del Ruiz, in

both 1595 and 1845, so what was in place before the November 13th eruption.

5.1 International help

In March 1985 a geologist from the United Nations Office of the Disaster Relief Organisation

(UNDRO), and two Swiss geologists investigated the volcanic activity around Nevado del Ruiz,

they recommended that the volcano be monitored.

In April Costa Rica offered three seismographs, and technical support in the use of this equipment.

The USGS said they would send both personnel and equipment to the area if formally invited by

the Colombian government. This request did not materialise until after the September 11 th eruption.

A USGS geologist arrived late September [10,11].

The September 11th eruption, raised the profile of Nevado del Ruiz, international scientific

assistance arrive from New Zealand, Ecuador, Italy, and more from Switzerland. The net result of

all these foreign scientists working with different Colombian agencies was confusion. Almost all

attention was focused on the risks from pyroclastic flows and ash, very little on possible lahars,

even though this eruption had produced a lahar.

5.2 Monitoring and results of monitoring

5.2.1 Seismology

By August 1985 a seismological net of five stations was in place around Nevado del Ruiz, all

manual, none were telemetered. At this time there were two seismological groups working on or

around the volcano, they were the National Institute of Geology and Mines, INGEOMINAS and

CHEC, the state-run electrification company, they worked independently and did not share their

information [10]. On September 4th INGEOMINAS relocated their three seismographs to 10 km from

the crater. Lack of funding meant there was little training in the use of seismological equipment,

and interpretation of seismic data locally, so all seismographs were sent to Bogotá.

In early November INGEOMINAS noted bands of tremors just a few days before the eruption. The

fact that so few seismographs were in place and the lateness of their deployment, meant that there

was no baseline data for comparison [10,11].

of 21


5.2.2 Gas Analysis.

Monitoring of gas fumaroles had taken place intermittently and by different geologists throughout

1985. Regular gas sampling did not occur until after the September 11th eruption. The samples were

sent to Bogotá for analysis. This could take several weeks.

In October it was noted that there had been a constant increase in the H 2O/HCL and CO2/HCl

values up to October the 19th, but then these values started to decrease. These results were not

available before November 13th[10].

5.3 The Hazard Map

Possibly the most vital document produced by the geologists monitoring Nevado del Ruiz was the

volcanic hazard map. In late September 1985, six geologists from INGEOMINAS conducted a survey

of the volcano with a view to producing a map of volcanic hazards. They produced a map by

October 7th, which can be seen below (figure 5.1) [9].

Figure 5.1 Preliminary map of volcanic hazards of Nevado Del Ruiz [9]

of 21


This map was published on the front page of a national newspaper on October 9 th. It was noted that

there were mistakes in some of the symbols, but it showed the most dangerous areas [10]. It was

evident that the map needed revising. This was done and a new map was finished in early

November, and was due for presentation on November 11th 1985. This map is shown below, figure

5.2.

Figure 5.2 Map of potential volcanic hazards of Nevado Del Ruiz volcano[9]

The main modifications included the use of a smaller scale, better definition of zones threatened by

lahars, and reduction of areas threatened by pyroclastic flows. The revised map legend now clearly

shows the threat of lahars for the town of Armero.

On November 6th the Palace of Justice, in Bogotá was the scene of a bloody encounter between

government troops and guerrillas. 100 people, including 11 supreme court judges were killed.

Because of this event, the public presentation of the revised and clearer hazard map was postponed

until November 15th [11], 2 days too late.

of 21


5.4 Local government versus national government

There were clear and major differences between national and local government, following the

September 11th eruption of Nevado Del Ruiz.

The local governments in the area acted swiftly, to produce an action plan, and study the possibility

of emergency evacuation, however they quickly came to the conclusion that they were under

funded and ill equipped for this task. Each local authority then set about their own action plans with

no coherent overview from central government. [9,10,11]

The national government was slower to react to the September eruption. A week after the eruption

they convened a meeting to discuss the volcano. The main actions to come from that meeting was

the minister of mines instructed INGEOMINAS to produce the volcanic hazard map, and five working

groups were formed, to cover budget, public health, agriculture and livestock, water, and a

scientific working group. [10].

5.4.1 Information to the public

With so many different agencies sending out information, it is no surprise that the public were

getting different messages. A problem highlighted by the local press. On September 18 th La Patria,

a daily newspaper of the area, published an article about the problem of spreading false

information, and the devaluation of real estate prices, due to what it termed “volcanic terrorism”.

On October 5th the Archbishop of Manizales made a statement criticising some television, radio,

and press for their role in spreading volcanic terrorism. On the same day a scientist from Manizales

told the public to remain calm in the face of alarmist news items being exaggerated by radio

announcers[10].

The alarmist news items referred to were reports in some local papers that “lahars and floods are

inevitable” and “a 100% probability of mudflows”. This was compounded by an interview with the

mayor of Armero in which he stated that the local emergency committee “did not have the

necessary information or financial resources to do anything in the event of a catastrophe. . . For this

reason, the people have lost confidence in the veracity of the information and have commended

their fate to God”[11].

On the day of the eruption, the public were being told to stay calm and stay in their homes, (it was

still believed that ash fall was the greatest danger), see flow chart figure 5.3. The local radio in

Armero was playing “cheerful music” until it suddenly went off air as the power went out, and it

was engulfed in mud.[11]

of 21


Figure 5.3 Simplified management system and communication links November 13 th 1985 [11].

It is easy to see from the above flow chart how problematic communication must have been, even if

all lines of communication were working, which seems unlikely, as lahars tend to wipe out

telephone poles and power lines. The open or half open dot symbols, indicate no communication, or

uncertain communication, and the black dots indicate communication OK. It would appear that the

21.45 message to evacuate from the regional emergency committee, never reached the residents of

Armero.

of 21


6. What could have been done today ?

6.1 Public education

What has been learnt in the twenty years since Nevado Del Ruiz? One clear lesson was the need for

a coherent emergency plan, well communicated and understood by those people directly at risk

from the volcano. In Japan children are taught at school what to do in the case of earthquake or

volcanic eruption, so from a young age they have a clear understanding of the emergency

procedures.

In the case of Nevado Del Ruiz many lives could have been saved if there had been a clear

emergency plan to evacuate to higher ground, but that required an understanding of the dangers of

lahars by the general public, which was evidently lacking.

6.2 Seismic surveillance and acoustic flow monitoring

Any emergency plan requires the alarm to be raised when danger arises. Today seismic surveillance

can be done both at ground level using telemetered seismographs, producing real time data, and

from space via satellites.

6.2.1 Earth Observation Satellites

There are currently more than 75 Earth Observation Satellites orbiting the Earth, with various

systems for observing the earth, from standard photography to radar altitude measurement.

Data from satellites can be used to produce geographical information systems (GIS) and digital

elevation models, (DEMs). DEMs are used to assess risks from volcanoes, and produce hazard

maps, and evacuation plans. By monitoring the slight changes in elevation of a volcano DEMs can

be used to assess the movement of magma within a volcano. DEMs can also be used to predict the

most likely paths of any lahars produced, and this can be used to plan emergency evacuation route

from towns and villages [14,15]. GIS can be used as a reference, in the cases of total destruction of

towns or villages, GIS can be used to identify exactly where building stood, and so aid rescuers in

the search for casualties [14].

6.2.2 Ground based seismic surveillance

Since Nevado Del Ruiz there have been great advances in seismic surveillance technology. Two

systems in particular are used, seismic spectral amplitude measurement (SSAM) and acoustic flow

monitoring (AFM).

of 21


SSAM is a computer system that uses real-time seismic amplitude measurements, from a

telemetered seismograph. It digitises the incoming signal, analyses it and picks out the frequencies

it is programmed for. These can be set for the low frequency rumbles typical of lahars, and this can

used as an early warning system if the seismographs are stationed in the upper sections of lahar

channels [16].

Acoustic flow monitoring (AFM), is a system developed by the USGS in the 1990’s. AFM uses a

network of geophone sensors placed in the lahar channel, and microprocessors on the riverbank.

The geophone picks up low frequency vibrations, which it sends to the microprocessor, this then

compares the signal to those in it’s memory, if the signal matches a lahar, the microprocessor will

send an alarm signal to a predetermined alarm system. The advantage of AFM over SSAM, is the

AFM can give a continuous record of the wave flow, and it can also be used to analyse the

sediment to water ratio of the lahar [16].

6.2.3 LAHARZ

The data gathered both by satellites and from seismic surveillance, can be used in a GIS program

called LAHARZ. This program is used to predict if lahars, are likely to occur after an eruption and

if they do occur just how large they will be and how far they will travel. LAHARZ can help plan

land use around a volcano and help save lives [17].

6.3 Sabo check dams

One physical lahar defence are sabo check dams. These dams, a major feature of lahar management

in the steep sided mountains of Japan, where they have been used since the 17th century. The word

sabo translates to sand protection. They come in many different types, and sizes, usually made from

reinforced concrete. They are sited in the channel of known lahars, and have an opening either in

the top or bottom, to allow water through, but not large boulders, or other larger debris. They have

been tried in Europe, North and South America, were steep side river channels are subject to lahars

[18,19]. Sabo check dams work by temporally storing sediment, and then releasing sediment

through natural river flow. See figure 6.1 below. Recent advances in sabo check dams have seen

them constructed of tubular steel in the form of a steel grid [18], see figure 6.2 below. One of the

disadvantages of sabo dams is that they are required to be sited in the course of known lahars, and

they are usually one part of a lahar defence system. Also currently they are permanent and very

expensive.

of 21


(i) A newly constructed sabo is filled with sediment from upstream, making the gradient of the river bed gentler to prevent hill slide collapse of the river banks

(ii) When sediment is discharged due to a downpour etc. the sabo dam temporarily stores much more sediment.

(iii) The surplus sediment which is temporarily stored is then gradually released by the subsequent natural flow of the river water.

Figure 6.1 diagram showing how sabo check dams work. [20]

Figure 6.2 A tubular grid sabo check dam. [18]

of 21


7. Conclusion

The eruption of Nevado Del Ruiz volcano, was the second worst volcanic disaster, in terms of

numbers killed in the 20th century, only exceeded in fatalities by the eruption of Mt Pelee in

Martinique in 1902 [21]. The people who died on the night of November 13th 1985, were killed by

lahars, a secondary event of the volcanic eruption. An event that today, 20 years later, could have

been accurately predicted.

Why was this event so catastrophic, was it the shape or location of the volcano? Nevado Del Ruiz is

a stratovolcano standing over 5,400m above sea level, with steep sided river gullies, this

contributed to the distance that the lahars travelled, being contained within these deep gullies.

However it is no steeper than many other stratovolcanoes around the world. Armero is over 100 km

from the volcano, far enough away not to have been affected by pyroclastic flows, but close enough

to have experienced ash fall. These are contributing factors, but not the answer.

It was know that an eruption of Nevado Del Ruiz could produce deadly lahars, it had done so

previously in both 1595 and 1845. Both those events killed 70% of the population living in the area

where Armero is now built. Add to this the fact that just two months earlier an eruption had caused

a small lahar. The people living around the volcano must have been aware of the dangers it posed.

The local press had published many articles about the dangers since the September eruption, but it

does seem that they may have exaggerated the dangers of pyroclastic flows and ashfall deposits,

and under-played the danger posed by lahars.

Was the size of the eruption and the quantity of hot ejecta the primary reason so many lives were

lost? As stated in chapter 4.2, this eruption was a small one, a 3 on the VEI, producing between

1x107 and 1x108 m3 of tephra (see figure 4.2), which when mixed with 43 x 106 m3 of melt water,

produced lahars with a total volume of 89 x 106 m3. This volume of mud, must have been the major

reason why so much of Armero was destroyed, and why so much land and livestock was lost.

Another contributing factor to the high death toll was the fact that the lahars hit Armero at night.

The first one struck at 23.45 hrs, and the last at 01.00 hrs. It was a Wednesday night and most

people would have been asleep at that time. Some of those who survived were out in the local bars

when the first lahar hit, and they managed to get to higher ground [11]. The death toll may have

of 21


been lower if the lahars struck during the day, when many more people may have been out at work

or just outside.

The main reasons so many lives were lost has to be the lack of a clear emergency plan and the lack

of an early warning system; both of these factors stem from a lack of financial resources. If the

residents of Armero had an emergency plan, which was communicated to them, and they

understood it, lives would have been saved. A simple plan such as “on hearing the alarm, move to

higher ground” would have saved thousands of lives, if raised early enough.

It is a fact that the poorer countries of the world, cannot spend large sums of money on, what is

basically insurance. If Nevado Del Ruiz was in the USA, it is very unlikely that a November 13th

type eruption would have killed more than a few hundred people. LAHARZ which was developed

by the USGS, would have predicted the high risk of lahars. It is possible that sabo check dams

would be constructed high up on the volcano run-off channels, to physically reduce the volume of

volcanic debris being swept downslope. An early warning system such as AFM, would have been

placed on the volcano, and telemetered to a USGS observation center close by, and relayed to the

local Federal Emergency Management Agency office, who would execute a pre-determined

emergency plan.

Tragically in November 1985 Armero had none of those things, which is why so many people died.

of 21


References[1] Earth Sciences for Society (2007) Hazards – minimising risk, maximising awareness. Available from www.esfs.org [Accessed 30 August 2007]

[2] Smith and Fritz, (1989) as described in Watershed Disturbance and Lahars on the East Side of Mount Pinatubo During the mid-June 1991 Eruptions. Major J J, Janda R J, and Daag A S. (1999) Available from http://pubs.usgs.gov/pinatubo/major/ [Accessed 11 April 2007]

[3] Thouret J-C.(1989) Effects of the November 13, 1985 eruption on the snowpack and ice cap of Nevado del Ruiz volcano, Colombia. Journal of Volcanology and Geothermal Research, 41 (1990) 177-201

[4] Pierson T C, Janda R J, Thouret J-C and Borrero C A (1989) Perturbation and melting of snow and ice by the 13 November 1985 eruption of Nevado del Ruiz, Colombia, and consequent mobilization, flow and deposition of lahars. Journal of Volcanology and Geothermal Research, 44 (1990) 17- 66

[5] Major J J, Janda R J, and Daag A S. (1999) Watershed Disturbance and Lahars on the East Side of Mount Pinatubo During the mid-June 1991 Eruptions. Available from http://pubs.usgs.gov/pinatubo/major/ [Accessed 11 April 2007]

[6] Scott K M, Vallance J W , Kerle N, Macías J-M, Strauch W and Devoli G. (2004) Catastrophic precipitation-triggered lahar at Casita volcano, Nicaragua: occurrence, bulking and transformation. Earth Surface Processes and Landforms 30, (2005) 59-79

[7] Francis P, (1993), Volcanoes, A Planetary Perspective. Oxford University Press, 443 pp

[8] Tanguy J-C, Ribière Ch, Scarth A, and Tjetjep W S. (1998) Victims from volcanic eruptions: a revised database. Bull Volcanol (1998) 60: 137-144

[9] Parra E, Cepeda H. (1989) Volcanic hazard maps of the Nevado del Ruiz volcano, Colombia. Journal of Volcanology and Geothermal Research, 42 (1990) 117-127.

[10] Hall M L. (1989) Chronology of the principal scientific and governmental actions leading up to the November 13, 1985 eruption of Nevado del Ruiz, Colombia. Journal of Volcanology and Geothermal Research, 42 (1990) 101-115.

[11] Voight B (1989) The 1985 Nevado del Ruiz volcano catastrophe: anatomy and retrospection. Journal of Volcanology and Geothermal Research, 44 (1990) 349 – 386.

[12] Image courtesy of http://www.volcano.si.edu/world/vei.jpg Accessed 15/5/2007.

[13] Image courtesy of USGS. Downloaded from http://vulcan.wr.usgs.gov/Volcanoes/Colombia/Ruiz/images.html Accessed 15/5/2007

[14] Pareschi M T, Cavarra L, Favalli M, Giannini F, Meriggi A. (1999) GIS and Volcanic Risk Management. Natural Hazards 21: 361–379, (2000)

[15] Kerle N, Oppenheimer C. (2002) Satellite Remote Sensing as a Tool in Lahar Disaster Management. Disasters, (2002), 26(2): 140 – 160

of 21

http://vulcan.wr.usgs.gov/Volcanoes/Colombia/Ruiz/images.html

http://www.volcano.si.edu/world/vei.jpg

http://pubs.usgs.gov/pinatubo/major/

http://pubs.usgs.gov/pinatubo/major/

http://www.esfs.org/


[16] Lavigne F, Thouret J-C, Voight B, Young K, LaHusen R, Marso J, Suwa H,Sumaryono A, Sayudi D S, Dejean M. (2000) Instrumental lahar monitoring at Merapi Volcano,Central Java, Indonesia. Journal of Volcanology and Geothermal Research, 100 (2000) 457 – 478

[17] Oramas Dorta D, Toyos G, Oppenheimer C, Pareschi M.T, Sulpizio R, Zanchetta G. (2006) Empirical modelling of the May 1998 small debris flows in Sarno (Italy) using LAHARZ. Natural Hazards (2007) 40:38 1-396

[18] Chanson H.(2004) Sabo check dams- mountain protection systems in Japan. Intl. J. River Basin Management Vol.2, No.4(2004), pp. 301-307

[19] Takahashi T, Nakagawa H, Satofuka Y, Kawaike K. (2001) Flood and Sediment Disasters Triggered by 1999 Rainfall in Venezuela; A River Restoration Plan for an Alluvial Fan. Journal of Natural Disaster Science, Volume 23, Number 2, (2001), pp65-82

[20] Image courtesy of USGS Downloaded from http://pub.usgs.gov/fs/fc-176-97/fs-176-97.html Accessed 21/8/2007

[21] Witham C S. (2005) Volcanic disasters and incidents: A new database. Journal of Volcanology and Geothermal Research 148 (2005) 191– 233

of 21

http://vulcan.wr.usgs.gov/Volcanoes/Colombia/Ruiz/images.html

eca

Documents

lahars page

nature of lahars

subsequent lahars

trigger lahars

future lahars

devastating lahars

life threatening lahars

small eruption of nevado