Tenerife: formation, stratigraphy and water resources

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Tenerife: formation, stratigraphy and water resources

TENERIFE:

Formation, stratigraphy and water resources

Written by Malcolm Sutherland

Student matriculation no. 9805423

All photographs and illustrations produced by the author, except where referenced


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LAYOUT OF THE REPORT

1: FORMATION OF TENERIFE

1.1: Geological History of Tenerife

1.2: Formation of the Las Canadas caldera

2: GEOLOGY OBSERVED IN THE FIELD

2.1: Volcanic Deposits

2.2: Sedimentary deposits and soil development

3: WATER RESOURCES

3.1: Evolution of water resources on Tenerife

3.2:Applications and limitations

REFERENCES

APPENDICES

Plate A: Sections 1 to 3

Plate B: Section 4

Plate C: Sections 5 to 8

Plate D: field mapping (El Medano)


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1: FORMATION OF TENERIFE

1.1: Geological History of Tenerife

The origins of magmatic activity at Tenerife date as far back over 20 Ma in the Oligocene.

Akin to Hawaii, Iceland and the Azores, the Canarian archipelago represents an oceanic

hotspot, a magmatic focal point where a mantle plume injects magma through the crust to

produce a prolific series of volcanoes. The movement of the oceanic plate eastwards results

in youngingof volcanic islands, from Lanzerote (20Ma) to Hierro (0.5 Ma).

Tenerife itself originally consisted of 3 focal points of activity situated around the comers of

its triangular geometric outline (Figure 1). The oldest outcrops seen on the island dateback

lo the late Oligocene (7-8 Ma), although this was 8 million years after submarine volcanism

in the area was initiated. Alkali basalts dominate in the Old Basaltic Series - these are found

at the Roque del Corde, Anaga and Teno peninsulas, which are linked to the central cone bycrustal fractures, along which several cones are approximately aligned. Volcanism became

more centred, until the 3 islands were linked by a central cone.

A quiescent period elapsed around 4.5 Ma, during which extensive weathering and erosion

occurred. Activity re-commenced around 3.3 Ma, producing a new central cone (Las

Canadas) interconnecting all three islands, and composed of basaltic, pyroclastic and

phonolitic deposits in more violent eruptions (Lower Group). This has geographically been

the main focus of eruptions since then, involving cycles of cone accumulation, followed by

structural instability and caldera collapse. Hundreds of minor eruptions have occurred

throughout Tenerife also, manufacturing smaller volcanoes along the coast and around theslopes of the Las Canadas caldera.

Figure 1: the three principal stratigraphic groups on Tenerife


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1.2: Formation of the Las Canadas Caldera

Mt. Teide and Pico Viejo do not represent one single volcanic peak which is geographically

and geologically central to Tenerife- Were this the case, they would rise to a greater

altitude, possibly 5000m- Until around 780,000 years back, a great volcano of this structure

did exist. The area covered by the recent Teide-Viejo vents is dwarfed by what was the areacovered by one volcano at around 2000m, clearly represented by the Las Canadas

amphitheatre (Figure). 3 caldera collapse events occurred - 1.07 Ma, 650,000 and 170,000

years ago.

The Caldera itself is not visible from further downhill; however, the inner wall of the

amphitheatre structure rises abruptly above the caldera floor by up to several hundred

metres. Originally this was deeper, as basaltic and acidic deposits erupted by Teide, Pico

Viejo and Chahoma have obscured the collapsed framework underneath.

The enormity of what was the Las Canadas Edifice - and the vertical scale of theamphitheatre (Figure 2) - attracts tens of thousands of tourists each year. In recent

decades, the area was designated a Spanish national park, whereby all faunal and floral

species, and the geology itself, is given the highest protection. Visitors today are under strict

regulations not to disturb anything within the area; rock-sampling is an infringement for

which the park rangers can impose penalties or take further action. Road inspections by the

rangers are a daily routine.

Figure 2:view of the southern section of the Las Canadas amphitheatre

The caldera flanks has also led to debate among geologists as to how such a great descent in

height could have occurred along a single main fault. Although in the geological record, thecaldera collapse events are aligned with unconformities (hence a significant time-gap is

missing from the stratigraphy), an average tectonic fault allows for movement of adjacent

masses between 5 and 10 m. If a series of vertical faults caused the slippage, the caldera

wall would have been eroded following each earthquake to leave possibly no structure. The

evidence (for 600m of almost instantaneous faulting) points to an anomalous tectonic

event, in which the older basalt volcano structure was no longer supported by upcoming

magma, and collapsed under its weight. Possibly 1000m of recent flow basalts cover this.

Landslides extending for tens of square kilometres (Figure 3) resulted from these events,

with ignimbritic release following destabilization. Landslides have also occurred alone -


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Malpas de Guimar, and Valie de la Orotava form broad sloping valley structures where there

is an absence of narrow ridges leading up to the central flank.

Figure 3: formation of the caldera


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2: GEOLOGY OBSERVED IN THE FIELD

2.1: Volcanic Deposits

LAVA TUBES (Figure 4)

Defining the precise age of activity, and

locating where the flow started and

finished, is a difficult task, requiring

observation of petrographic and chemical

properties, as opposed to measuring

indicators such as radionuclides. The lava

tube shown above is one of the Las

Canadas infrastructure of breccia-lava

flows: encompassed by ignimbritic rock,this was a channel for emerging lava, the

remains of which arc eroded boulders or

stalagtite-like needles hanging from the

roof of the exposed tunnel.

Figure 4: one of the lava tubes a few miles south of

Mt Teide

VOLCANIC ACTIVITY WITHIN RECORDED HISTORY (photo ofChineiyu)

The last eruption to occur on Tenerife was at a secondary vent on the south flank of

Chineryo, 400m below the summit. The 1909 eruption and others in the last few millennia

have been relatively minor compared with the more widespread and occasionally explosive

cycles recorded at El Medano and Bandas del Sur. These nevertheless have been frequent

(around 200 years), indicating that further activity may occur, perhaps within the next 2

centuries. The magma chamber beneath Chineryo is between 1 to 2 km underground

(Figure 5).

Figure 5:the magma chamber beneath the Chinyero peak


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The fresh basaltic ash is pitch black, vitreous, and forms discrete homogenous layers of sub-

rounded 1-6mm pellets. These properties of the 1909 eruption deposits have not been

disturbed by weathering and vegetation, although coniferous trees have been planted for

conservation and to promote soil development. In contrast, the ash extruded in 1799

(Figure 6) appears brown due to mobilization of Fe3+

by colonising vegetation including

while broom bushes. Previous ash layers (photo) buried beneath additional deposits may

remain melanocratic, although white precipitates formed by hydrothermal fluids can bepresent.

Figure 6:Chinyero (with the black 1909 vent further downhill)

Other historic deposits found within the caldera include basaltic flow deposits, characterised

by "Po-hoe-hoe" and the physically treacherous "Aa-aa" features (Figure 7, left), bothreflecting different properties of viscosity and water content. The ropy po-hoe-hoe lava

appears more planar, due to its mobility before solidifying (Figure 7, right). The lineation

fabric seen in the photo was created by the stretching of emerging gas cavities, and

indicates the direction of flow. The "Aa-aa" rapidly crystalised and fractured to its abrasive

texture as heat was lost rapidly.

Figure 7: Aa-aa and Po-hoe-hoe lava deposits downstream from Chinyero


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The front of lava deposits consist of a steep embankment lined with breccia, caused by the

movement of still-molten rock over solid layers underneath, and the deposition of material

there-from. The Montana BIanca eruption occurred 2000 years ago, although it is presumed

that Tenerife was uninhabited by the Guanches at that time, and so was not witnessed.

ERODED DYKE PILLARS

Viewed in the picture on the title page, groups of these formed an infrastructure of lava

channels for volcanic cones. The cone was eroded away, and faster erosion of the lava

deposits around the pillars leaves these structures protruding above the surface.

OBSIDIAN FLOW DEPOSITS

Obsidian, as a rapidly chilled volcanic glass with no crystalline features, can only be

produced in a sub-aqueous environment. This is found on the lower slopes of Mt. Teide,

suggesting that the caldera comprised a euphmeral lake, possibly during one of the last

glaciation periods when the climate was less arid. The assortment of gray, violet, yellow andturquoise streaks seen on the rock represent hydrothermal alteration both during and after

deposition.

MONTANA BLANCA (Figure 8)

This features a small sandy desert composed of pumice ash-fall deposits, left by a sub-

Plinian eruption at Minas de San Jose, a volcano along the amphitheatre. The pumice sand is

poorly sorted, consisting of pale yellow, angular, very fine to pebble-sized grains (up to

5cm). It is also intimately mixed in with some basaltic ash granules of similar size. In some

areas this has weathered to form pale green or red sand. Underneath the looselyunconsolidated dune surface are moist, compacted layers of this weathered pumice.

Figure 8:Montana Blanca

The pumice ash was violently projected by the volcano and scattered between 1 and 2km

west, due to the viscosity and high gas content of the magma. Agglutinates (basaltic

boulders seen around the summit) were later ejected as the magma was depleted of gas.The lava flow occurred last when the gas was almost removed.


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VENT DEPOSITS (Figure 9)

Volcano vents are scattered across Tenerife, several of which protrude at the coastline. One

of these is found west of El Medano, which may have been produced after beach deposits

recorded in the field mapping exercise (see Appendices, Plate D). Nearly all of the cones

date from the late Quaternary and the Holocene since the last caldera collapse 170,000

years ago. These are primarily composed of scoria, i.e. black, vesiculated, basaltic ash, whichis often layered and poorly consolidated. The fragmented basaltic rocks were produced by

pulsated explosions of magma in contact with the air due to its water composition. The

explosions are caused by water passing into the magma when gas escapes from it, causing

rapid expansion and emission of fine particles due to the cooling effect of the water.

The scoria can include the accumulation of highly developed augite crystals, which formed

prior to the eruption by hundreds of thousands of years. It appears often as fine-grained

clumps, or basalt granules, and hydrothermal alteration leads to the formation of while

carbonate streaks.

Figure 9: thin weathered layers of basaltic ash steeply dipping

WEATHERING

Ash-fall deposits weather to a fine-grained clay-rich soil over a few hundred years due to Fe

leaching by water, induced mainly by vegetation in Tenerife's arid climate as water is

retained by the plant and percolates down through the rhizosphere. On the coast, contactwith the sea leads to rapid degradation of the cone structure under heavy oxidation; in

stratigraphy, vent deposits are not found underneath marine strata.

VOLCANIC BOMBS WITHIN BEACH DEPOSITS

This localised feature found east of El Medano was produced by a synchronous event, in

that the basalt fragments were introduced at the time when the beach sand was also being

deposited. They are arranged in lobes which have sunk into the sand, suggesting that they

were still molten on arrival. The dendritic shape of the boulders indicates that this was anextrusive event. However, the burial of some bombs beneath the sand would have


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prevented this shape from developing - several of these have been exposed out-with the

sand by erosion, a feature which has not yet been explained.

VOLCANIC CYCLES

The stratigraphy across the southeast area of the island is dominated by recent alkaii basaltsextruded from over a hundred individual cones spread across the Arena region. Between

these deposits are pyroclastic and phonolitic strata comprising ignimbrite, pumice, base

surge and ash layers, altogether which were derived from separate events throughout the

last million years which affected much of the area as a whole. Each event is separated in the

stratigraphic record either by erosion or caldera collapse, or by sedimentary deposits

accumulating during quieter periods.

The strata across the region generally link together, although thicknesses in each deposit

vary from non-existence to as much as several metres in height. Local topography is an

important determining factor of the accumulation and amount found in any given area.Their distinctively bright colour reflects their acid igneous composition, generally with a SiO2

percentage of around 60.

Ignimbrites (Figure 10)

A pale-yellow, gray or pink pyroclastic

deposit, consisting of vesicles, and often a

small to enriched concentration oflithic

fragments. Clasts can be either, or a

mixture of, felsic/pumice fragments, andbasaltic xenoliths.

Other features can include faint banding

(individual eruptions), and trace or

embedded fossils caught within the

eruption. Accretionary lapilli (mm-few cm

diameter) appear as hollowed-out discs

within which an ash particle protrudes;

ash particles ejected by the eruption

attained layers of fine ash before reachingground level.

Figure 10: outcrop showing volcanic layering

In contrast to most deposits of any origin, ignimbrites represent one instant event

composed of one or more pyroclastic explosions which were powerful enough to plane the

underlying landscape indiscriminately, including small hills. These density flow eruptions

were caused by structural collapse following a period of volcanic activity, and could reach up

to 800 C and achieve a velocity of 300MPH, scorching and destroying all vegetation and

faunal life in its path.


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Silicic Ash Deposits

Often white, very fine grained and compacted to form thin discrete layers, usually beneath

an ignimbrite or pumice layer. Ash can either exist as ash-fall, or ash-flow deposits, whereby

the latter is spread in conjunction with the topography. Rippled and wavy banding and

lamination may suggest a lacustrine environment of deposition. Base surge deposits of ashproduced by initial explosion at the volcano before magma is erupted.

Pumice

This is often a pink, pale brown or yellow unconsolidated deposit consisting of sub-angular

to cubic pumice clasts, which contain a delicate fibrous framework, with enough air inside

for it to float on water. Layers of pumice are rapidly produced by violent silicic eruptions.

Debri Flow

A very poorly sorted lahar deposit, composed of angular clasts of varied lithology within a

coarse brown mud matrix. Floods occuring in conjunction with lava flow conbined to form a

potent hot stream, which inflicted heavy erosion, and carried the debri before scattering

them across a wide area.

CYCLES OBSERVED IN THE FIELD

The period of activity recorded lies between around 0.76 Ma (the Saltadiero ignimbrite) and

170,000 years ago. (The sections are on Plates A and B in the appendices.) The Saltadiero

eruption began with a cataclastic explosion, producing an ash-fall deposit (Section 7), andaccompanied by pumice eruptions (Section 6); this was followed by violent pyroclastic

eruption which brought down debri from the volcano side. Around 0.596 Ma, a basaltic

eruption occurred, followed by another pyroclastic eruption (the Abades ignimbrite)

(Section 7).

Pumice eruptions occurred before another cataclastic explosion, which was also a prelude

to a pyroclastic flow which formed the Poris and Upper Grey units around 320,000 years ago

in some areas (Section 3), with more pumice deposits elsewhere (Section 4). Eruptions then

ceased for long enough for the deposits to weather and soil development took its course.

Thereafter further pumice eruptions occurred along with further explosions producing ashlayers. Another pyroclastic eruption which blasted the volcano (releasing debris) produced

the La Calata ignimbrite around 170,000 years ago (Section 1).

2.2: Sedimentary Deposits and Soil Development

The sediments detailed in this sub-section dale from within the last million years.

Throughout that time the coastal climate has mainly been similar to the arid one today-

These intermingle with the volcanic cycle deposits, although variations persist over short

distances due to ancient channels, erosion and changing sea level.


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FLUVIAL DEPOSITS

Tenerife along its coast is characterised by fluvial channels, which are dry throughout the

year with the exception of flash floods during occasional storms, leaving behind

conglomerates and coarse-grained sands as debris was carried down by the torrent. Fossils

found here include land snails and wasps nests, indicating the arid climate which persists

within tin-se fluvial valleys almost without interruption. In the past, such valleys have alsochannelled igneous deposition, including ignimbritics found outside El Medano.

Figure 11: fluvial deposits outcrop

Coarse sands often feature cross-bedding, and are composed of a mixture of basaltic and

silicic granules. The conglomerates contain clasts possessing the same mineralogy (plus

some pumice). These appear angular, and range from mm-scale pebbles to boulders, some

which measure over 40cm in diameter. Beds of these layers are unevenly distributed,

reflecting the erosive and changing properties of the cascading flood.

Clay deposits along the valley floors are found where water puddles left by the flood

evaporate, depositing fine suspended material, often with microfossils including spores.


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AEOLIAN AND BEACH DEPOSITS

Strong southerly winds carry dust which abrades exposed rock surfaces, leaving

unconsolidated sand deposits and small dunes inland from the beach. Section 6

(appendices, Plate C) contains reworked beds due to wind erosion. Rock exposures and their

strata are gradually converted into rounded lobular structures, and clasts from

conglomerates and volcanic debris flow arc etched from within the matrix.

The beach sand is often a coarse sand of a pale brown colour, dominated by silicic grains,

but also containing basaltic grains; a rich concentration of shell fragments derived from

bivalves and echinoderms. Pumice-rich varieties are also present east of El Medano

(appendices, Plate C, Section 8). Near the Roja vent, a dark red, more basaltic variety is

found.

PALAEOSOLS (Figure 12)

These developed further inland as vegetation and fauna colonised areas covered by volcanicdeposits, or beach sand (particularly during marine regression). These appear as

consolidated brown layers of around 0.5 - 1m in height, due to moisture and organic matter

content. Loose clasts at the base fine upward to particle size; calcified fossils include

burrows, rootlets and land snails. Calcrete structures and carbonate deposition, created by

water evaporation from plagioclase are diagnostic properties of the arid environment.

Figure 12: calciferous precipitation seen at Bandas del Sur


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3: WATER RESOURCES AND LIMITATIONS

3.1: Evolution of Groundwater in Tenerife

During the late Miocene (circa 5Ma), the basaltic foundation of the island was produced as

Tenerife converged from 3 distinct volcanoes to form a single island based on a central cone(Figure 13, upper diagram). The accumulating material was initially porous, but during a

quiescent period (5 Ma to 3 Ma) in volcanic activity, this was weathered and eroded to

produced an impermeable base (Figure 13, lower diagram). The late Pleistocene and

Quaternary volcanic deposits, comprising both basic and salic lavas covers over the

impermeable base around the central cone, and is still porous. Water (derived solely from

the atmosphere from condensation, rain, and at high altitudes, snow in winter) percolates

through the rock, particularly following dykes and veins until it reaches the water table. The

most important and efficient source of water passing underground is through the Canary

pine trees - their needles trap water droplets from the cloud at around 1400 to 2000 m,

which then percolates onto the ground and through the soil. Conservation of these forests isa priority, and special reservation is made for these in the Mt. Teide National Park.

Figure 13: principal stages in formation of environment for groundwater

Tenerife is fortunate to receive around 450 mm p.a. of rainfall along its north-western flanks

due to its geographical position among the Canary Islands, and the height of the Central

Edifice, which traps condensation brought in by Trade Winds to form clouds around 1500m

altitude.

However, the quantity of non-saline groundwater in theory represents only a quarter of the

actual water which Tenerife receives as precipitation. 72% is lost via run-off into the

Atlantic, or is evaporated. The small amount of snowfall accumulating around the peak of

Mt. Teide is an important contribution to the groundwater resource, as it melts slowly,

allowing more percolation in situ (Figure 14).


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Figure 14: movement of water following rainfall upon Tenerife interior

Secondly, water not only passes vertically through the porous ignimbrite and recent

deposits, but also travels approximately in parallel with the volcano slope, and towards sea

level, where it converges with absorbed seawater. As long as fresh groundwater passing

down through the volcano is sufficient, the marine saltwater is kept separate below a

certain height under pressure induced by the overlying porous volcanic mass. Depletion and

over-exploitation of the groundwater will result in infiltration by seawater, as the growing

vacuum left behind by the extracted water draws up the seawater.

Fluvial channels throughout much of the year are entirely barren with respect to surface

water. As mentioned earlier, clay and storm deposits which still accumulate today are a

signature of the periodic events in which water cascades down narrow valleys during

occasional storms. This can occur perhaps once or twice a year. The south side of Tenerife is

very arid, being on the leeward side of the island. Occasional minor streams emerge around

the caldera, but there are no significant streams running to the sea.

3.2: Applications and Limitations

HISTORY

Before tourism became significant, its primary use was for agriculture. Even today, banana

plantations are the most profitable arable asset for the island. The Guanchos (indigenous

inhabitants of Tenerife since around the second century AD) developed the galleria system,

where water springs in gullies were, and still arc, intercepted by channels dug out of the

ignimbrite rock face (Figure 15).

The Spanish colonists since the 16th

century adopted this system which was used for

plantations, principally sugar production. Streams and waterfalls were abundant in that

time: deforestation and increasing agriculture have imposed pressures on the water supply,

causing year-round streams to be depleted. With tourism included today, there are almost

no all-year-round streams.


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Figure 15: tunnel for draining out groundwater

An additional feature to the galleria network was introduced by tapping into the

groundwater through tunnelling down to the phreatic zone. Today there are thousands of

tunnels. Throughout the 20th

century these have caused the water table to sink by around200 m - during the late 1970s, the rate of descent was around five metres each year. With

much greater demands by tourism, and an increasing population, this rate will be even

greater today.

The tunnels themselves have a limited lifetime, and must be extended rapidly to maintain

water output (approx. 70m per day). During the late 1970s the average distance was around

3 km, and the longest tunnel was 5 km. Such distances into the volcano can be detrimental

to workers due to gases and extreme heat, and so a depth is reached where further

excavation becomes inhospitable.

AGRICULTURE

Exports differ from those of colonial plantations up until the last century; sugar and wine

have been replaced by a prosperous banana industry, and also a diverse range of vegetables

such as tomatoes, cucumbers, potatoes, peppers and grapes. Ornamental plants are also a

commodity. Bananas and tomatoes form the vast majority of farming exports by mass:

Tenerife agricultural output in 1995

Export Amount sold (tonnes) Revenue (Bn pesetas)

Bananas 153,619 12.500

Tomatoes 120,000 9.054

Ornamental plants 32,907 4.023

Vineyard grapes 20,175 3.409

Around 90% ol' ail yields are exported to mainland Spain; agriculture account for 10% of

GDP on Tenerife, but this fallen from much higher proportions during the 1950s when

tourism was starting to become an important resource. The output of certain crops has

decreased in recent years; this may be due to land purchasing for new developmenls, whichare expanding rapidly. New building sites for plazas, hotels and other tourist facilities sprawl


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the fringe of Los Christianos.

In terms of water usage, agriculture, particularly banana plantations, are demanding: each

banana plant utilises 90 litres of water every day. Seen as large white rectangular sites from

the air (Figure 16), these are covered with condensation nets to recycle the water.

Figure 16: banana fields seen from distance (white patches)

TOURISM

Over 3 million visitors, predominantly of Western European origin, visit Tenerife alone each

year. The island receives almost half the number of tourists visiting the seven main Canary

islands, and at present (2001) is the most popular destination (although the Gran Canarian

influx does not fall far short).

Tenerife as a holiday destination is popular with Spanish, British, French, German andScandinavian tourists. Figure 17reflects the general (albeit imprecise) increase in numbers

during the winter months, with peaks around February and March. Many tourists are retired

citizens seeking warmer weather during this time of year. Throughout the year, Tenerife is

almost permanently dry and sunny, especially around the coast where precipitation is rare

to non-existent.

Figure 17: number of tourists visiting three of the Canary Islands during the mid-1990s


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Figure 18illustrates the dramatic decrease in agricultural employment, the opposite trend

in service industry employment, plus the emergence of a new employment sector

(construction) on Tenerife during the 1960s through the 1990s. Throughout that time, the

island population tripled, but also was also a migration of workers and foreigners to the

southern coast as hotels and facilities have been established therein. 5% of the 700,000

population are registered foreigners seeking employment in the tourist sector. As shown inFigure 17, between 200,000 and 350,000 tourists visit the island each month. In 1993,

Tenerife received 2.5 million visitors; this increased to over 3 million in 1995. Developments

are expanding rapidly around resorts including Las Americas and El Medano.

Figure 18: changes in employment sectors on Tenerife

Spanish environmental groups (such as Fundacin Encuentro) have recently criticised the

behaviour of the tourist sector's strong dominance on both the economy and Tenerife's

natural resources, especially its water requirements, for accommodation, waste treatment

and general use in businesses such as restaurants, shops and entertainments.

Water contamination and deterioration in purity is evident. Tap water is highly unsafe for

drinking as the waste treatment facilities recycle water which is returned to the water

supply network. This is not performed very carefully as the pressures of demands on water

by the growing resorts only allow for primary treatment, whereby in some cases, waste is

directly disposed into the sea. The water which is returned will contain bacterial populations

plus industrial toxins, and is treated with heavy chlorination (detectable by odour using tap-

water).

WATER OWNERSHIP

There are no water companies which administer where the water is allocated. Instead it is

owned by individual distributors farther uphill, who charge customers in terms of quantities

purchased (in "water-hours"). This is a complex system, whereby the owner of the galleria

tunnel may charge one or more distributors further downhill, before the water reaches the

customer (Figure 19). Some businesspeople have generated considerable wealth through

this process, and changes in water piping reflect conflicts over prices and between owners.

The supply may be cut off during late night hours in hotels to save money as well as wateritself.


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This autonomous system of water distribution does not allow any central authority to

monitor and impose legislation on water purity or its rate of exploitation.

Figure 19: a typical Tenerife water distribution pipeline system from source to receptors

THE IMPENDING WATER CRISIS

Many aquifers have already dried up - several old gallerias and tunnels have been

abandoned, with new pipelines linking up to new sources crossing the hillsides.

As the phrcatic zone is a feature which forms a discrete section through the volcanic cone

(Figure 14), depletion in one end affects the groundwater abundance throughout the

system. Thus the whole of Tenerife will be affected all at once by the oncoming water crisis,

probably in the next decade. Seawater drawn up will infect the water supply network - not

only is this a health hazard and a great inconvenience for the tourist industry; it is also fatal

for agriculture, which is heavily dependent on large quantities.

Predictions include the possibility that the present day demands imposed by agriculture and

tourism will induce this shortage within the next decade. New sources of water through

desalinization are already being developed in preparation- but will be brought in at a

reduced rate, at great expense. The result of the crisis could include widespread

unemployment, and a resulting migration of Tenerifians as the economy subsides,

TENERIFE: THE SITUATION IN 2015?

The agricultural sector may be the worst-affected. Individual desalinization plants elsewhere

on the Canary Islands produce would have to produce between 100,000 and a million litres

of water a day. 4200 hectares of land on Tenerife is given over to farming. Several of these

plants would have to be set up simply to meet present-day needs alone. It is likely that

significant proportions of the island's agricultural output will become unsustainable, putting

many farmers out of business.

Tourism will change significantly as facilities become scarce due to rising water prices and

closure of businesses. The rising costs will affect a majority of tourists until only moreaffluent people will be inclined to visit the island. Water rationing will become a strict


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priority, similar to resorts on the eastern Canary Islands, on Malta, and in Cyprus.

POSSIBLE ALTERNATIVE TO DESALINISATION

The diagram (Figure 20) is a simplified illustration of the series of processes required to

make seawater suitable for use not to drinking water standards). Equipment is expensive,

and the entire procedure must he performed carefully, since seawater not only is saline, butis also seriously polluted with organic compounds, inorganic chemicals and pathogens. One

solution thought of in the past was to construct large dams which would retain a portion of

the 72% of water reaching Tenerife lost as run-off, particularly on the north-west coast. Due

to the porosity of the overlying volcanic deposits however, this would prove to be inefficient

due to the lack of watertight catchment basins allowing water to escape underground. The

almost perennial non-existence of rivers and the sporadic nature of torrential rainstorms

also make the proposal appear insensible, although a water company may be able to

provide the technology and systematic approach to overcome these problems in the future.

Figure 20: a design of a desalinisation plant (sourced from ewatermark.org, 2001)

A short-term proposal may be to ship in water supplies from the continent, and elsewhere

on the Canary Islands. Hierro, less affected by tourism, and with its wetter climate further

west, may be an important source of supplies. At present, some drinking water is imported

from elsewhere on the Canary Islands to Tenerife. This may also be expensive however, andwould have to be performed in conjunction with desalinization.

CONCLUSION

Realistically, the only way of reversing the trend towards the water crisis at this stage would

be to greatly reduce the impact of development, tourism and agriculture, which would

adversely affect the economy. Ideally, the population of Tenerife should be much smaller

than at present. Neither suggestion would be popular to anyone there within the short time

left, hence the drying out of aquifers is probably now unavoidable.

Tenerife contains a unique and very sensitive environment, particularly where water is


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concerned, and the damage done to this by intensive agriculture and rapid urbanization will

soon be made known to the local population, forcing them to make difficult decisions on the

future of their economy and society.

REFERENCES

Literature

Aranco, Vicente, 1974. Los Volcanoes de las Islas Canarias(Canarian Volcanoes). Tenerife.

Pages 26-31,44-45,86-88,122-137

Consejo Superior de Cameras de Comercio, Industria y Navegacion de Espana, 1963. Atlas

Comercial de Espana, Madrid. Hoja No.38 (Mapas Provinciales). Provincia de Santa Cruz de

Tenerife

Espasa Calpa, S.A., 1998. Atlas de Espana. Canarias; pp168-170. Communidades

Autonomas

Websites (accessed February 2001; these may no longer exist)

Arona.org

http://arona.org/turismo/ingles/default.htm

eWatermark.org

http://ewatermark.org/watermark6/msg-eds.htm

hEureka.org

http://heureka.clara.net/tenerife.htm

Hoh Canarias

http://hohcanarias.com/frames/references.htm

Islas.com

http://islas.com/Tenerife/guidebook/nature

Web Tenerife

http://webtenerife.com/puntonifo/texto/GB/0169ECON/52.html
http://arona.org/turismo/ingles/default.htmhttp://arona.org/turismo/ingles/default.htmhttp://ewatermark.org/watermark6/msg-eds.htmhttp://ewatermark.org/watermark6/msg-eds.htmhttp://heureka.clara.net/tenerife.htmhttp://heureka.clara.net/tenerife.htmhttp://hohcanarias.com/frames/references.htmhttp://hohcanarias.com/frames/references.htmhttp://islas.com/Tenerife/guidebook/naturehttp://islas.com/Tenerife/guidebook/naturehttp://webtenerife.com/puntonifo/texto/GB/0169ECON/52.htmlhttp://webtenerife.com/puntonifo/texto/GB/0169ECON/52.htmlhttp://webtenerife.com/puntonifo/texto/GB/0169ECON/52.htmlhttp://islas.com/Tenerife/guidebook/naturehttp://hohcanarias.com/frames/references.htmhttp://heureka.clara.net/tenerife.htmhttp://ewatermark.org/watermark6/msg-eds.htmhttp://arona.org/turismo/ingles/default.htm


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APPENDICES Plate A


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APPENDICES Plate B


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APPENDICES Plate C


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APPENDICES Plate D

Documents

Tenerife: formation, stratigraphy and water resources