Impaginato Baioni


DDRRAAIINNAAGGEE  NNEETTWWOORRKK  AANNDD  EENNEERRGGYY  RREELLIIEEFF
OOFF  MMAADDEEIIRRAA  IISSLLAANNDD  ((PPOORRTTUUGGAALL))::

PPRREELLIIMMIINNAARRYY  NNOOTTEESS

DDaavviiddee  BBaaiioonnii11,,    DDoommiinnggooss  RRooddrriigguueess22 &&  GGiiuulliiaannoo  GGaalllleerriinnii11
1Università degli Studi di Urbino,Campus Scientifico, 

Istituto di Dinamica Ambientale  Loc. Crocicchia, 61029 Italy.
2C.C.B.G. - Universidade da Madeira,Campus da Penteada, 9000 Funchal, Portugal. 

ABSTRACT
A geomorphological study, integrated with satellite imagery analysis, has been carried out in the Madeira Island to identify the influence
of neotectonics on the landscape. Drainage network and energy relief are the main geomorphological indexes used to identify recent
uplift. The drainage anomalies and areas of high relief energy, often coincident, are not explainable by means of the local meteoclimatic
conditions. Some peculiar anomalies, such as hook-like shapes and torsions of the network, distributed on lineaments that coincides
with those detectable from satellite images, indicate a differential direction of central block, symptom of a prevailing tectonics of uplift
with a probable horizontal component.  

RIASSUNTO
Reticolato idrografico ed energia del rilievo dell’Isola Medeira (Portogallo): note preliminari. E’ stato affrontato uno studio geomorfologi-
co preliminare integrato con analisi di immagini da satellite nell’isola di Madeira per valutare l’influenza della neotettonica sulla morfolo-
gia. I principali indicatori per identificare il recente sollevamento si sono rivelati il reticolo idrografico e l’energia del rilievo. Le anomalie
del drenaggio e le aree ad alta energia del rilievo sono spesso coincidenti e sembrano non essere condizionate dalle condizioni meteo-
climatiche dell’isola e risultano essere in relazione ad alcune lineazioni tettoniche evidenziate nelle immagini da satellite. Tale situazio-
ne morfologica indica un sollevamento differenziale del blocco centrale con una probabile componente orizzontale.  

Keywords: Drainage network, Energy relief,  Neotectonics, Madeira Island.

Parole chiave: Reticolo di drenaggio, Energia del rilievo, Neotettonica, Madeira

Il Quaternario
Italian Journal of Quaternary Sciences
1155(2), 2002, 271-274

11  IINNTTRROODDUUCCTTIIOONN

A stream channel network analysis has been car-
ried out on the existing cartography available at the
1:50.000 scale (I.G.A. Madeira, cf. table attached). On
the basis of the detected patterns, network anomalies,
that were not justifiable by means of terrain lithology and
structural tectonics, were identified. Concurrently, the
map of relief energy was derived so that further morpho-
tectonic information via an integrated analysis could be
obtained.

22  GGEEOOLLOOGGIICCAALL  AANNDD  GGEEOOMMOORRPPHHOOLLOOGGIICCAALL
SSEETTTTIINNGG

Madeira Island is located in the North Atlantic,
900 Km southeast of Lisbon. It has an area of 728 Km2

and 265000 inhabitants. It is of volcanic origin, Miocene
period, and considered as the present location of a hot-
spot that also originated the Desertas Islands (which
belong to the same volcanic complex), Porto Santo
Island and the seamounts Seine, Unicorn, Ampere,
Coral Patch and Ormond.  Madeira has in its central
region swarms of vertical dikes, normal faults, graben
structures and cinder cones, parallel to the long axes of
Madeira (EW) an area characteristic of volcanic rift

zones (Biancotti, 2001; Geldmacher & Hoernle, 2000).
Lithostratigraphically the geology of Madeira Island can
be divided into three units. The first, a basal unit, was
formed during the late Miocene to Pliocene and is
mainly formed by volcanic breccias and pyroclastic
deposits. The second, the middle unit, is composed by
basaltic lava flows and formed from the Pliocene to the
Pleistocene. The third, the upper unit, consists of scoria
cones and intra-canyon lava flows formed during the
renewed volcanic stage of evolution of the island
(Geldmacher & Hoernle, 2000). 

The orography is characterized by a strong relief
with altitudes that reach 1860 m, the average altitude is
of 700 m. Average rainfall values vary from 600 mm in
the southern coast to 3000 mm in the areas of high alti-
tude.

The lithology and the structure of the volcanic
body, which originated the island itself, mainly influence
the morphology of Madeira Island. Climatic changes, the
last periods of quaternary volcanic activity (Mata, 1996),
neotectonics and sea level variations have played an
important role in the definition of the morphological con-
figuration. In addition, intensive anthropic impacts,
essentially concentrated on coastal areas, have caused
further changes to the landscape. The most active pro-
cesses are coastal erosion (the northern shore faces NE
and N winds, hence it is affected by active marine ero-



272 D. Baioni, D. Rodrigues & G. Gallerini

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273Drainage network and energy relief ...

sion whereas the southern shore results to be more pro-
tected), run off erosion and chemical weathering of
pyroclastic lithologies. The drainage network is heavily
incised and vertical erosion dominates.

22..11  DDrraaiinnaaggee  nneettwwoorrkk  aannaallyyssiiss
The study of the drainage network (fig.1) indicates

at least 2 main patterns, parallel diverging and dendritic
ones, and reveals that generally the existing basins are
distributed in a centrifugal manner around the central
relief. The Ribera de Janela basin represents an excep-
tion; it develops by overlapping in an anomalous way
transversally to the dominant drainage direction. It is
likely that such a basin represents a more recent forma-
tion compared to the surrounding drainage system. A
significantly diverging drainage pattern extends in the
area south of the main divide, between P.ta do Sol and
P.to Moniz (WNW part), in the area between Funchal
and Machico (SSE part) and in the area north of the
main divide between the Arch of St. Gorge and Faial.
Diverging nets are typically derived from previous allu-
vial fans and/or pediment surfaces (cfr. Nesci & Savelli,
2001). Where it is found, diverging drainage developed
independently both from the geological and structural
setting and from the age of terrain. Sometimes together
with diverging patterns a parallel net prevail, especially
in the SW coast sector of the island. Parallel streams in
this diverging net could be derived from the ancient
topographic configuration on a more pronounced slope.
A dendritic-feathered pattern prevails in the central part
of the island, it generally develops on rocks of uniform
sedimentary units. This pattern shows a very high drai-

nage density. Anthropic modifications affected the chan-
nel network around densely populated and intensively
cultivated coastal areas.

A detailed analysis has allowed the identification
of network branches characterised by an anomalous
pattern (torsions, elbow-like, rectilinear and barbed seg-
ments). The occurrences of such anomalous branches,
that can be correlated to lineaments (Fig.1, Fig.2), have
been interpreted as tectonic constraint of the network. In
fact, they are not justifiable by other causes (selective
erosion, slope gradients, anthropogenic factors, etc.).
This is also confirmed by the exceptional corresponden-
ce that exists between the majority of the lineaments
and those detectable from satellite image interpretation
(cf. Fonseca & alii,1998 a and b)

22..22  RReelliieeff  eenneerrggyy  aannaallyyssiiss
The relief energy analysis has been conducted by

extraction of an energy map. Topographic maps
(1:50.000 scale) of the Madeira Island have been divi-
ded into 2 by 2 cm. squares (equivalent to a linear scale
of 1.000 m on the ground)  (cfr. Klein & Antun, 1983).
Subsequently the squares have been numbered accor-
ding to an orthogonal co-ordinate system. For every
square minimum and maximum elevation have been
estimated using contour lines as references (equidistan-
ce equals 25 metres).  The relief energy has been obtai-
ned by subtracting the minimum from the maximum
value. The obtained map presents two areas of high
relief energy. One extends essentially on the central
region of the island, occupied by the central massif, the
other is located in the northern part between P.to Moniz

Fig.2 - Spot image of Madeira Island (Project Corine Land Cover Ilha da Madeira.CNIG. Secretaria Regional do Equipamento
Social.Governo Regional da  Madeira)

Immagine da satellite dell'isola di Madeira (Project Corine Land Cover Il ha da Madeira.CNIG. Secretaria Regional do Equipamento
Social.Governo Regional da  Madeira)



274

and P.ta Delgata, where values are certainly enhanced
by the ongoing erosion due to its peculiar exposition. To
highlight the spatial similarities among all high relief
energy areas and the high drainage density, all the most
significant anomalies of the drainage network are con-
centrated in these high relief energy areas. 

33  CCOONNCCLLUUSSIIOONNSS

This study aimed at highlighting the presence of
some landscape anomalies in specific areas of Madeira
Island. These areas are separated by main lineaments
that are easily detectable from satellite imagery (fig. 2). 

The diverging/parallel pattern, that corresponds to
low energy relief zones, indicates the presence of a
palaeo-landscape that has been partially reshaped by
erosive processes only in the south and north-east parts
of the island. When compared to others, these sectors
seem to have been subjected to a minor uplift. In contra-
st, the central part of the island shows a dendritic drai-
nage pattern with high drainage density and many ano-
malous tracts of the rivers (captures elbows, torsions,
barbed rivers, etc.). This generally indicates drainage in
evolution. Anomalous trend of the divides shows strong
headwater regressive erosion with a clear tendency to
hillslope retreats. The high-energy relief is found just in
this sector, even though in places (e.g. coastal area)
such a situation can result from the high denudation rate
of the northerly facing basins. The north-west part of the
island is characterised by the anomalous basin of
Ribera de Janela river elongated in NWSE direction.
The shape of this basin that shows a very low energy
relief probably represents the response of this mountain
sector to a very recent evolution. This assumption is
justified by the anomalous length of the stream when
compared to all rivers of the island and by the incomple-
te erosion of the palaeosurfaces of Plan De Serra,
which is most likely, a remnant of ancient landscape. In
conclusion, we identify several areas that present a dif-
ferent tectonic behaviour by means of the geomorpholo-
gical analyses reported above. In particular, the central
area appears to be the most affected by dynamics of
uplifting whereas lateral areas seem to be substantially
stable or however interested by minor uplifting. Torsions
of the stream channels in correspondence of the two
principal NWSE lineaments, might be due to different
horizontal components: clock-wise movements in the
southern portion and anti clock-wise movements in the
northern one.

AAcckknnoowwlleeddggeemmeennttss

Our thanks to Prof. O. Nesci for useful discussions.

RREEFFEERREENNCCEESS

Carvalho A.M.G. & Brandao J.M. (1991) - Geologia do
Arquipelago da Madeira. Museu Nactional de
Historia Natural (Univ.Lisboa), pp. 170.

Fonseca P.E., Mata J. & Domingos R.(1998a) -
Preliminary data on tectonic lineaments from
Madeira Island. GEOlogos - revista do Dept.de
Geol.da Fac.de Cien.da Univ.do Porto 2, 89-90

Fonseca P.E., Mata J.& Munha J.(1998b) - Tectonic
lineaments from Madeira island evidenced from
satellite image analysis and preliminary geological
data. Actas do V Congresso Nactional do
Geologia, Lisboa Comun.Inst.Geol.Min., 84(1),
101-104.

Geldmacher, J. & Hoernle, K., (2000). The 72 Ma geo-
chemical evolution of the Madeira hotspot (eastern
North Atlantic): Recycling of Palaeozoic (£ 500
Ma) oceanic crust. Earth Planet. Sci. Lett. 183,.
73¯92. 

Klein V. & Antun S. (1983) - A morphostructural analysis
of the Adriatic seabed relief energy on the basin of
a bathymetrical map on the scale 1:750.000.
Bulletin of the Inqua Neotectonics Commission,
6,40.

Mata J. (1996) - Petrologia e geoquimica das lavas da
Ilha da Madeira:implicacoes para os modelos de
evolucao mantelica.Tese de doutoramento
(Univ.Lisboa), pp. 471

Nesci O. & Savelli D. (2001) - Diverging drainage in the
Umbria-Marche Apennines  (Central Italy).
Convegno "Uplift and erosion: driving processes
and resulting landforms: dynamic relations
between crustal and surficial processes",
September 20 and 21, Certosa di Pontignano
(Siena). (Abstract)

D. Baioni, D. Rodrigues & G. Gallerini

Ms. ricevuto il 20 ottobre 2002
Testo definitivo ricevuto il 4 febbraio 2003

Ms. received: October 20, 2002
Final text received: February 4, 2003