ABSTRACTS / RESUMES - Comitato Glaciologico Italiano

ment gestionnaire des indispensables outillages d' enregistrement
et de rassemblement des donnees ondametriques
entrainernent non seulement des engagements de personnel
et economiques de plus en plus onereux, mais surtout
demandent d' engager un convenable intervalle temporel
pour acquerir les donnees.
Afin donc de gagner du temps on a prevoit une methode
rapide de calcul pour n'importe quelle plage italienne des
valeurs ondametriques au brisant en utilisant les cartes isobares
bijournalieres (12 Ute e 00 Ute) du Deutscher Wetterdienst
relatives au Meditcrranee. On a fait la digitalisation
des ces cartes pour la periode 1984-1995 rapportant
les isobares a un reseau avec des mailles de 120 km de
cote, dont les sommets presentent coordonnees geographiques
connues. Dans ces sommets on a determine pour chaque
carte le gradient de pression et le vent geostrophique
dont on a obtenu le vent (direction, vitesse, duree) ala surface
de la mer.
Avec un precede mathematique de B-Spline methods en appliquant
les curves et surfaces de Bezier on a pu, pour chaque
carte, determiner les relatives spline functions.
C'est aussi qu'on peut alors determiner, pour n'importe quel
point de la surface marine, les precites parametres du vent.
Pour une plage choisi on peut aussi calculer, dans un point
predestine en haute mer, les caracteristiques du vent a la
surface (direction, vitesse, duree) et done, avec les coordonnees
azimutales des differents secteurs et la longueur des
fetches, le relatif climat houleux. Avec la connaissance de
ces caracteres ondametriques en haute mer de la plage, on a
realise un programme pour determiner, dans la zone de brisant
de la meme plage, l'hauteur et la periode de la houle
d' ou en consequence la determination des parametres
morphodynamiques surf scaling de Guza & Inman (1975) et
environment parameter de Dalrymple & Thompson (1977).
L'application de cette methode aquelque exemple des plages
italiennes fournit des bons resultats sur leur etat
morphodynamique.
MICHAEL CROZIER & THOMAS GLADE
Magnitude and frequency of landslide events in
New Zealand
Department of Geography, Research School of Earth Sciences,
Victoria University, p.o. box 600, Wellington, New Zealand
Landslide activity in New Zealand constitutes a significant
natural hazard and an important geomorphological process.
Questions of frequency and magnitude of events are
therefore fundamental for social and economic planning as
well as understanding landforming processes.
Magnitude of landslide events can be represented by measures
of mass, volume (eg; total volume displaced per
event), or measures of degree-of-presence (eg: number of
landslides per unit area, or area affected). Frequency can
be represented temporally by mean return periods for
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events and spatially by density (number of landslides per
unit area). Temporal frequency can be determined either
form the actual landslide record or by establishing the
landsliding threshold of the triggering agent and determining
the probability of occurrence of the threshold value.
Thresholds are most usefully defined in terms of a given
magnitude of sliding but in most cases there is insufficient
information available to represent magnitude. Thus, reported
thresholds and frequency may refer simply to event occurrence
(without any reference to their magnitude), or to
specific magnitudes of landsliding.
Because of the variability of inherent and triggering stability
conditions, thresholds established from the triggering
agent tend to be represented by a band of probable triggering
values, rather than a definitive envelope. In this case,
it has become practice to recognise a minimum triggering
threshold below which no landsliding occurs and a maximum
threshold above which all triggering values produce
landslides, separated by a band of increasing probability of
occurrence towards the maximum threshold.
Observations indicate that, even over the period of a few
years, threshold values may shift in value, particularly in
areas subject to recurring landslide events.
Magnitude/frequency analysis may also be applied spatially
to the population of landslides occurring in one event.
Concepts of geomorphic work and geomorphic effectiveness
of landsliding events may also be approached through
magnitude/frequency analysis. Calculation of the transient
form ratio (recurrence interval/relaxation time) enables an
assessment of the persistence of landslide impact and the
identification of landsliding as a major terrain forming process
in parts of New Zealand.
HERVE CUBIZOLLE 1 & BERNARD VALADAS2
Holocene evolution ofa fluvial valley in the
crystalline mountain:
the Dore valley in the French Massif Central. First results
1 Universite Jean Monnet, Umr Cnrs 5600, 6 rue Basse des Rives,
42023 St-Etienne, France
2 Universite Blaise Pascal, Upres-a Cnrs 1562,
29 Boulevard Gergovia, 63037 Clermont-Fd., France
The purpose of our research is to describe and explain the
holocene evolution of the Dore valley. We have begun to
reconstruct 8000 years of interaction beetween people and
nature as part of paleo-environemental approach which
appeal to geomorphological, archaeological, historical and
palynological data. This paper summarises the first results
of our investigations.
The Dore is a meandering river of the French Massif Central.
The catchment (1716 km') is 80 % in granites and metamorphic
rocks and only 20 % in Cainozoic sedimentary
rocks (argillaceous and sandy rocks). These are the lowlands
«600m) of the Arlanc and Limagne plains where the
studied valley sections are located.