ABSTRACTS / RESUMES - Comitato Glaciologico Italiano

XAVIER UBEDA, LOURDES REINA & MARIA SALA
Rill development as a consequence of changes
in hydrology after forest fires
Departamento de Geografia Fisica, Universitat de Barcelona,
Facultad Geografia i H". Baldiri Reixac sin, 08028 Barcelona, Spain
The research has been carried out in a forest located in the
Cadiretes mountains, which burnt on 7 th of July 1994 in
Llagostera, Girona province, NE Spain. The fire affected
12.66 hectares of a Pinus pinaster and Quercus suber forest.
The average rainfall in the area is 675 mm/year, with a
maximum in rainfall and rainfall intensity in Autumn.
Changes in hydrology is one of the first consequence in
burnt soils. On one hand, the unprotection of soil by vegetation
and organic matter make difficult the infiltration of
all the rainfall, due to water arrives at the surface with too
intensity, and on other hand the hydrophobic response of
ashes decrease infiltration capacity. The infiltration capacity
of the soil, measured by simple rings, was even 6 times
lower in the burnt soil than in the control one. The runoff
coefficient was determined by means of runoff and rainfall.
The runoff was collected in gerlach traps, and the rainfall
was measured by a simple rain-gauge. In the first months,
the runoff coefficient was until 9 times higher in the burnt
areas than in the control unburnt zones. The runoff generated
on the slopes arrives concentrated at the forest ways
with enough power to develop rills and gullies. The rill development
is not a continous phenomenon, only when the
rainfall and rainfall intensity is strong enough, the water
erode the ways and even cause slump movements in the
borders. The total material eroded in the tracks in the
study period has been measured by the determination of
the volume of the rills and gullies.
GENNADY F. UFIMTSEV
Symmetry of the Earth planetary relief
Institute of Earth Crust, Siberian Branch of Russian Academy
of Sciences, 664033 Irkutsk, Russia
Latitudinal belts of relief of Nothern and Southern hemispheres
are antisymmetric to each other: Laurasia and
Southern ocean, Arctic basin and Antarctic continent. In
polar regions of the Nothern continental and Southern
oceanic hemispheres are situated central elements - inclusions
alien to them. Intersecting alien elements - North
Atlantic basin with Greenland and the Andes with Scotia
sea region - connect the central inclusions with allied relief
of contrary hemispheres. General antisymmetry of relief of
the Southern and Northern hemispheres is added by antianaloguous
forms: belts of great continental plains of Laurasia
and median-oceanic ridges of Southern ocean, Centralasian
belt of ridges in strip of tectonic lithosphere clustering
and EastAfrican rift belt. Antisymmetry of hemispheres'
relief conforms to pear-shaped geoid figure: uplifts of
geoid surface conform to oceanic belts, but its lows according
to spheroid - to continental belts.
Laurasia relief has a concentric-radial structure and symmetry
of cone (ooPLoo) , pointing out an expansion and stability
of this continental massif. Especial plane of symmetry
near 120 e.l. characterizes the extance of homologic
forms on east and west: Ordos and Colorado plateaus;
Fenwey and Rio-Grande rifts; Mongolia-Siberian and
Verkhoyan-Kolymian mountain belts; the Urals and Appalachian
mountains. On the east of Asia disturbance of symmetry
of cone: young mountain are changed by island arcs;
on peripheries of basins of marginal seas there are formed
mountains of destructive types.
Southern continents and subcontinents-fragments of
Gondwanaland have similar forms and are characterized
by latitudinal translations and translations of similarity.
Positions of southern continents and meridional harts of
mid-oceanic ridges of Southern ocean are characterized by
symmetry axis of fourth order L4 with disturbance of this
symmetry in .Western Pacific, where Darwin underwater
uplift and belt of backarc riftogenesis and marginal seas'
spreading are situated. Equatorial belt of sinistral oroclines
consists of horizontal curves of mid-oceanic ridgesia);
concavaltb) and convexlc) borders edge of the gondwanaland
continents, island arcstd) and aseismic ridgesle), Leading
with Eastern Pacific uplift and to the east it is the
combination (abcl-Iabcl-abcl-Ide}, Structure of (abc)
group is characterized by three-divisible antitranslations,
and of (de) group - two-divisible antitranslations, and of
(de) group - two-divisible antitranslations, but position of
these groups on Earth - is characterised by symmetry axis
of fourth order L4 with disturbance of symmetry in Western
Pacific, where (abc) group is changed by (de) group
and the belt of equatorial sinistral oroclines is abruptly
extended.
Co-ordination of planetary relief structure with geoid figure
and tectonosphere structure (saturation of the Southern
hemisphere by asthenosphere layers and lenses) is a foundation
for hypothesis of anisotropically expansing-compressing
postgondwanian Earth. Tectonosphere of planet
is expanded in the Southern hemisphere and is relativelly
compressed in the Northern one, but change of linear
speed of rotation in equatorial belt stipulates a formation
of sinistral curves of forms of planetary relief. Due to rotative
processes occurs smoothing of planet figure and displacing
of tectonosphere matter (firstly continental massives)
to the north.
Disturbance of planetary relief symmetry and availability
of high uplift of geoid surface in Western Pacifies point
out that in this part main transformation in tectonosphere
and on Earth surface takes place.
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