411where the international standard is a synthetic metal from
the Institute for Reference Material and Measurement
(i.e. IRMM-014). It provides the deviation of the isotope
ratio of a sample relative to the standard, with a permil
unit (‰).
Iron isotope fractionation variations of the iron isotope
distribution between two different chemical species; for
instance dissolved ferrous Fe and a solid precipitate.
Isopach map map of the equal thickness of the deposits. It
is necessary to determine the energy of the eruption, its
volume and the plume height.
Jointed basalt Jointing is frequently shown by lava flows
when they are cut by erosion or in a quarry as a series of
parallel columns several meters high and a few decimeters
in diameter. The jointing results from shrinkage (decrease
in volume) at the end of lava cooling, when lava changes
eventually from a semi-liquid state to a totally solid state.
Juvenile pyroclast in volcanic deposits, they consist of par-
ticles made of the magma erupting.
k-strategist species (k-strategist) In ecology, r/K selection
theory relates to the selection of combinations of traits in
an organism that trade off between quantity and quality
of offspring. K-selected species are described as “equi-
librium” whereas r-selected species are referred to as
“opportunistic”.
L* parameter a specific spectrophotometric parameter pro-
viding the brightness of sediment.
LMGE Laboratoire Microorganismes: Génome et
Environnement (LMGE, CNRS/Université Blaise Pascal
Clermont-Ferrand 2).
Lahar mudflow of volcanic origin.
Lake cult most maar-lakes had specific lake cults in pre
or early Christian times, generally with peculiar pagan
(Mephites, Diana, Jupiter) or Christian (StMichael, Holy
Virgin) deities.
Lake degassing emission of dissolved gases contained in
lake deep waters, generally CO 2 , sometimes with H 2 S and
CH 4. Intensity range from light bubbling to water foun-
tain, limnic erution, overspills. It can be a permanent state
or sudden events. Many degassing events described since
2400 years in maar-lakes remained unknown to modern
scientists until 2000s.
Lake overspill rise of lake water levels due to increasing
dissolved gas content, then overspill above the lake rim.
The Albano Lake catastrophic event (398 BC) that threat-
ened Rome has been the first to be demonstrated by Earth
scientists in the 2000s; it was well known by ancient
Rome historians and described as a major prodigium.
Lava a general term for a molten extrusive volcanic forma-
tion and also for the rock that is solidified from it.
Leaching The action to drain away from soil, ash, or simi-
lar material by the action of percolating liquid, especially
rainwater.
Limnic eruption sudden violent explosion of lake surface
waters due to deep water degassing, often catastrophic
to nearby populations. Although Lake Nyos event (1986,
1700 victims) is the first being analysed by modern scien-
tists, the Lake Monoun explosion occurred before in 1984.
Limnogeology the branch of geology that deals with lakes
aiming at reconstructing continental environmental
changes through geological times, based on a multidis-
ciplinary study of fossil or recent lacustrine sedimentary
systems.
Limnology the scientific study of the physical, chemical,
meteorological, biological and ecological conditions and
characteristics of all inland waters.
Lineament a linear, topographic feature of regional extent
that is believed to reflect a tectonic feature due to crust
deformation.
Lorica Shell-like protective outer covering, often reinforced
with sand grains and other particles that some protozoans
and loricifera metazoans secrete. Usually it is tubular or
conical in shape.
Lysogeny Replication cycle in which temperate bacterio-
phage integrates its nucleic acid into a host genome. Thus,
the newly integrated genetic material may be transmitted
to daughter cells at each subsequent cell division without
viral particles production and host cell lysis.
Maar-lake lake located in an explosive volcanic crater
(maar), often with steep clifs and generally without river
input or outlet.
Maar German word, which initially points to the circular
lakes in the Eifel area located in Rhineland (Rhénanie).
Crater of explosion, generally showing a large diameter,
occupied by a lake or filled by sediment, and that has cut
out the pre-existing basement. The fragments extracted
from the basement always represent a noticeable, often
prevailing percentage of expelled products. The maar
contains two elements:- The crater, a circular depression with steep walls, the
diameter of which varies between 100 m and 2 km, and
profoundly rooted in the basement (generally approxi-
mately 1000 m). It can be occupied by a lake, a wet zone,
an accumulation of lava, a cone of scoriae, or by a lava
flow stemming from a neighbouring volcano. - The projections form a ring or low-relief crescent. The
stratified deposits contain a large proportion of angular
fragments scoured from the basement. The magma of the
eruption (juvenile magma) is represented by dense clasts
and heavy bombs termed “cauliflower bombs” due to
their varicose surface.
A maar forms when the ascending magma meets en route
surfacial water, groundwater or a stream. The instanta-
neous evaporation of this water fuels a very explosiveGlossary