Lecture 1 - Glacier systems and Mass balance Flashcards
Benn and Lehmkuhl (2000)
ELA’s
BR, AAR, MELM, THAR, TSAM, ELAs calculation methods
debris
Benn and Lehmkhul (2000) ELAS
ELA = the position where, over the years the accumulation equals the ablation - the average altitude
ELA reconstruction not the same in high mountainous regions vs. low relief environments
approx. linear MB gradients for simple glaciers
high mountain Gs non linear mass balance gradients; avalanching, debris and topography
ELA close link to climate (precipitation and temps) –> indicator how how a glacier responds to climate change and reconstruction
ELA effected by local factors; topo shading, supraG debris patches, preferential snow accumulations and lee-side locations
Benn and Lehmkhul (2000) debris cover
strong influence of debris on MB
thick = (>2cm) insulation
thin = lower albedo so high absorption of global radiation
Many Gs dependent on source type and debris cover e.g. firn trough glacier
Benn and Lehmkhul (2000) mass balance an ELA calculations
Balance ration (BR), Accumulation area ratio (AAR), maximum elevation of lateral moraines (MELM), toe-to-headwall ratios (THAR) cirque altitudes and the to-to-summit altitude method (TSAM) ELAs calculation methods
only BR makes explicit reference to G MB
BRs lowest in polar regions (ablation weakly depended on altitude), highest in tropical (high ablation throughout the year)
Hock (2005)
modelling
atmosphere interactions
melt
Hock (2005) modelling
modeling of ice and snow melt is important for water resource management
ice and snow major control over earth climate and hydrology dynamics
melt models vary: energy balance models and temperature index models
relationship between glaciers and climate is a critical issue
Hock (2005) atmosphere interactions
G melt determined by the energy balance at the glacier atmosphere interface - controls by meteorological conditions and the physical G properties
complex glacier - atmosphere supplied energy for the melt, while atmospheric conditions are modified by the presence of snow and ice
strong temp gradients in air immediately above the G; in melt season air is stratified and surpasses turbulence
temp stratification + typical glacier surface slopes induce gravity flows
topo can effect diffuse radiation (e.g. sky may be obscured by topo or enhanced by reflection off adjacent slopes)
empirical relationship between melt and air temp
Hock (2005) melt
surface temperature of melting can’t exceed 0dc
snow has higher albedo than ice/lower thermal conductivity –> good thermal insulator
G albedo variation determines spatial and temporal distributions of meltwater production
melt (at 0dc) is determined by the surface energy balance which is only indirectly affected by the air
most energy used for melt is supplied by radiation followed by sensible heat flux
summer snowfall can reduce melt and run off abruptly due to enhanced albedo
sublimation important at high latitudes and high altitudes
Jacob et al (2012)
total contributions to sea level rise from all ice covered regions ~1.5mm/yr
(from GRACE derived satellite gravity fields)
Nakawo and Young (1982)
debris dark colour = lower albedo
when the thermal resistance of the debris layer is known - ablation under a debris layer can be estimated from meteorological variables
Braithwaite (2002)
stake and snowsuit measurements should be more integrated with geodetic and remote sensing methods
G MB vital link between changing atmospheric environment and glacier dynamics and hydrology
changing G mass linked with changes in ocean mass
G meltwater = resource for HEP but also a hazard (e.g. unexpected floods)
Chen et al (2013)
changes in global means sea level due to 3 factors:
- water mass changes in oceans
- water density changes (-temp?)
- variations in volume of ocean basins
mass change in ocean mass due to melting of polar ice sheet and mountain glaciers
Radic and Hock (2011)
contribution to sea level rise from mountain glaciers and ice caps has grown over the past decades
important component of eustatic sea level rise
but the Antarctic and Greenland ice sheers holds considerable more water
