Model help:Gc2d

Gc2d

GC2D simulates glacier evolution. The component simulates the formation and evolution of temperate valley glaciers or ice sheets on a two-dimensional topographic surface as driven by a specified meteorological setting. It is presently coupled to TOPOFLOW to investigate glacio-hydrological interactions.

Model introduction

gc2d is a two-dimensional finite difference numerical model that is driven by a calculations of glacier mass balance (snow precipitation - melt rate). The model calculates ice surface elevations above a two-dimensional terrain by solving equations for ice flux and mass conservation using explicit methods.
The present component is a simplified version of the original Gc2d model, it focuses on the interaction with a hydrological model, and thus generates meltwater to a river system.
gc2d integrates glacier and climate simulation components explicitly, and thus has the unique ability to simulate feedbacks between the changing ice surface and the climate forcing.
The efficiency of this model allows simulation of glacial evolution over millennial timescales at spatial scales that resolve valley glaciers. Finally, from a computational standpoint, the simplicity of this model permits the investigation of significant regions of parameter space, allowing us to determine the effect of new processes or altered algorithms for them.

Model parameters

Input 1

Input 2

Input 3

Toggles

Output

Parameter	Description	Unit
Component Status	Defines whether this component is used in the specific coupling	Disabled/Enabled
Input Directory	Defines the input directory for the simulation, it should contain a DEM file	-
Output Directory	Defines the output directory for all files requested under the output tab	-
Site prefix	Identifies simulations for a specific location, do not change if using example bld files	-
Case prefix	Identifies distinct simulations for the same region	-
Number of steps	The total number of steps for the simulatiom	-
Timestep	Internal time step for the glacier processes	years
Max time step	Maximum stable internal time step for the glacier processes	years
Max simulation time	Maximum total simulation time	years

Parameter	Description	Unit
DEM file	binary file containing topography	m
Init Ice Depth file	binary file containing initial ice thickness data	m

Parameter	Description	Unit
First parameter	Description parameter	[Units]

Parameter	Description	Unit
First parameter	Description parameter	[Units]

Parameter	Description	Unit
First parameter	Description parameter	[Units]

Uses ports

This will be something that the CSDMS facility will add

Provides ports

This will be something that the CSDMS facility will add

Main equations

Basic Process Relationships
Ice is transported between grid cells via ice deformation and basal sliding. Glen’s Flow Law, describes ice deformation, U, vertically averaged:

U = 2/5 A * hi * (tau_b)ⁿ

A = coefficient of Glen’s Flow Law (Paterson, 1994).
A = 2.1 E^-16 Pa^-3/yr, this is the Arrhenius constant (MacGregor, 2000).
hi= ice thickness (m)

Basal sliding velocity, Us (m/yr)

Us=Uc e^(1-(tc/tb))

Uc = characteristic sliding velocity (m/yr)
tc = gravitational driving stress (Pa)
Typically in temperate glaciers sliding velocities vary from 0-30m/yr. tb and tc have a narrow range around 0.5-1.5 or 1 bar = 10⁵Pa.

Mass Balance Parameters
A ‘mass balance’ of a glacier tracks the changes in the mass of a glacier, and the distribution of changes in space and time. A mass balance then is the sum of accumulation and ablation.
Accumulation: all processes by which mass is added. Most input comes through snow, but other accumulation occurs through avalanches, rime and refreezing of rain. Ablation: all processes that cause mass loss. Melting and runoff of the meltwater, evaporation, snow erosion due to wind. A glacier has two distinct zones. The upper section of the glacier that receives the most snowfall over a year and experiences no net melt is called the accumulation zone. Rule of thumb is that this makes up 60 – 70% of the total surface area of a stable glacier. The lower end of the glacier is known as the ablation zone where more ice is lost from melt than gained from snow fall. The altitude separating the two zones is called the equilibrium line altitude, ELA:
ELA = equilibrium line altitude (m)
In GC2D, the initial elevation of the ELA is specified at a certain elevation contour (in m), it can subsequently change with changing climate.

Notes

Since GC2D is a 2D model it uses an initial topographic surface (a DEM=digital elevation model).
Presently, GC2D has been coupled to TopoFlow, so it needs to work with a similar DEM and flow grids as TOPOFLOW. For TOPOFLOW, these DEM’s and associated files are based on Rivertools-DEM’s (‘rtg-files) and their associated Header files (‘rti-files’). For GC2D in stand-alone mode, the format of the DEM can be just a binary-file.
Similary, an ice thickness grid can be overlayed on top of the DEM if one wants to initialize the simulation with an existing ice topography. This ice thickness file is also a binary file.

Numerical scheme

Examples

An example run with input parameters, BLD files, as well as a figure / movie of the output

Follow the next steps to include images / movies of simulations:

• Upload file: http://csdms.colorado.edu/wiki/Special:Upload
• Create link to the file on your page: [[Image:<file name>]].

See also: Help:Images or Help:Movies

Developer(s)

Original development was done by Mark Kessler, the component in the CMT as of November 2010, is a simplified Python version (called Gc2dV0) as revised by Scott Peckham.

References

• Paterson, W.S.B., 1994. The Physics of Glaciers. 3rd edition. Elsevier Science, UK.

• MacGregor, K.R., Anderson, R.S., Anderson, S.P., Waddington, E.D., 2000. Numerical Simulations of Glacial-Valley Longitudinal Profile Evolution. Geology, 28, 11,1031-1034, doi:10.1130/0091-7613(2001)029%3C0760:%3E2.0.CO;2.

• Kessler, M.A., R.S. Anderson, and G.S. Stock, 2006. Modeling topographic and climatic control of east-west asymmetry in Sierra Nevada Glacier length during the Last Glacial Maximum, J. Geophys. Res., 111, F2, F02002, doi:10.1029/2005JF000365.

• Kessler, M.A., Anderson, R.S., Briner, J.P. 2008. Fjord insertion into continental margins driven by topographic steering of ice. Nature Geoscience 1, 365-369 (11 May 2008) doi:10.1038/ngeo201 Letter

Links

Link to the model metadata as submitted by the original developer:
Gc2d model metadata