Report on Ice Thickness Measurements, Wilkes Land 1965/66

A report on the ice thickness measurements taken during the 1965/66 season on Wilkes Land. The work was done in three parts - an autumn and spring traverse, and a trip to S2. Includes notes on method, and some results. The document has been scanned and is available as a pdf file in the dataset download.The document contains the following sections:1) The Autumn Traverse2) S2 Trail Marking Trip3) Spring Traverse4) Spring Traverse LogisticsTaken from the "Autumn Traverse" section of the document:The Autumn Traverse (16/3/65 - 27/4/65) was a combination of glaciological and geophysical work. The course followed was a triangle with corners at Cape Folger, Cape Poinsett, and the Dome Centre situated approximately 25 miles south east of S2. The triangle had been staked in the 1964/65 season.The geophysical programme consisted of measuring ice thickness around the triangle by seismic methods and observing the earth's vertical magnetic intensity at selected points. Seismic reflection stations were installed every 10 miles. The station at Cape Folger was not installed in the autumn due to crevasse problems, but was done on 8/12/65 during a three day trip using Weasels. Including the station at Cape Folger 18 seismic reflection stations were installed on the triangle with good bedrock reflections being recorded at each station. In addition to obtaining bedrock reflections, shallow refraction shots were fired at every station to determine surface velocity profiles from the coast to the Dome centre. It was found that surface ice velocities, say, down to a depth of 200 feet, decrease from the coast inland. This is associated with an increase in the thickness of the neve layer from the coast inland.Taken from the S2 Trail Marking Trip section of the document:Although the main purpose of this trip was to remark the S2 trail with drums, and depot fuel for the two spring traverse, one and a half weeks were spent at S2 on glaciological and geophysical work.The geophysical work was wholly devoted to the study of vertical seismic primary waves in ice. Firstly a velocity profile was shot with the intention of determining the average vertical velocity to bedrock. The results of the profile were poor due to the poor quality of reflections obtained. Secondly an uphole shoot was carried out. A 170 ft deep hole drilled in 1964 was used. One point charges were fired in the hole at 20 ft intervals commencing at 170 ft and working upwards. The time taken for the shock wave to travel up to the surface was recorded by geophones at the top of the hole. The results of this method have allowed an accurate velocity-depth profile to be drawn up for the top 170 ft of the ice cap at S2. On comparing these vertical velocities with the corresponding horizontal velocities deduced from refraction shooting it was discerned that ice is fairly isotropic as regards compaction etc.Take from the Spring Traverse section of the document:The spring traverse took the firm of a grid, the starting point being at S2. The main legs of the grid run exactly north-south and are spaced at 10 mile intervals.Seismic reflection stations were installed every ten miles around the grid except at D20, D40, D60, and D80 where reflection probes have been shot in previous years. Instead, refraction shooting was done at these points to gain more knowledge of seismic ice velocities.Gravity readings were taken every mile both on the main legs and on the sidelegs. Elevation readings, using precision microbarometers, were taken every fifth of a mile and simultaneous elevation readings were taken every mile.Navigation was by dead reckoning. The north-south line was turned off from an east-west azimuth, installed at S2 in 1964, using a theodolite. The line was kept by backsighting on stakes planted every fifth of a mile. Distances were measured using a modified Weasel speedometer fitted in the Snowtrac, the lead vehicle. This navigational technique was very successful, the fact that the traverse finished only one mile east of the starting point stake at D00 speaks for itself.As progress was better than expected, 70 miles more than was originally expected were traversed. This extra work provides a good coverage of the inside of the triangle.