Access and “Things To Be Aware Of”
Drive towards Middlemarch along SH87 until you reach Sutton [9km before Middlemarch], turn left here onto Kidds Road. A km or so along from here is the DoC carpark and access to the track to the salt lake.
To complete this Earthcache there is no need to walk on to or in to the Lake [bed] itself.
Background
The Sutton Salt Lake is the only saline lake in New Zealand, and has formed in a windy cool-temperate maritime climate. Consequently, the lake is distinctly different from most of the world's saline lakes that form in arid continental settings. Sutton Salt Lake forms annually in a shallow (5 m) bedrock-floored <2 hectare depression c. 50 km from the nearest coast.
The site receives c. 500 mm/year rainfall compared to coastal rainfall near 1000 mm/year because of a minor rainshadow effect of coastal hills. Surface evaporation rate is high (c. 700 mm/year) because of frequent strong winds. Sediments on the lake floor are derived by rain and wind erosion of the surrounding quartzofeldspathic schist bedrock, with a contribution from organic sources, particularly ostracods, and evaporative halite. The sediments have a higher proportion of phyllosilicates (muscovite, kaolinite, and chlorite) than the source rocks because of differential transport of these minerals into the lake depression.
Lake water is entirely derived from rain, rather than groundwater, and the lake waters have had minimal chemical interaction with bedrock. Lake water pH is near 9 and pH of pore waters in drying lake sediments is near 8, compared to pH near 7 for regional surface and ground waters. When full, the lake has salinity about one quarter to one third of that of seawater, and ion ratios are similar to sea water. The lake salinity is derived from marine aerosols in rainwater concentrated by about 20 000 evaporation and refilling cycles in the lake depression.
Logging Requirements
Information can be calculated at the site (or later).
0. Preface any email with Sutton Salt Lake in the subject line and title and clearly note the question number and answer. Do not wait for a confirmation email to log but be prepared to be asked for additional information if your answers are slim.
1. First the easy bit – From the indicated coordinates upload a picture of the Salt Lake with the Rock and Pillar Range in the background. Include your GPSr in the foreground. As pictures are added it should show the differing lake levels during the year
Now go for a walk around the Lake and use your GPSr to record the following:
2. The length of the perimeter of the Lake [in m]
3. The area of the Lake [in hectares]
Email me the two answers, I will be generous with the margin of error...!
DO NOT WALK IN OR ON THE LAKE.Use the footpath where appropriate and then continue around the grass/tussock to your starting point.
[You may need to find out if your GPSr does area calculations for you. If not then you'll have to use the track information in conjunction with some other software to work this out. I set my GPSr to record the track every 10m]
Thanks to U.N.C.L.E. for pointing out that only some GPSrs can calculate area themselves.
If you have mapsource [Garmin products] then you can do the following:
- At the lake reset your track and walk around the lake and then save the track.
- At home upload the track into Mapsource
- You will want to show the track length and area by right clicking on the column headings
I have included a screenshot of a track taken when I cycled around the Swampy MTB circuit showing in Mapsource on the cache page.
Acknowledgements and Sources
The text was published in the following paper: D.Craw & S. Beckett, 2004. Water and sediment chemistry of Sutton Salt Lake, east Otago, New Zealand. New Zealand Journal of Marine and Freshwater Research, 2004, Vol. 38: 315-328
With permission this EarthCache has been included into Stegan's EarthCache Masters Programme.
2010 Stegan’s EarthCache Masters Programme
Since it is not very feasible for many NZers to easily get more than two states for the earthcache.org masters programme and therefore not get past Bronze I’m running my own one on a number of Earthcaches that I plan to release this year (all things being equal) with the following points system:
5 points: First to find
3 points: 2nd to find
1 point: Logging a find
1-5 points: Special bonus questions.
At the end of 2010, I’ll issue certificates for 1st, 2nd and 3rd and the first place getter will be awarded a geocoin. If I feel richer and/or it looks like this is popular I’ll upgrade the prizes.
Updated information and Leaderboard at: Stegan’s Earthcache Programme