Tuesday, August 8, 2017

Axel Heiberg Adventures Part II

                Hello, hello, and welcome to Part II of our Axel Heiberg field adventures! As mentioned last post, we moved campsites about half-way through the trip. The plan was to move from Lost Hammer Spring to South Fjord Diapir. South Fjord is the largest salt dome on the island at a monstrous 5 km diameter! We were to make the move in three trips by helicopter. Oz and I would go first with our personal tents and some other essential gear, the helicopter would return and pick up a net load (literally, in a hanging net) of other gear including the fat bikes, and then on the third trip would bring Mike and Mark with the communal tent and the remaining gear. So Oz and I took off, needing to scout for a place to land that would be safe, accessible, and geologically interesting. But in a 5 km-wide mountain of continually rising and crumbling salt, what could not be interesting?

Until we got there.


That’s, um.  Hmm.

Well, at least we can confirm South Fjord Diapir has rough surfaces.
There is too much snow! We can’t possibly land here! Oz is shocked – it is mid-July and South Fjord Diapir is a winter-wonderland. He said that he visited this site in late June some-years ago, and there was nowhere near this much snow. This has some interesting implications for remote sensing work. Snow and ice can heavily influence radar response – what if South Fjord dome was blanketed in snow when our radar images were taken? I resolve to check Landsat images taken around the dates our radar images have been taken. I have done this since returning – it does look like one of our six images might be affected – perhaps I should mask out the ice and snow and redo the radar zonal statistics extraction!

What do we do? We flew around the dome for a bit, taking pictures while deciding where our backup camp will be. Remember that helicopter time is a valuable resource, so we need to decide quickly. Oz asks if there is a diapir near the end of Strand Fjord. I recall that there is, but I don’t know the distance to it. As we begin to fly over there, I pull out the field laptop that I had in my backpack. I’ll admit, I felt pretty cool flying in a helicopter while measuring distances in ArcGIS to make quick decisions where to land. I determine that Strand Diapir is approximately 6 km from the shoreline, and we deem this close enough to hike to.  We’re off to land in Strand Fjord!

And oh, what a beautiful campsite it was!

Icebergs in the Fjord, a low fog is rolling through. The dark rock unit is an folded igneous sill.
The brown rock is gullied the surface has undergone solifluction.
Strand Fjord, near our campsite.
The sandy banks have compositional layering.
I honestly think this is the most wonderful place I’ve ever camped. We had glaciers and ice bergs and beautiful sharp mountains with intense solifluction. It was beautiful. I did some soil sampling between our camp and the Fjord on one of our off days. 
Again, we saw patches of precipitated salts. Interestingly, these salts tended to be concentrated along the rims of wet/dry sand boundaries. The whole fjord area shows up in the TIR images as having VERY STRONG gypsum/anhydrite signatures, all deriving from the nearby Strand Diapir. Mike, Mark and I went on a hike to visit the northern half of the diapir exposure one day. 

The inland-area of the Fjord appears to be a glacially carved U-shaped valley, so Strand Diapir is split into two main outcrops across the valley. The salts in Strand Diapir are also interacting with some volcanic intrusions, causing some beautiful iron staining.

Behind me is the glacier that carved the U-shaped valley and provides the meltwater for the river.

The brilliant colours are from oxidation reactions between igneous rocks and the diapir.
The igneous rocks provide the metals, the anhydrite provides sulphur.
A reoccurring theme, the outcrops show some exposures of intact rock salt, but the majority of the surface has weathered into the highly vuggy gypsum crust that is characteristic of the Axel Heiberg Island anhydrite diapirs. Part way up the valley wall, the anhydrite is interbedded with what I think is limestone. I haven’t exampled the sample yet, but the dark colour and texture looks like a carbonate and past literature states that limestone is commonly interbedded with the Otto Fjord Formation salts. On a regional scale, the diapir material is stratigraphically overlying the orange stained unit, which I think is a volcanic sill, and has since undergone synclinal folding.

Flying in a helicopter never gets old
Something that I really appreciated this trip was being able to finally investigate the mystery of the radar-dark bright region, mapped as Isachsen Formation (quartz sandstone with some igneous intrusions). As a weather front was rolling in, our helicopter pilot asked if we wanted to make any last quick visits. I gave him the coordinates at the centre of the feature – the peak of a broad mountain range. He looked westward, and observed that that was where the storm was the thickest, and he wouldn’t be able to land there. Nonetheless, we headed that way along the coast, wary of the thick clouds in the distance. The very peaks were shrouded in clouds, but he asked if seeing the sides were enough. Elated to be there, I said yes, and to my delight we made a full perimeter tour around the feature before heading back to the safety of our campsite. Many photos were taken, and the verdict is that these slopes are COVERED in cobble-sized talus that would effectively scatter RADARSAT-2’s 5.6 cm radar beams. Since these are also high elevation peaks, snow and ice is admittedly also a possibility. I’m going to check the Landsat images soon to investigate. Sadly because we couldn’t land I wasn’t able to sample, or get good scaled photos. -sobs-
In addition to the fist-sized rocks everywhere,
take a moment to appreciate that sweet folding.
Travertine terraces from perennial spring from Colour Peak
Finally, one of the highlights of the trip was scaling the 550 m Colour Peak. Colour Peak has been part of the epitome for my thesis, showing that salt diapirs are radar-rough, whereas the materials that erode off of them and reprecipitate elsewhere are radar-smooth. Mark and Mike spent the day sampling the calcite-rich perennial springs effusing from the base of the mountain. The springs are building terraces of black travertine – the type of calcite that precipitates from cold water springs. 1-3 mm cubic halite crystals lined the edges of the streams. Mike founds some really cool crystals in a small cave – the sample he gave me is decorating my coffee table as I write this. The smell of H2S was pungent, and I found myself craving egg salad whilst down there. 
Oz and I, however, journeyed up to climb the massive diapir.  The best exposures of salt textures were at the top, with the flanks being either covered in soil, talus, or completely weathered and crusty outcrop.  The ascent was tough.  The diapir is steep sided covered in poorly sorted colluvium. The skree contains sand to boulder-sized rocks. We also found some palm-sized fragments of clear selenite crystals amongst the soil patches. I think the anhydrite colluvium and gypsum-rich soil is enough to product the spectral signature seen in the ASTER TIR image downslope of Colour Peak without us needed to appeal to the perennial spring. Because much of the slope material was unconsolidated, our feet were prone to slipping down as we moved upwards. I’m very fortunate that Dr. Osinski is an experienced climber, and I was able to follow where his footsteps packed down the debris.  Frequently we would take a step on what seemed to be solid ground, only to have our foot punch through the weathered gypsum crust into a 20 cm deep vug.  
Rough, steep, the return of slightly karst-y topography.

Close to the summit are outcrops of solid anhydrite or gypsum. Unlike at Wolf Diapir, where the solid salt was powdery and friable, here the salt is crystalline.  Erosional processes are carving the solid salt into points like the rillenkarren seen on halite diapirs and in karstic carbonates. The rillenkarren are smooth at the mm scale, but undulate at the cm scale and would appear rough at C and L-Band SAR. 
Rippled rillenkarren textures on crystalline anhydrite sample.

The sharp, solid salt looks beautiful up close.  Of course, nothing compares to the stunning, beautiful view from the summit!


An excellent view across Expedition Fjord,
            and the travertine perennial spring down below


The rocks up here are mostly blocky, partially weathered, and the ground is covered in colluvium. Once again we are able to confirm that salt diapirs are rough on the ground, not just in radar.

Very blocky, rough, and sadly too unstable and dangerous to venture farther.
You can see where Colour Diapir ends, and the adjacent mountain begins
based on surface texture alone. 
  Any discussion of Colour Peak would be incomplete without explaining how it got its name. The colluvium also includes rubble and gravel of angular igneous lithologies, including what is ostensibly dacite and diorite. Some of the volcanic material is oxidizing to form gossans. The gossans are dazzling zones of vivid orange, yellow, and brown alteration. These are found in close association with diapirs on Axel Heiberg Island, including North Agate Fjord and Junction Diapir where basaltic intrusions from the Isachsen Formation are altering to form copper and iron sulphides and secondary copper sulphates (Williamson 2011). The calcium sulphates in the diapir provide the sulphur for these alterations to occur. Remember, we saw this same alteration at Strand Diapir!  We collected some samples of yellow rhombohedral crystals have been taken to the lab to for analysis

The journey home was bittersweet. I’m going to miss this place.

And such concludes my 2017 Axel Heiberg adventure.
Elise xx

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