Unusual seismo-glacial landforms in Lapland

Fig. 1. Distribution of seismically induced landforms especially near the village of Kallo.
 (basic map © National Land Survey)
 
As the Finnish elevation model has evolved, new landforms have been revealed.
Now this happened in the Kittilä region (Fig.1). There are occurences also outside the map. I have outlined the location of mainly three main types of special landforms. I have not seen quite the same elsewhere, but of course if you know what to look for, the searcher will find it easier. Further northeast towards Saariselkä, there is a somewhat similar network in places, but polygonal and subtle, which may also be patterned during the periglacial phase without seismic influence. Northeast of Kuosku (Savukoski) there are also some similar but minor occurences as in Kittilä.

Certain deformations appear to be formed, both for relatively large formations of moraine or fluvioglacial material and also for smoother areas. The main "new landform types" are 1) grid-like surfaces, 2) fields of small spherical mounds and 3) other related landforms including minor landslides, mass flow formations, liquefaction bowls, and perhaps till or sand blows, too (Fig.2.). Without further examination and terrain research, interpretation of landforms is so far tentative.

The "1) ditches and 2) "balls" form a relative topography of up to about 2 meters height, but other related landforms in the area may be considerably bigger. The distance between the grid ditches varies and is e.g. 10-50 m. Round humps and ridges often have a width of about 15 m. Individual pattern areas are often 2-20 ha in size, but can form concentrations of more than a square kilometer. There is a lot of gradual variation in form within the patterns inside the categories and from category to another reflecting the local progress and intensity of the seismically induced process.

Fig.2. Seismo-glacial landform surfaces. 1) Grid-like 2) sphere-like. One more landform type in the picture could be seismically induced landslide or mass flow edge of the formerly mentioned categories. These processes can produce also bigger crescent and other odd forms among others.
(Hillshaded map © National Land Survey)

These are probably earthquake-induced and liquefaction-induced deformed till and sand formations (Obermaier 2009). Some of those are described also before from paleoseismically active zones in Lapland (e.g. Sutinen et al. 2018, Sutinen et al. 2019a, b): Pulju moraines, liquefaction bowls, other liquefaction-induced deformations and mass flow formations. But except for Pulju moraine and  liquefaction bowls those cases do not show distinct structures and strange shapes as can be seen directly from the elevation model in Kittilä.

Seismo-glacial landforms in the area have apparently been shaped and are now visible horizontally as described vertically in the textbooks of soft-sediment deformation structures (Obermaier 2009, Fig.7.3). Of course, the development of the peculiar and diverse surface morphology in the area has been widely influenced by many seismic and other processes. There are also Pulju moraines, other seismically induced deformations, mass flow deposits, landslides, liquefaction bowls and so on, There are intensive postglacial or late glacial faults, which is the basic explanation or connection that these landform surfaces occur in the area. The area has also been intermittently an ice divide zone and therefore is not patterned very much by sharp active ice and other deglacial landforms, but the smooth surface gives a good background for seismically induced formations or numerous meltwater channels and deposits and bedrock faults to gain visibility.
 
Apparently, where ditches or grids are now visible, the earthquake has shaken a firmer surface layer over the liquefaction layer to form tiles or ditches. As the deformation progressed, the earth slabs were moving, shrinking, and in some places forming spheres, which may be partly sand blows. Excess material moved to the edges of the earlier hummock or a little higher plateau, forming edges and slopes that were thicker inward than outward.

Another alternative to the emergence of these geometric shapes could be periglacial processes without any seismic effect. In that case, it would be a patterned ground phenomenon. And there could be hypotheses for genesis based more on meltwater activities.


References

Obermeier, S.F., 2009. Using liquefaction-induced and other softsediment features for
paleoseismic analysis. In: McCalpin, J.P. (Ed.), Paleoseismology. International
Geophysics Series. 95. Elsevier, Amsterdam, pp. 497–564.

Sutinen, R., Hyvönen, E., Middleton, M., & Airo, M. 2018. Earthquake-induced deformations on ice-stream landforms in Kuusamo, eastern Finnish Lapland.Global and Planetary Change, Volume 160, January 2018, Pages 46-60

Sutinen, R., Andreani, L., & Middleton, M. 2019. Post-Younger Dryas fault instability and deformations on ice lineations in Finnish Lapland. Geomorphology. Volume 326, 1 February 2019, Pages 202-212.

Sutinen, R., Hyvönen, E., Liwata-Kenttälä, P., Middleton, M., Ojala, A.E., Ruskeeniemi, T., Sutinen, A., & Mattila, J. 2019. Electrical-sedimentary anisotropy of landforms adjacent to postglacial faults in Lapland. Geomorphology, Volume 326, Pages 213-224.

Murtoos, if ideal form: diamond-shaped or triangular morainic landforms

Figure 1. Murtoos around Salmineva bog in Central Ostrobothnia in Toholampi Municipality. There are also arrowhead shaped, and other form variants. Bigger moraines are ribbed type moraines. (Hillshaded map © National Land Survey, Map sheet Q4114H)


Who would raise the cat's tail if not the cat himself. But in defense I can say that I can partially echo what others say, and many thanks to them.

"Murtoos are typically 30–200 m in length and 30–200 m in width with a relief of commonly <5 m. Murtoos have straight and steep edges, a triangular tip oriented parallel to ice-flow direction, and an asymmetric longitudinal profile with a shorter, but steeper down-ice slope." "Murtoos are composed primarily of loose diamicton with some sorted beds."

"The first modern mention of murtoos (though not yet named) appeared in an
article written by Seppälä. The author identified the triangular landforms
from LiDAR images, and referred to them as ”fan-like hollows of plucked
or glaciotectonic rafts” with a general edge height of 1-3 meters (Seppälä,
2016, p. 4), in contrast to later publications originating from both Finland
and Sweden, where murtoos are considered to be positive mounds."

Ok, that description concerned one place. But I also described it this way: "Tightly spaced fan-like fragment lines produce diamond patterned moraine surfaces." So as I have used the term glaciotectonic or deformational, in this context, it is much the same as "Murtoo-like" or "concerning Murtoos". In my classification (see below) Murtoos are partly covered by both category 3): fan-like and transverse edges of plucked depressions and category 5): deformational or glaciotectonic mound or ridge. All Murtoo fields do not show clear fan-like faults, but fault or edge system can be more complicated, skewed or obscure.

Erosion and deposition in this case are perhaps like the choice of whether the glass is half empty or full. For the time being, I prefer the negative option in most cases until proven otherwise. I think the simplest explanation for triangles and corresponding forms are the motion-conjugated symmetric oblique edges ( that were created by glaciotectonic fracturing of the substrate as the glacier moved forward. The meltwater weighted formation option does not explain triangles "at all".

So I have dealt as the first current (2015, 2016a,b) researcher triangular morainic landforms, Murtoos, but in a broader context and with a different genetic interpretation (deformation or glaciotectonics): the so-called subglacial glaciotectonic hypothesis (SGH). According to SGH, these would be mainly erosional forms, ie in the case of triangular ridges, they would be the result of the erosion of ridge spacings directly as a result of glacial/glaciotectonic activity. It may have preceded and followed also the subglacial meltwater processes, but in essence, it would have been, in my early interpretation, subglacial block-erosion.

Glaciotectonic activity may have been not only plucking but also ductile deformation, less deforming or reforming, and even possible squeezing or massflow. These are alternative glaciotectonics related processes for the subglacial meltwater erosion and deposition. Thus, I have formed a short description of the classification of the related mostly subglacial glaciotectonic or deformational formations: Five types of mostly erosional glaciotectonic landforms were recognized: (1) plucked lee side, (2) hill-hole pair, (3) fan-like and transverse edges of plucked depressions, (4) sporadic plucked hollows, and (5) deformational or glaciotectonic mound or ridge. The Murtoo topography is essentially same as the class 3: fan-like and transverse edges of plucked depressions or diamond-shaped morainic topography or fan-like hollows; and as the class 5): deformational or glaciotectonic mound or ridge.

As simple speculation, possible meltwater related processes behind these landforms could be subglacial sheet-like outbursts, which could explain wide erosional spacings between hummocks and also sorted layers of hummocks, but not so obviously diagonal edges or triangles. The source of meltwater flows could also be moulins, which could explain often punctuate proximal endings of the erosional fans. But moulins are maybe not so good explanation for close adjacent shapes? These meltwaters could occasionally freeze onto the substrate and glacier and thus cause glaciotectonics. If the moulins reached a depth of up to one hundred meters, it positioned the origin fairly close to the front of the glacier. The differentiation of glacial landscapes from low valleys with rough (plucking?) moraine topography and smooth drumlinized (abrasion) higher areas could also be related to transverse drainage of meltwater on, in or under the glacier? But the overall rough image of these landscapes speaks for glaciotectonics and secondly for all kinds of erosion. Fragmentary and triangular shapes are most easily interpreted as directly attributable to the characteristics and motion of the glacier, even if, for example, there are also partial meltwater flows at the beginning and end of the overall process. The moving ice could produce pairs of symmetrical displacements to the substrate with an angular opening in the direction of motion, which explains the fracture lines that produce the triangles. Apparently, both the glacier directly and perhaps in some cases, meltwater then caused erosion in the areas between the positive shapes, and with the possible glacial deposition inside the triangle, a typical morphology formed. Also, it is good to remember that especially along existing watercourses some fragmented looking topography can partly or wholly be the result of quite late postglacial fluvial erosion.