What would an impact do to the landscape? To prepare for the expedition and to further understand the landscape that we would encounter we obtained Landsat 7 imagery and Defense Mapping Agency (DMA) maps which contain topographic information and a useful overlay kilometer grid.

Gunther uses these tools to address a possible working hypothesis for the modification of the landscape and its reconstruction.
The ICE2002 began with images from satellites hundreds of kilometers above the ground. And indeed this image is the only solid evidence about the suspected structure that we have available before the expedition. We also obtained a topographic map about the area from defense mapping agency but as you can see there is no clear evidence of the suspected structure, even though we know it is there (see LANDSAT image spectral band 40).
The Landsat 7 satellite image set contained multiple spectral band records. Most of the information of interest to us is contained in two different spectral bands called here bands 40 and 50. Different spectral bands contain different type of information and more detailed information about them will follow in future discussion. The best example of this relationship is illustrated by the bands 40 and 50 in Fig 2. The grassland according to topographic map is represented by dark area for band 40 but by relatively light area for band 50. However, the circular structure outline, other than the grassland, is in both cases represented by relatively darker regions.
Since we will not "see" all of this detail once we are on the ground we want to design the best possible approach when exploring. Satellite images contain much more information about slight changes in elevation, based on the appearance of multiple drainage patterns ,than the topographic map in Fig 1A. However, the topographic map contains very clear indications about the flow of the major streams in the area. Most streams run from southwest to northeast. If we now closely examine the small intermittent stream cutting across the suspected structure on satellite images we can see that the structure appears to dictate the exact path along which the small stream can flow. And this pattern can provide us with more detailed information about the small changes in elevation that are caused by the suspected structure.
Based on the satellite information about the stream directions we can assume that before the origin of the circular structure the general stream flow pattern was also in northeast direction. We postulate that the placement of the structure perturbed the preexisting stream flow pattern and caused the intermittent stream drainage to follow a new topography caused by the origin of the suspected structure. As we can see, one stream (stream A) originates 2-3 kilometers southwest of the structure (structure is about 8 km in diameter) as a junction of multiple smaller streams and approaches the circular rim almost directly at the southern end . Stream A follows the rim eastward until it meets with the junction of other streams. One stream (stream B) flows northeast and one stream (stream C) flows in almost an opposing southwest direction. If we follow the stream C upstream we can detect that in the satellite images (especially band 50 in Fig 2) there is an indication of preexisting drainage joining this stream C with another one, stream D, in northeast direction. Stream D, however, flows in the northeast direction based on the topographic map. This observation suggests that the stream A was once connected via stream C with the stream D and flowed along the circular rim that was left in eastern parts in order to continue to flow in the northeast direction.

However, today stream A turns sharply northwest upon joining stream B and C. About 1 km before this sharp turn there is a relict drainage of another stream going from the rim directly to the center of the circular structure. Similar relic drainage pattern towards the circular center is also evident about one km northeast from this sharp turn of stream A. In between these relict drainages there is a multiple drainage pattern suggesting that more of the smaller scale streams once flowed directly to the center of the circular structure. These preexisting drainages directed toward the center of the circular structure clearly indicate a topographic relief that was caused,, most likely by a depression of the center of the circular structure. Streams flowing along the slope of this depression were most likely braided streams, streams of relatively fast sediment transport, and distinct from the meandering stream patterns, which are characteristic for this low-relief area. Fast sediment transport would prefer deposition of coarser grained sediment along these drainages. There is an indication that similar preexisting drainages may have existed also in the western part of the circular interior, where spectral bands 40 and 50 indicate linear features, which may be the evidence of relatively fast flowing streams directed towards the center of the circular depression.

In summary the evidence from the satellite images suggests the following character of the depression (<<LEFT):

The circular depression has an uplifted rim, at least in the southeastern part of the rim. This is evidenced by the stream that was directed along the edge of the rim. The water level that once existed along the rim must have been quite substantial in order to reverse the flow direction in the stream C and connect with the northeast drainage pattern of the stream D (Fig B). Thus following the formation of the circular structure whose rim must have been elevated the water coming down along the stream A most likely pooled outside the rim in the southeastern section. The raised water level starts to overflow the rim and causes a quick draining of the accumulated water along the multiple streambeds towards the center of the depression (Fig C). The water overflow possibly causes formation of the lake in the middle of the circular depression. The water then exits in the northeastern part of the circular rim and drains the lake (Fig D).

Landscape reconstruction of the suspected area based on satellite images. A is a land before the circular structure origin. B is the paleo-indication of stream-regime disruption immediately after the origin of the circular structure. C is the paleo-indication of the flooding of the depression. D is the current drainage system.

The model just presented is just one possible scenario that may explain the satellite evidence. With this model in hand, how would you go about testing the hypotheses contained within this model? By the way if this model is true, it rules out the origin of the depression by some kind of ground collapse because of the existence of the elevated rim. This is inconsistent with just a simple collapse structure.

You have been given the tools to create a model just as Gunther has done. All the necessary information can be found at the web site. Your model may be the correct one! TRY IT!

© 2002 Blue Ice International