The northern area of Cao Bang Geopark, mainly of Ha Quang district and part of Hoa An and Tra Linh districts, is of Luc Khu massif, another famous karst massif of Northeast Vietnam. The massif’s height descends from 1000m in the northwest to 700m in the southeast, gradually leaning toward a very large karst area east of Ma Phuc pass – the so-called Quang Hoa karst plateau. It is also a karst plateau but compared to the Dong Mu karst plateau, the karst evolution here is in the older phase.
The karst evolution intensifies from northwest to southeast. In the northwest, the main karst landforms are ranges, peak-cluster depressions with cones that surround closed valleys where the vertical erosion process still prevails.
Rain water quickly disappears to underground, so surface water is rather scarce while groundwater is plentiful. To the southeast is the mature and old karst landforms with karst towers, pyramids and cones which have been or nearly separated, surrounding wide valleys; their bottom is quite flat and close to the local erosion level. At this point, the Tra
Linh River connects these valleys to form the Thang Hen “turlough” lake system – a unique scenic spot of Cao Bang Geopark. A number of karst-tectonic heritage features can be observed in this area, in addition to the Thang Hen Lake System already introduced in Section 3.1.3, as follows: – Karst landforms showing different stages of karst evolution in Keo Yen commune, Xuan Hoa town, Ha Quang district (X=610200; Y=2533000; z=302m asl);
– The strongly fault-dissected and eroded southern part of Luc Khu karst plateau (Quang Trung, Nguyen Hue communes);
– Young karst landform around Pac Bo cave – a part of the weakly dissected Luc Khu plateau;
– Old karst landform on 700- 1000m planation surface in the south of Pac Bo, in Coc Chu area, Phu Ngoc commune;
– Geological-geomorphological-paleontological heritage cluster in Ha Thon commune, Ha Quang district (X=620000; Y=2523000; Z=677m asl);
– The NW-SE fault slip surface in Lung Dam village, Van Dinh commune (X=612034; Y =2534235; z=721m asl);
– Hanging valley with karst cones on its surface in Soc Giang commune (X=614079; Y=2534763; z=829m asl);
– Expressions of neo-tectonic activity in Dan Chu commune, Hoa An district (coordinates X=609184; Y=2522350; Z=206m asl);
– Traces of river terrace and active caves in Hoang Tung commune, Hoa An district (coordinates X=619422; Y=2509842; Z=195m asl);
Karst landscapes showing the early, young and mature stages. View from Keo Yen commune