Age and backfill/overfill stratigraphy of two tufa dams, Tigray Highlands, Ethiopia: Evidence for Late Pleistocene and Holocene wet conditions

Geomorphological mapping of parts of the Mekele outlier reveals the presence of numerous river tufa dams, spring tufas and old landslides, indicating high groundwater levels and karstic activity in the area during former times. U/Th dating of river tufa dams indicates that wet conditions prevailed in the highlands as early as 15,000 BP. This is 4 to 5000 years before the first signs of post-last glacial maximum (LGM) humid conditions deduced from former lake extensions in the Ethiopian and Kenyan rift. Tufa build-up and the corresponding wet conditions in the highlands gradually came to an end from 5000 BP onwards. In the study area, environmental deterioration started around 3000 BP and is explained as a result of forest recession. Evidence is presented, showing that forest retreat and land degradation in the area is not climate-driven but the result of human activities.