CORE SCANS OF LAKE TOWUTI
by James Russell

Lake Towuti began to form about one million years ago, when movements of Asia, Australia, and the Philippines reated fractures in the Earth’s crust. Movement long these fractures allowed the region of Towuti to sink, creating the 200-meter-deep depression the lake occupies today. During its initial stages of formation, lake Towuti was much smaller than today, and oftentimes existed not as a lake but a swamp, as depicted in the formation of peat, the sediment composed by remains of grasses, trees, and other plants. This contrasts dramatically with the green, banded clay that form in the deep lake today, where the sediment is composed of fine mineral material washed in from the soils and the remains of algae and other micro-organisms that live in the lake. Indonesia has been an extremely active region geologically throughout the past million years, with frequent volcanic eruptions that spew ash into the atmosphere. Much of this ash falls onto Lake Towuti and is buried in its sediments. Although these eruptions are often very destructive, they release nutrients into the water, stimulating biological productivity by diatoms and other algae. Reproduced here are four core scans we’ve produced at our labs since the expedition in 2015. In all, we drilled ten boreholes, which are anywhere from about 40 to 180 meters long, and cores from each hole are sectioned into 0.1-to-1.5-meter-long parts. This equates to over 1,200 core sections, each of which has a separate image, so this is just a very small subset of the images we have available. When viewed together, the core scans connote large changes over immense time-scales. Sediments vary from dark to light, red to green, and each of these colors is code for large environmental perturbations. In particular, large shifts between red sediments and green sediments record large changes in the lake level, driven by wet-dry cycles in regional climate that appear linked to the Earth’s ice-age cycles. These lake-level shifts cause large changes within the lake ecosystem and surrounding landscape. Even within each individual core section, there can also be visually interesting features, including aminations that record short-term rainfall and drought cycles. Finally, if we move beyond the macro-scale scanned images, we have microscopic images of fossil pollen, fossil diatoms, minerals, and ther materials from these cores, which tell us the composition of the sediments and can also be quite visually arresting.