This PIRE project brings together an international team of U.S., Bangladeshi, Indian, German, and Italian scientists to further our understanding of the dynamics of the world's largest delta, the Ganges-Brahmaputra-Meghna Delta (GBMD). This delta, named for the three large rivers that flow into it from the Himalayan and Burmese Ranges, encompasses most of Bangladesh. In addition to its size, this delta is notable because it is at the active juncture of three tectonic plates, and receives over one gigaton of sediment annually from the three large rivers. About 1/3 of this sediment remains in the delta because it is rapidly sinking. This combination preserves a tremendous stratigraphic archive of erosional processes in the Himalaya, the river-based processes that are building the GBMD, the tectonics of the active plate boundaries it overlies, and the interactions among these processes. This record is largely unexplored and little is known about the fundamental interactions between sedimentation and tectonics at this scale. This PIRE team will use a broad suite of disciplines and techniques to collectively study the sedimentary and hydrological processes, tectonics, structural geology, and seismology essential to unravelling GBMD dynamics.
The PIRE team will first create a record of the stratigraphic architecture of the delta using a mixture of advanced technical and local manual methods. Core areas of the project include: 1) defining the tectonic plate boundaries that are buried by sedimentation; 2) identifying potential sources of future earthquakes; 3) investigating the causes of the subsidence rates due to longer term effects (e.g., sediment loading, tectonics, and compaction) vs. shorter term effects (e.g., earthquakes and human interventions); 4) investigating rapid channel switches of the Ganges and Brahmaputra rivers; and 5) assembling a comprehensive, integrated record of delta dynamics by coupling tectonics and hydrological processes, and by linking long-term steady processes with abrupt, short-term events.
Bangladesh is a developing country that is the size of Iowa, but with a 50-fold greater population of almost 160 million people. This impoverished nation is extremely vulnerable to natural hazards related to the dynamism of the delta system. Such hazards include widespread seasonal flooding, river erosion and channel redirections, permanent land loss from sea level rise, naturally-occurring arsenic in groundwater, recurrent cyclones and monsoons, landslides, and huge earthquakes. Because the infrequent geologic events are poorly understood, there is little long-term planning to address the timescales at which the dynamic GBMD landscape is changing, leaving a growing population at risk. Reliable knowledge of geologic processes is therefore a prerequisite for effective infrastructure design, risk-reduction and resource optimization in Bangladesh.
The PIRE project provides a compelling international education opportunity for all participants by collaboratively engaging them in research on an important fundamental problem, the results of which could reduce the impact of future delta-related hazards. It will train the next generation of U.S. earth and environmental scientists to work globally via international fieldwork, laboratory experiments and analysis, and modelling. Graduate students and undergraduates from PIRE institutions will be able to enrol in interdisciplinary field courses and schools in Bangladesh; additional research trips and field schools will also be open to students from institutions not directly involved in the PIRE research efforts. The project will also broaden participation across PIRE institutions and strengthen the geosciences dimensions of an interdisciplinary course on water issues in Bangladesh taught at the University of Minnesota.
The PIRE project will allow the U.S. institutions to build their capacity for international engagement. It will strengthen and link longstanding ongoing research involvement in Bangladesh on several campuses. It will couple the U.S. institutions in an international network of delta experts in Europe and South Asia. Members of the project will also take advantage of the unique “Experimental Earthscape” and computational facilities at the National Center for Earth-surface Dynamics (NCED), an NSF-funded Science and Technology Center at the University of Minnesota. Linkage to NCED, which supports many researchers studying the Mississippi River delta, means this PIRE has the potential to have a large national impact by providing fundamental new insights into the behavior of delta systems. This award will also help build Bangladeshi research capacity and infrastructure via the collaboration with the Delta Study Centre (DSC) and Dhaka University Earth Obseratory (DUEO) at Dhaka University (DU). The project should help position DSC and DUEO as centers of excellence on deltaic sedimentary and tectonic processes and establish it as a focal point for GMBD research with strong faculty, archived sedimentary data, and oversight of critical seismic and GPS networks.
Topographic map of the Ganges‐Brahmaputra-Meghna Delta (GBMD) region. The GBMD is bounded by the Indian Shield, Shillong Plateau, Burma Arc and the continental margin. The borders of Bangladesh are indicated by the red line. Thrust boundaries are marked by black lines with ticks on the upper plate, dashed where uncertain. The Hinge Zone, marking the transition from thick continental crust to thinned continental or ocean crust, is noted by the dashed gray line. M, Meghna River; O.B., Old Brahmaputra River. (Steckler et al., 2008)
Dhaka, the capital city of Bangladesh. Bangladesh is a developing country that is the size of Iowa, but with a 50-fold greater population of almost 160 million people. This impoverished nation is extremely vulnerable to natural hazards related to the dynamism of the delta system. Photo by Chris Small, 2005.
Photo and line drawing of tubewell drilling. Method uses percussion drilling by lifting and dropping the drill tube with circulation created with a mud pit supply drilling fluid that is expelled out the top of the drill pipe during the percussion, controlled by the human flapper valve at the top of the drill pipe. Wash samples are expelled out of the top of the drill pipe either as slurry (sand) or solid plugs (clay). Intact split spoon samples are also regularly taken. Even subtle lithological changes are immediately detected by drillers.
Map showing the broad paleochannels that dissected Bangladesh during the last glacial lowstand and fed the Swatch of No Ground Canyon. We will drill dense transects across these valleys (red) to capture the complete Holocene pathways of the rivers. Additional transects will cross the Dauki Fault. Sparser transects are dashed. Blue circles represent permanent GPS and seismometers. Light blue circles, continuous GPS to be continued in this project. Open circles, portable seismic array deployments in the Sylhet (S) and Tangail (T). The latter has been the size of numerous earthquakes over the last 12 months. Tectonic boundaries in black. Mad., Madhupur Tract. (Modified from Goodbred et al., 2000; Umistu, 1993)