PRACTICAL REMEDIAL MEASURES TO DEAL WITH RED BOLE DURING LOCATION OF FOUNDATIONS FOR STRUCTURES

V T LONDHE 28–04–2015

The Deccan Traps is a large igneous province located in west-central India and is one of the largest volcanic features on Earth. It consists of multiple layers of solidified flood basalt that together are more than 2,000 m thick and cover an area of 500,000 km². The name is derived from the Swedish word for steps which refer to the step like hills forming the landscape of the region.

The Deccan Traps formed between 60 and 68 million years ago, at the end of the Cretaceous period. The gases released in the process may have played a role in the extinction of the dinosaurs. Before it was reduced to its current size by erosion and continental drift, it is estimated that the original area covered by the lava flows was as large as 1.5 million km². The volume of basalt is estimated to have been 512,000 km³.

It is postulated that the Deccan Traps eruption is associated with a deep mantle plume or hotspot. The plume or hotspot, known as the Réunion hotspot, is suspected of causing both the Deccan Traps eruption and opening the rift that once separated the Seychelles plateau from India. Seafloor spreading at the boundary between the Indian and African Plates subsequently pushed India north over the hotspot, which now lies under Reunion island in the Indian Ocean, southwest of India. The mantle plume model has, however, been challenged.

A large impact crater has been recently reported in the sea floor off the west coast of India. Called the Shiva crater, it has also been dated at 65 million years, right at the Cretaceous-Tertiary (K/T) boundary. The researchers suggest that the impact may have been the triggering event for the Deccan Traps as well as contributing to the acceleration of the Indian plate in the early Tertiary. However, opinion in the geologic community is not unanimous that this feature is actually an impact crater.Also, the reported age is in the middle of the ages given for the Deccan rocks.

The planet Venus is also thought to undergo vast basaltic flood eruptions, but on an even greater scale than those at Deccan Traps. It is not known whether the mechanisms are similar; Venus appears to lack Earth’s plate tectonics and its internal structure may differ in other ways as well.

The Reunion hotspot is a volcanic hotspot which currently lies under the Island of Reunion in the Indian Ocean. The Chaos-Cadillac Ridge and the southern part of the Mascarene Plateau are volcanic traces of the Reunion hotspot.

The hotspot is believed to have been active for over 66 million years. A huge eruption of this hotspot 66 million years ago is thought to have laid down the Deccan Traps, a vast bed of basalt lava that covers part of central India, and opened a rift which separated India from the Seychelles Plateau. The Deccan Traps eruption coincided roughly with the extinction of the dinosaurs, and there is considerable speculation that the two events were related. As the Indian plate drifted north, the hotspot continued to punch through the plate, creating a string of volcanic islands and undersea plateaus. The Laccadive Islands, the Maldives, and the Chagos Archipelago are atolls resting on former volcanoes created 60–45 million years ago that subsequently submerged below sea level. About 45 million years ago the mid-ocean rift crossed over the hotspot, and the hotspot passed under the African Plate.

The hotspot appears to have been relatively quiet from 45–10 million years ago, when activity resumed, creating the Mascarene Islands, which include Mauritius, Reunion, and Rodriguez. Mauritius and Rodriguez Ridge were created 8–10 million years ago, and Rodriguez and Reunion Islands in the last two million years. Piton de la Fournaise, a shield volcano on the southeastern corner of Reunion, is one of the most active volcanoes in the world, erupting last in February 2015.

The Reunion hotspot is a volcanic hotspot which presently lies under the Island of Reunion in the Indian Ocean. The hot spot is believed to have been active for over 65 million years. A huge eruption of this hot spot 65 million years ago is thought to have laid down the Deccan Traps, a vast bed of basalt lava that covers part of central India, and opened a rift which separated India from the Seychelles plateau. The Deccan Traps eruption coincided with the extinction of the dinosaurs, and there is considerable speculation that the two events were related. As the Indian plate drifted north, the hot spot continued to punch through the plate, creating a string of volcanic islands and undersea plateaus. The Laccadive Islands, the Maldives, and the Chagos Archipelago are atolls resting on former volcanoes created 60–45 MYA that subsequently submerged below sea level. About 45 MYA the mid-ocean rift crossed over the hot spot, and the hot spot passed under the African Plate.

The hotspot appears to have been relatively quiet from 45–10 MYA, when activity resumed, creating the Mascarene Islands, which include Mauritius, Reunion, and Rodriguez. Mauritius and Rodriguez ridge were created 8–10 MYA, and Rodriguez and Reunion islands in the last two million years. Piton de la Fournaise, a shield volcano on the southeastern corner of Réunion, is one of the most active volcanoes in the world, erupting last on August 13, 2004. So the emerged island represent 1/32 of the total mountain from the ocean floor 4000 m under the sea level, and even 1/100 with the part sunk.

An intro basaltic red bole horizon is studied for its weathering characteristics with respect to the
underlying and overlying basalts. The study indicates that all the three units have been considerably
weathered, the red bole unit, however shows some distinctive characteristics. The red boles show quite
higher cation exchange capacity (CEC) and lesser sodium adsorption ratio (SAR) and the organic carbon (OC) as compared to the weathered basalts. The lower values of Al2O3, TiO2 and Fe2O3(T) in
red boles indicate their lesser weathering than the underlying and overlying basalts, which is further
corroborated by the weathering intensity measured by the indices like chemical index of alteration
(CIA) and statistical empirical index of chemical weathering (W). It is also evident that the red bole
samples show more retention of original mafic and felsic components. While K2O is exhibiting an
erratic behavior the MgO and CaO do not show much leaching in red boles. Lesser leaching and
salinity in the red boles is indicated by the higher values of calcination and lower values of
salinization. The SiO2–Al2O3–Fe2O3 plot indicates that red bole samples are close to the basalt field
while weathered upper basalt is more kaolinized than the weathered lower basalt. These observations
reveal that the post formational weathering processes have least affected the original palaeo weathering
characters of the red bole horizon and hence the intro basaltic palaeosols (weathering horizons) can effectively be used to constrain the palaeo weathering and palaeo climates during the continental flood
basalt episodes in the geologic past.

Bole beds occur as prominent horizons composed of fine-grained clayey or earthy material having colors in shades of red to chocolate brown, green, purple or gray, often marking the flow contacts of Deccan basalts, which date to approximately 65 Ma. Bole beds preserved between two successive lava flows can be studied relative to soils developed into the same basalts during the Holocene. The bole beds have significantly lower electrical conductivity values and organic matter contents compared to modern soils. Results indicate that the bole beds may not have been subjected to intense weathering but nonetheless formed under uniform rainfall with surface runoff exceeding evaporation. The trace elements in red and green boles do not all show similar behavior with increasing weathering during their formation. Trace elements from the red and green boles inter trapped between the Deccan basalts have been studied to understand their mobility as they are characterized by distinct coloration. They have been correlated with the analysis of four underlying and nine overlying basalts and seventy two basalts occurring elsewhere in the Deccan Volcanic. During the formation of rocks like trap or basalt, the lava flows from the volcanoes spread on the available surface of the earth and settles for quite long geological years. Over a period of long time the lava flow recedes. The earth’s crust then gets deposited over lava flows (already got converted into either trap or basalt) before the next lava flows. During this long gap the earth’s crust gets converted into the so called Red or Green Bole depending upon the color they take up. Now the practical remedial measure is as follows:

Excavate the foundation of the igneous rock say e.g. the trap or basalt.
You may meet inter trapped bole of any color either red or green.
Check the quality and color of the bole layer
Excavate the entire quantity of red bole from the entire foundation area.
Now measure the thickness of the full bole layer.
Excavate the rock further below up to a depth equal to twice the thickness of the bole layer
Finally check the geological and physical qualities with soundness of the parent foundation rock.
Check for all other tests for foundation approval.
The foundation area is then ready for taking any further action.
The practical method of the construction of any dam over foundation where there are seams of some sorts of BOLES in the foundation arises when we strike any colored bole during foundation excavation. The depth of the bole needs to be checked before taking any decision to go further.

This actual work was taken up by me in the year 1979–80 at Bargi Damᐧ

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