Search on for Severed Head of Himalayas

By Vinit Wahi

The Himalayas are called Sagarmatha, meaning head of the sky. But its head itself is missing that too far away in the deep ocean- somewhere in the Bay of Bengal! The scientists are breaking their heads to find out this severed head which tumbled some time during the medieval age.

Himalayas being the mountain range that with 10 peaks soaring more than 8,000 meters above sea level, more than earns its nickname as part of the “rooftop of the world.” The missing head, in this case, describes the very first rocks to erode from the Himalayas, themselves uplifted as the Indo- Australian plate collided with and began subducting beneath the Eurasian plate in the early Cenozoic.

Those rocks washed out to sea over the course of millions of years as the Ganges and Brahmaputra Rivers flow from the Himalayas and transport about a billion tons of its eroded sediment into the Bay of  Bengal  every year. The  sediment forms and reforms the Bengal Fan, the largest submarine fan on the planet. No other deep- sea fan receives so much sediment, according to Hermann Kudrass, a marine sedimentologist at the University of Bremen in Germany.

In an interesting finding a team of geologists affiliated with multiple institutions in France and other countries have found evidence that a huge rockslide called its head had occurred in a part of the young Himalayas during the medieval era. Working in Nepal one team analysed features of the Sabche Cirque, a Himalayan basin and the same was reported in the journal Nature.

Even earlier research has shown that some mountains are too  tall to fall victim to the types of erosion that wear away shorter mountains. They are so tall that temperatures near the peak are always below freezing, for example, which prevents the cracking that accompanies freeze/ frost cycles in lower- altitude mountains. Such   mountains   are also too tall and steep to host  glaciers.  Instead, the researchers on this new effort argue, they collapse as rock slides. The big picture is  that the findings provide new evidence about how the planet’s highest peaks may evolve.

In fact, the study reveals glaciers can erode rock on the floors of mountain valleys but higher in the peaks, glaciers may just not form and year-round cold temperatures limit the freezing and thawing of ice that can break rocks, leaving open questions about how the highest mountains evolve over time. But these glaciers can still etch  away  at the lower slopes, making them steeper until the rock can collapse, possibly triggered by earthquakes. On human timescales, mountain peaks seem eternal. But on geological timescales, mountain peaks are ephemeral; their shape and altitude are constantly evolving in response to the competition between tectonic uplift and erosion, they further wrote.

As per the study , one team found the rocks to be breccias, that’s smaller rocks embedded in larger rocks. And excavating revealed that the size of the embedded rocks grew larger the deeper they were. They next broke open several of the rocks and carbon- dated plant material they found embedded inside. Subsequently, they also found that one of the peaks next to Sabche Cirque had experienced shearing along one of its faces, suggesting material had fallen from it into the valley below. The study further pointed out features of breccias indicated they were generated by a single rockslide granular avalanche.

Carbon dating of plant fossils in the rocks revealed they were all deposited at the same time, around 1200 CE. The researchers reached the conclusion that they came from 23 cubic kilometers of rock that slid from  a  mountain and buried the basin floor below a kilometer of rock. The evidence strongly suggests that a massive rock slide occurred sometime around 1200 CE, filling the valley below with debris up to a kilometer deep. The researchers suggest that prior  to the  rock  slide;  the peak from which it had occurred was likely over 8,000 meters high, implying it had lost approximately half a kilometer in height. The team even suggested that massive landslides like this one could shape other tall mountains.

They said findings shed light on one potential mode of evolution of high Himalaya peaks and their abrupt erosion by large rockslides. They have stressed upon the need for further studies to assess the erosive contribution of giant rockslides on the long-term topographic evolution of these mountain ranges. Previous work suggests that the Siang River (a section of the Brahmaputra) might have eroded the mountains to the point where all the missing rock caused some regions to rise faster than the rest of the range. The phenomenon is “kind of like a ‘tectonic aneurysm.

Meanwhile,  the  head of the Himalayas—and the secrets it may yet reveal—is still buried somewhere  beneath the waves of the Bay of Bengal, awaiting its own exhumation.

Ocean In Himalayas Mystery Within Mystery

Researchers at the Indian Institute of Science (IISc) and Niigata University, Japan, have discovered droplets of water trapped in mineral deposits that were likely left behind from an ancient ocean which existed around 600 million years ago in the Himalayas. Analysis of the deposits, which had both calcium and magnesium carbonates, also allowed the team to provide a possible explanation for events that might have led to a major oxygenation event in Earth’s history, Bengaluru- based IISc said in a release on Thursday.

“We have found a time capsule for paleo oceans,” says Prakash Chandra Arya, PhD student at the Centre for Earth Sciences (CEaS), IISc, and first author of the study published in ‘Precambrian Research’. Scientists believe that between 700 and 500 million years ago, thick sheets of ice covered the Earth for an extended period, called the Snowball Earth glaciation (one of the major glacial events in Earth’s history).

What followed this, it said, was an increase in the amount of oxygen in the Earth’s atmosphere, called the Second Great Oxygenation Event, which eventually led to the evolution of complex life forms. So far, scientists have not fully understood how these events were connected due to the lack of well-preserved fossils and the disappearance of all past oceans that existed in the Earth’s history, IISc noted, adding that exposures of such marine rocks in the Himalayas can provide some answers.

The deposits found by the team – which date back to around the time of the Snowball Earth glaciation – showed that the sedimentary basins were deprived of calcium for an extended period, probably due to low riverine input. The team hunted for these deposits across a long stretch of the western Kumaon Himalayas, extending from Amritpur to the Milam glacier, and Dehradun to the Gangotri glacier region.

Using extensive laboratory analysis, they were able to confirm that the deposits are a product of precipitation from ancient ocean water, and not from other places, such as the Earth’s interior (for example, from submarine volcanic activity). The researchers believe that these deposits can provide information about ancient oceanic conditions such as pH, chemistry, and isotopic composition, which have so far only been theorised or modelled.