Mystery of Siberia’s giant exploding craters may finally be solved (Image Credit: Space.com)
Eight giant, 160-foot-deep (50 meters) craters in the Siberian permafrost have baffled scientists since their discovery more than a decade ago — but a new theory may finally explain how they formed.
The craters are unique to Russia’s northern Yamal and Gydan peninsulas and are not known to exist elsewhere in the Arctic, suggesting the key to this puzzle lies in the landscape, according to a preprint paper published Jan. 12 to the EarthArXiv database.
Researchers have proposed several explanations for the gaping holes over the years, ranging from meteor impacts to natural-gas explosions. One theory suggests the craters formed in the place of historic lakes that once bubbled with natural gas rising from the permafrost below. These lakes may have dried up, exposing the ground beneath to freezing temperatures that sealed the vents through which gas escaped. The resulting buildup of gas in the permafrost may eventually have been released through explosions that created the giant craters.
But the historic-lake model fails to account for the fact that these “giant escape craters” (GECs) are found in a variety of geological settings across the peninsulas, not all of which were once covered by lakes, according to the new preprint, which has not been peer reviewed.
Previous studies have also linked the craters to accumulations of natural gas within the permafrost, but these can’t explain why the holes are only found in northern Russia. “Thus, the formation of GECs points to conditions specific for the Yamal and Gydan peninsulas,” researchers wrote in the preprint.
Permafrost on the Yamal and Gydan peninsulas varies widely in its thickness, ranging from a few hundred feet to 1,600 feet (500 m). The soil likely froze solid more than 40,000 years ago, imprisoning ancient marine sediments rich in methane that gradually transformed into vast natural gas reserves. These reserves produce heat that melts the permafrost from below, leaving pockets of gas at its base.
Permafrost in Russia and elsewhere is also thawing at the surface due to climate change. In places where it is already thin on the Yamal and Gydan peninsulas, melting from both ends and the pressure from the gas may eventually cause the remaining permafrost to collapse, triggering an explosion.
This “champagne effect” would explain the presence of smaller craters around the eight giant craters, as huge chunks of ice propelled out by the explosions may have severely dented the ground, according to the preprint.
There may also be more of these craters than we realize, the researchers added, as water and sediment likely filled some of the holes over time.
The release of natural gas and methane during these explosions could activate a climate feedback loop if global temperatures continue to creep up and accelerate permafrost melting.
“The formation of GECs has been connected to global climate change, with increasing summer and fall temperatures resulting in permafrost warming and degradation,” the researchers wrote.
An estimated 1,900 billion tons (1,700 billion metric tons) of greenhouse gas, including carbon dioxide and methane, are stored in the Arctic permafrost, according to the preprint. Growing emissions from thawing permafrost “are of great concern,” the authors added.
Siri ya maporomoko makubwa ya barafu ya Siberia yaweza kutatuliwa (Picha: Space.com) Maporomoko manane makubwa, yenye kina cha mita 50 katika barafu ya Siberia yamewashangaza wanasayansi tangu ugunduzi wao zaidi ya miaka kumi iliyopita, lakini nadharia mpya inaweza kueleza jinsi yalivyotokea. Mlipuko huo ni wa pekee katika peninsula za Yamal na Gydane kaskazini mwa Urusi na haujulikani kuwapo mahali pengine popote katika Arctic, ikidokeza ufunguo wa fumbo hili liko katika mandhari, kulingana na karatasi ya preprint iliyochapishwa Januari 12 kwenye hifadhidata ya EarthArXiv. Watafiti wametoa maelezo kadhaa kuhusu mashimo hayo kwa miaka mingi, kuanzia athari za meteor hadi milipuko ya gesi asilia. Nadharia moja inadokeza kwamba milipuko hiyo ilitokea mahali pa maziwa ya kihistoria ambayo wakati mmoja yalikuwa na gesi ya asili iliyokuwa ikitoka kwenye barafu ya milele. Huenda maziwa hayo yalitoweka, na hivyo ardhi chini yake ikawa na halijoto ya chini sana hivi kwamba mashimo ya hewa ambayo gesi ilitoka yalifungwa. Huenda gesi iliyokuwa imejikusanya katika barafu hiyo ya kudumu hatimaye ilitolewa kupitia milipuko iliyotokeza maporomoko makubwa ya ardhi. "Lakini mfano wa ""ziwa la kihistoria"" unashindwa kuelezea ukweli kwamba ""maji makubwa ya kutoroka"" (GECs) yanapatikana katika mazingira mbalimbali ya kijiolojia katika peninsulas, sio yote ambayo wakati mmoja yalifunikwa na maziwa, kulingana na preprint mpya, ambayo haijachunguzwa na wenzao." Uchunguzi wa awali pia umehusianisha maporomoko hayo na mkusanyiko wa gesi ya asili ndani ya barafu ya kudumu, lakini haya hayawezi kueleza ni kwa nini mashimo hayo yanapatikana kaskazini mwa Urusi tu. "Kwa hivyo, kuundwa kwa GECs inaonyesha hali maalum kwa Yamal na Gydan peninsulas", watafiti waliandika katika preprint. Permafrost katika peninsulas ya Yamal na Gydan hutofautiana sana katika unene wake, kuanzia mita mia chache hadi mita 1,600 (500). Inawezekana kwamba udongo huo ulifungika miaka zaidi ya 40,000 iliyopita, na hivyo kufungia matope ya kale ya baharini yenye metani ambayo hatua kwa hatua yaligeuka kuwa hifadhi kubwa za gesi ya asili. Hifadhi hizo hutokeza joto linaleyusha barafu ya kudumu kutoka chini, na kuacha mifuko ya gesi chini yake. Barafu ya kudumu katika Urusi na mahali pengine pia inayeyuka juu ya ardhi kwa sababu ya mabadiliko ya hali ya hewa. Katika maeneo ambayo tayari ni nyembamba kwenye peninsulas za Yamal na Gydane, kuyeyuka kutoka pande zote mbili na shinikizo kutoka kwa gesi inaweza hatimaye kusababisha permafrost iliyobaki kuanguka, na kusababisha mlipuko. "Hii ""athari ya champagne"" itaelezea uwepo wa maporomoko madogo karibu na maporomoko manane makubwa, kama vipande vikubwa vya barafu vilivyopigwa na milipuko inaweza kuwa imeharibika sana ardhi, kulingana na preprint." "Wanafunzi hao wanasema kwamba huenda kukawa na miamba mingi zaidi ya ile tuliyojua, kwa kuwa huenda maji na matope yalijaza baadhi ya mashimo hayo kwa muda.""" Kutolewa kwa gesi ya asili na methani wakati wa milipuko hii inaweza kuamsha mzunguko wa maoni ya hali ya hewa ikiwa joto la ulimwengu linaendelea kuongezeka na kuharakisha kuyeyuka kwa barafu ya kudumu. "Uundaji wa GEC umehusishwa na mabadiliko ya hali ya hewa ya ulimwengu, na kuongezeka kwa joto la majira ya joto na vuli kusababisha joto la permafrost na uharibifu", watafiti waliandika. Takriban tani bilioni 1,900 za gesi za chafu, ikiwa ni pamoja na kaboni dioksidi na methani, zimehifadhiwa katika barafu ya Arctic, kulingana na preprint. Waandishi hao waliongeza kwamba ongezeko la uzalishaji kutokana na kuyeyuka kwa barafu ya kudumu "linatia wasiwasi sana".