A fresh look at catastrophic impact-cratering: how do melt-bearing impact-deposits form?

Lead Research Organisation: University of Leicester
Department Name: Sch of Geog, Geol & the Environment

Abstract

When asteroids collide with Earth they shock the crust causing the target area to vaporize, melt, and fragment in seconds. Vast quantities of searing-hot melted rock, rock-fragments and dust are ejected through the atmosphere, leaving craters <300 km across and draping the surrounding landscape with debris. This, and the attendant catastrophic air blasts, earthquakes and tsunami, devastate the environment, biota and ecosystems. Impacts change climate, cause global mass-extinctions, and arguably represent the greatest natural hazard to humanity. They have actually shaped Earth history and they produce diamonds and useful sources of precious metals. Its therefore surprising that fundamental aspects of the process are not understood: until we better understand what happens near the point of impact we won't properly understand the wider effects.
Luckily there hasn't been a recent large impact, so our understanding has to be pieced together from forensic-style investigations of the products of old ones. Impact craters on Earth are really important as they provide hands-on access to internal structures, the ejecta deposits and the melt-fragments and minerals that yield vital clues to help reconstruct the extreme events.
We will investigate how hot impact-melt is fragmented and transported rapidly across the landscape from the impact site. Deposits known as 'suevite' and 'impact-melt breccia' have proved immeasurably useful, telling us much of what we have learned about impacts, e.g the phenomenal high pressures involved. Yet surprisingly impact-melt fragmentation and transport remains one of the least-understood and controversial aspects of impact-cratering. Scientists who study volcanoes have long been tackling how hot melt breaks and how the resultant melt fragments are ejected across the landscape. They have developed increasingly sophisticated field and laboratory approaches to take-apart evidence preserved in deposits. Yet astonishingly such methods have not yet been adapted for the study of asteroid impacts. Impacts clearly differ from volcanoes (e.g. the initial temperatures and pressures) but melt fragmentation and transport must follow the same laws of physics. We propose to bring together, for the first time, world-leading physical volcanologists and impact-specialists, to integrate state-of-art approaches to improve understanding and to spearhead a new wave of research that will transform the field.
Focusing on Earth's best-preserved large impact-crater, Ries (Germany) and selected other sites, we will reappraise impact-melt bearing rocks to determine, with fresh eyes, the processes they reveal. We will adapt 3 state-of-art methods from volcano-investigations: 1. the fine-art study of examining internal variations in subtle layering and grain sizes in granular rocks to reveal how the particles were transported and deposited from high-velocity ground-hugging density currents; 2. how the shapes and patterns of bubbles in glass shards produced by the fragmentation of visco-elastic melt - like rapidly-stretched custard - can be used to reveal the physical properties of the hot melt when it broke apart; and 3. how orientations (unpicked using rock-magnetism) preserved in deposits of catastrophic currents can be used to reveal hitherto-hidden information about how the impact-crater slopes morphed and shifted just after the initial impact through to the final stages of gravitational collapse and cooling. The work is very timely given the current state of flux in this field, and because it will draw on the very latest experimental data from volcanology, computer-simulations of impacts, a 2017 geophysical survey (Ries) and 2017 borehole (Chicxulub). From the results we will reconstruct how hot impact-melt behaves and moves as the developing impact-crater subsides. This will improve our understanding of how impact craters are created, and how hot material is transported across the planet, causing immense environmental damage.

Planned Impact

Large asteroids hitting Earth - and the likely dramatic consequences - captures the public imagination, and makes an excellent vehicle to communicate to the public a fascination for science and the natural world.
We will do this through a short film, animation and interactive exhibits in close collaboration with two UNESCO Global Geoparks, selected UK and European museums and the globally acclaimed University of Leicester Museum Studies Department
As laid out in our Pathways to Impact Plan we will engage with several public museums and geoparks to bring new ideas to the general public, incliuding potentially controversial information and drawing attention to future scientific challenges. To do this, we have approached the National Space Centre (Leicester), the Museum für Naturkunde (Berlin), the RiesKraterMuseum (Nördlingen), Northwest Highlands Geopark (Scotland), Spaceguard Centre (Wales), and Ries Crater Geopark (Germany). Furthermore, we have links to the Natural History Museum in London and the Discovery Centre in Edinburgh to also develop ideas with them.

Who could benefit, and how, from our collaborative Impact Plan?
1. Geoparks and Museums in the UK and abroad will benefit by enhanced popular exhibits and new interactive technologies.
2. The general public, who attend and learn from from new exhibits and activities at museums.
3. Audiences at public events (geoparc tours, lectures and other events in museums) will benefit through engagement with 'front-line' researchers.
4. School pupils, by engaging in a popular, lively science subject, that can draw them into other areas of science.
5. Colleges and universities could benefit by the general population maintaining an interest in science.
6. Local communities in the remote Assynt (Scotland) may benefit through tourism-related income, following the enhancement and development of their geopark and visitors centre.
7. Rural communities around the Ries Crater in Germany similarly should benefit from the Geopk, drawing visitors to the countryside and not just the main towns.
8. And the rural Spaceguard Centre in Wales could benefit from enhanced involvement with local schools and visitors.
9. The scientists involved in the Pathways to Impact Plan would benefit through the presentation of activities to the public, as such activities keep their research fresh and invigorated.
10. Technology developers, app-designers and 3D specialists would enjoy the challenge of transforming ideas of what happens during a large impact event to the digital world for visualisation.

Publications

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