Catálogo de publicaciones - libros

The space missions of the past decades have shown that impacts represent an ubiquitous phenomenon in the Solar System, and occur at all scales, from dust particles up to planetary bodies. In fact, a clue to the importance of this phenomenon also for our planet has always been available on the heavily cratered surface of the Moon, that testifies to the present and past fluxes of bodies on Earth crossing orbits.

Astronomical and geological investigations initiated in the past century have revealed that the Earth is continually subjected to the infall of a variety of solid solar system debris. Most of this debris is so small that it evaporates harmlessly, as it enters the Earth’s upper atmosphere at high speed. However, an occasional larger object survives atmosphere entry. Small examples of such objects result in meteorites on the surface of the Earth, with harmful consequences only for the rare individuals, who happen to be struck by them. More infrequent, but larger, objects can cause local or even global devastation. A recent report on the number and consequences of such impacts () proposes that the impact frequency can be computed as a function of the energy release, equal to the kinetic energy of the object before it strikes the Earth: where is the recurrence interval (in years) and is the energy release in megatons of TNT equivalent (1 MT = 10 cal ≈ 4.2 × 10 J).

The fossil record reveals that the evolution of life on Earth has been punctuated by a number of catastrophic events, of which one of the most devastating occurred at the end of the Cretaceous, approximately 66 million years ago. The postulate introduced in 1980 by Alvarez et al. (1980) that the collision of an approximately 10 km diameter asteroid with the Earth caused the extinction of the dinosaurs along with more than half of all plant and animal species has resulted in a greatly expanded research efforts in the area of catastrophic events ().

Tsunamis belong to the long-period oceanic waves generated by underwater earthquakes, submarine or subaerial landslides or volcanic eruptions. They are among the most dangerous and complex natural phenomena, being responsible for great losses of life and extensive destruction of property in many coastal areas of the World’s ocean. The tsunami phenomenon includes three overlapping but quite distinct physical stages: the generation by any external force that disturbs a water column, the propagation with a high speed in the open ocean and, finally, the run-up in the shallow coastal water and inundation of dry land (). Most tsunamis occur in the Pacific, but they are known in all other areas of the World including the Atlantic and the Indian oceans, the Mediterranean and many marginal seas. Tsunami-like phenomena can occur even in lakes, large man-made water reservoirs and large rivers.

There is a concern that the world we know today will end in a global ecological disaster and mass extinction of species caused by a meteorite impact (; ). We are aware that rare large impacts have changed the face of our planet as reflected by extinctions at the Permian/Triassic (∼251 Ma; ), Triassic/Jurassic (∼200 Ma; ) and Cretaceous/Tertiary (∼65 Ma; ) boundaries. Today astronomers can detect and predict the orbits of the asteroids/comets that can cause similar impacts. Yet, Tunguska, Meteor Crater-size and smaller meteorites that could cause local disasters are unforeseeable. However, while planning to avoid the next bombardment by cosmic bodies we can look at past interactions of human societies, environment and meteorite impacts to understand to what extent human cultures were influenced by meteorite impacts. The question is whether the past examples are relevant in the modern situation, but they are certainly useful. The Kaali crater field in Estonia, in that respect, is an excellent case study area for past human-meteorite interactions. Moreover, Kaali is not the only Holocene crater field in this region: in fact, during the last 10 000 years Estonia has been targeted at least by four crater forming impacts and there are five registered meteorite falls (Fig. 15.1). The two large craters, Neugrund and Kärdla, originate from 535 and 455 Ma, respectively (). cr]

The Earth’s atmosphere, ocean and land surface interact together to provide the environmental conditions to which life and society have become accustomed. Society has come to depend on these components working together to provide relatively stable (or at least regularly varying) and livable conditions that are conducive to growing and gathering necessary food, providing sufficient freshwater, limiting the domains and viability of disease vectors and, except on rare occasions, providing safe habitat for living and reproducing.

The nature of the bright bolide and the giant explosion that took place on June 30, 1908, in the Podkamennaya Tunguska river basin, Central Siberia, is still being discussed. The area with fallen trees is in excess of 2000 square km (), whereas the kinetic energy deposited by the impactor has been estimated to be ca. 15 million tons of TNT equivalent (or 1500 Hiroshima bombs; ). Nevertheless, Kolesnikov et al. (1973) have shown that the explosion could not be of nuclear nature. Its energy release was, in fact, too big to be a nuclear explosion. Two other nuclear hypotheses, one of annihilation and one of thermonuclear origin, have been tested by measuring Ar activity in rocks and soil at the explosion epicenter. No excess Ar was detected, and this method is much more sensitive than the method of measuring radiocarbon in tree rings (). Likewise no excess beta activity was observed in 1908, or the following years, in two ice cores from Camp Century nor in an ice core from DYE-3, all three on the Greenland ice sheet ().

In the early morning of 30 June 1908, a powerful explosion over the basin of the Podkamennaya Tunguska River (Central Siberia), devastated 2 150 ± 50 km of Siberian taiga. Eighty millions trees were flattened, a great number of trees and bushes were burnt in a large part of the explosion area. Eyewitnesses described the flight of a “fire ball, bright as the sun”. Seismic and pressure waves were recorded in many observatories throughout the world. Bright nights were observed over much of Eurasia. These different phenomena, initially considered non-correlated, were subsequently linked together as different aspects of the “Tunguska event” (TE).

Depending on distance from the event — at (101° 53′ 40″ E, 60° 53′ 09″ N) — the Siberian catastrophe of 30 June 1908 was reported as “” (barisal guns, brontides: Gold and Soter 1979) and/or “” followed by “”, also described as “lightning” and “thunderclaps”, after which an area of more than 2000 square kilometers, some 50 km, had its trees debranched, felled, or their tops chopped off, varying with their distance from the center and/or height above the valleys, even with islands of tree survival near the center, and in the valleys. A few tents (tepees), barns (storage huts), and cattle (reindeer) were damaged, hurled aloft, and/or . The haunting took some , variously reported between 2 min and an hour; one man even washed in the bath house to meet the death clean.

It is important to differentiate between a natural hazard and a natural disaster. A natural hazard is an unexpected or uncontrollable natural event of unusual magnitude that threatens the activities of people or people themselves (). A natural disaster is a natural hazard event that actually results in widespread destruction of property or causes injury and/or death. Only a very small fraction of the actual meteorite events are observed as falls in any given year. It has been predicted that 5800 meteorite events (with ground masses greater than 0.1 kg) should occur per year on the total land mass of the Earth. In a recent work, Cockell (2003) emphasizes the scientific and social importance of giving a coordinated and multidisciplinary response to events related with the entrance of small asteroidal bodies that could potentially collide with the Earth. In fact, it can be said that the recovery of small meteorites between 1 kg to 200 kg is relatively common; in Spain alone there are four meteorites in the collection of the National Museum of Natural History, weighing more than 30 kg (e.g. Colomera iron meteorite). But what would happen if the impact bodies, despite weighing up to 200 kg, would melt?