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Characteristics of cosmic-ray hadronic interactions in the l00_1017 eV range are studied by observing a total of 429 cosmic-ray families of visible energy greater than 100 TeV found in emulsion chamber experiments at high mountain altitudes, Chacaltaya (5200 m above sea level) and the Pamirs (4300 m above sea level). Extensive comparisons were made with simulated families based on models so far proposed, concentrating on the relation between the observed family flux and the behaviour of high-energy showers in the families, hadronic and electromagnetic components. It is concluded that there must be global change in characteristics of hadronic interactions at around l0b~eV deviating from those known in the accelerator energy range, specially in the forwardmost angular region of the collision. A detailed study of a new shower phenomenon of small-pT particle emissions, PT being of the order of 10 MeV/c, is carried out and its relation to the origin of huge "halo" phenomena associated with extremely high energy families is discussed as one of the possibilities. General characteristics of such super-families are surveyed.

Characteristics of γ -ray families with halos (XREC, Pamir) and data of experiments with EAS are analyzed to estimate the proton and helium (p+He) fractions in the primary cosmic radiation at E 0 = 1-100 PeV. It is shown that at energies E 0 ∼ 1-100 PeV the fraction of p+He remains significant, namely, the fraction of p+He is near 40% at E 0 = 10 PeV.

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Here we present a summa~ of joint discussions on the results of three mountain experiments with large-scale emulsion chambers, at Pamir, Mt. Fuji and Chacahaya. Observations cover gamma quanta, hadrons and their clusters (called "families").The following topics are covered, concerning the characteristics of nuclear interactions the energy region 1014-1016 eV: (i) rapid dissipation seen in atmospheric diffusion of high-energy cosmic-rays; (i.i) multiplicity and Pt increase in produced pi-mesons in the fragmentation region; (iii) existence of large-P t jets, (iv) extremely hadron-rich family of the Ccntauro type: (v) exotic phenomena in the extremely high energy region beyond 1016 eV.

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