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Fluids associated with the San Andreas and companion faults in central and south-central California have high 3 He/ 4 He ratios. The lack of correlation between helium isotopes and fluid chemistry or local geology requires that fluids enter the fault system from the mantle. Mantle fluids passing through the ductile lower crust must enter the brittle fault zone at or near lithostatic pressures; estimates of fluid flux based on helium isotopes suggest that they may thus contribute directly to fault-weakening high-fluid pressures at seismogenic depths.

The sudden, catastrophic release of gas from Lake Nyos on 21 August 1986 caused the deaths of at least 1700 people in the northwest area of Cameroon, West Africa. Chemical, isotopic, geologic, and medical evidence support the hypotheses that (i) the bulk of gas released was carbon dioxide that had been stored in the lake's hypolimnion, (ii) the victims exposed to the gas cloud died of carbon dioxide asphyxiation, (iii) the carbon dioxide was derived from magmatic sources, and (iv) there was no significant, direct volcanic activity involved. The limnological nature of the gas release suggests that hazardous lakes may be identified and monitored and that the danger of future incidents can be reduced.

1. Catechol was metabolized through 2-hydroxymuconic semialdehyde by cell-free extracts of benzoate-grown Azotobacter strains. Some properties of catechol 2,3 oxygenase preparations from Azotobacter vinelandii 206 are described.2 . Two different enzymatic activities able to attack 2-hydroxymuconic semialdehyde have been found in crude extracts from benzoate-grown cells ; one catalyses a hydrolytic release of formate from the semialdehyde and the other a dehydrogenation of this compound to 4-oxalocrotonate. However, the low, non-inducible levels of 2-hydroxymuconic semialdehyde hydrolase activity appear negligible for metabolic purposes and the semialdehyde seems to be dissimilated almost exclusively via 4-oxalocrotonate, by the action of a NAD+-dependent dehydrogenase, in Azotobacter strains.3, A tautomerase activity responsible for the interconversion of the enol and keto forms of 4-oxalocrotonic acid was found in extracts from benzoate-grown cells.4. 4-Oxalocrotonate was stoicheiometrically converted to CO, and 4-hydroxy-2-oxovalerate by a partially purified extract, with the transient formation of a compound that appears to be 2-oxopent-4-enoic acid. The 4-oxalocrotonate decarboxylase activity was stimulated by Mg2+ or Mn2+ ions and was inhibited by EDTA.5. Cell-free extracts from Azotobacter strains converted synthetic 4-hydroxy-2-oxovalerate to acetaldehyde and pyruvate.6. A reaction sequence, termed the 4-oxalocrotonate pathway, for the dissimilation of catechol to acetaldehyde and pyruvate by Azotobacter species is presented. All the enzymes operative in this pathway were inducible, except the 4-hydroxy-2-oxovalerate aldolase. 7. The findings described here are discussed in connection with the two previously reported meta cleavage pathways for the oxidation of catechol in Pseudomonas strains.