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On January 12–13, 1960, a twelve‐man expedition visited Anak Krakatau to record its renewed activity. Explosive, vulcanian‐type eruptions of pyroclastics from fine ash to blocks 2 meters in diameter occurred at ½‐ to 10‐minute intervals throughout the period of observation. A cyclic repetition of approximately twenty small, turbulent, explosion clouds of gas and ash rising 150 to 300 meters alternated with four to six larger eruptions of gas, ash, and lapilli clouds turbulently rising to 1200 meters, the latter accompanied by larger blocks landing as far as 600 meters from the vent. A new topographic survey was completed, and four maps showing Anak Krakatau's growth since 1950 are presented. Recent fathometer measurements show the total size of Anak Krakatau and suggest that the 1883 caldera floor is being gradually leveled with volcanic detritus. Seismic records indicate that the eruptions begin at approximately 200 meters below sea level and churn their way to the surface. Steam generation where the magma reaches the porous, pyroclastic base of Anak Krakatau is considered an important contribution to the periodic gas explosions. Energy released in individual large explosive eruptions is estimated to be 170 tons of TNT equivalent. Over 20‐minute increments, the rate of energy release is nearly constant at 3.1×1013 calories, or 31,000 tons of TNT equivalent, per day. The present composition of the ejecta is still basaltic, and, although no danger of further collapse is indicated, more systematic observation of the renewed activity is warranted for scientific purposes.

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