How ever, the period when the strait was formed is somewhat contradicted by an intriguing account in an early Javanese chronicle The Book of Kings. It states that in the year 416 AD the mountain Kapi (Krakatau) burst into peaces and sunk into deepest of the earth and the sea flooded the land from Gunung Gede near Bogor to mountain Raja Basa in Southern Sumatra. The chronicle concludes: After the waters subsided the mountain Kapi and surrounding land became sea and the island of Java was divided into two parts.
It is a curious fact that no sea straits between Sumatra and Java was known before 1.100’s by the far ranging Chinese and Arabian traders and later European explores.Beneath the mountains and forest of Ujung kulon, carved by the thousands of centuries of rain, wind and sea, are foundation of the land – a young mountain system formed over the older strata of the Sunda Shelf. Geologically, the Ujung kulon Peninsula, Gunung Honje Range and Panaitan Island are part of this young tertiary mountain system while the central part of Ujungkulon is of older limestone formations which have been covered by alluvial deposits in the north and sandstone in the south. Much of underlying rocks and early soils of the park are covered by volcanic ash, in places up to 1 meter deep, a legacy from the Krakatau eruptions.
The mountain ranges were all formed by the same folding event in the Miocene period creating beneath the forest of the Gunung Honje Range an eastward tilting mountain block. A reminder of this activity is a geological fault line situated off the Tamanjaya coastline. It bisects the park beneath the isthmus as it passes through the Sunda straits connecting the volcanic islands of Krakatau to the major tectonic fault line to the south of Indonesia
Ujung kulon’s tropical maritime climate, somewhat cooler than inland areas of Java, produces an annual rainfall of approximately 3.250 mm. Temperatures range between 25º and 30ºC, with a humidity level generally between 80% and 90%. April to October are the drier months, particularly between July to October. During these months there are long period of fine, calm weather with occasional spells of overcast skies, rain and rougher seas. The wetter season usually begins in November and finishes in March bringing an average of 400 mm of rain per month. The heaviest rains of December and January are often accompanied by squalls and strong winds, clearing the atmosphere and producing brilliant sunsets and spectacular panoramas