ILLUSTRATIONS FACING PAGE Thomas A. Jaggar _Frontis_ 1. Experimental Geology Laboratory, Harvard University, 1900 40 2. Fountain at edge of lava lake, May 17, 1917 41 3. Explosion cloud rising from Halemaumau, May 13, 1924 56 4. Crag in lava lake, January 23, 1918 57 5. Scientists of Technical Expedition to Aleutians, 1907 72 6. Captain George Seeley of the _Lydia_, 1907 73 7. Volcano House from Observatory, 1913 88 8. Island in Halemaumau lava lake, 1911 88 9. Hawaiian Volcano Observatory, 1912 89 10. Jaggar in seismograph vault beneath Observatory, 1916 89 11. Lava lake, showing bench, March 30, 1917 92 12. Halemaumau, showing lava lake and crags, December 8, 1916 92 13. Jaggar holding pipe for sounding lava lake, 1917 93 14. River of Alika flow, Mauna Loa, October 6, 1917 100 15. Lava streaming into a sinkhole in Halemaumau lava lake, July 7, 1917 100 16. Sakurajima Volcano, Japan, 1914 101 17. Fountain in lava lake, March 19, 1921 101 18. Isabel and Tom Jaggar in woods on Kilauea Volcano, 1923 120 19. Lava lake, fountains, and crags, March 20, 1921 121 20. Footprints in ash west of Mauna Iki 121 21. The _Honukai_ on Alaska beach, 1928 136 22. The _Ohiki_, first amphibian truck, 1928 136 23. Lava flow entering village of Hoopuloa, 1926 137 24. Lava flow of 1926 Mauna Loa eruption approaching Hoopuloa 137 25. Jaggar in office of Observatory in “Tin House,” 1937 152 26. Bomb bursting on lava flow, December 27, 1935 153 27. Fountain in Halemaumau lava lake, May 23, 1917 168 28. Rare dome fountain, Kilauea Crater, March 20, 1921 169 29. Lava stream near rim of Halemaumau, February 9, 1921 169 CHARTS Fluctuations of Halemaumau 113 Diagram of hypothetical globe section 179 PREFACE This, my latest book, is another experiment. After sixty years of volcanoes I have learned reversal of preconceived notions. Gradually I have learned a totally different approach.