Barriers to Protect Hilo from Lava Flows'

THE CITY OF HILa, on the island of Hawaii, lies on the flank of one of the world 's most active volcanoes, Mauna Loa. For more than a century the danger of destruction of the city by lava flows has been recognized. Old documents recount the apprehension with which Hilo residents watched the advance of the lava flows of 1852 and 1855. In 1881 concern was even greater, as the flow front crawled within a mile of the shore of Hilo Bay. Early in his studies of Hawaiian volcanoes, the late Dr. Thomas A. Jaggar recognized the threat to Hilo, and for many years the safety of the city and methods by which it might be insured were among his principal concerns (Jaggar , 1931, 1949). In 1937, following preliminary studies by the staff of the Hawaiian Volcano Observato ry, Jaggar proposed the building of a barrier, or barriers, on the lower slopes of Mauna Loa to deflect lava flows from Hilo harbor and its immediate vicinity. Such a barrier would consist essentially of a great wall stretching diagonally across the slope. The purpose of the barrier would not be to hold back the flow, like a dam, but to turn the flow and direct it away from the vital area. In 1938 a study of the project was begun by the U. S. Engineer Department (now U . S. Army, Corps of Engineers). A route and design for the barrier were chosen, and the entire proposal was subjected to careful study. It was found in the estimate of the Engineer Department to be entirely feasible. The official report, in January 1940, stated: " The District Engineer believes it is possible to protect the harbor and city by a properly located and constructed barrier. " The construction of the barrier was not carried