Geology topics
Source-linked reports with geographic coverage including Mauna Loa.
Lava flows from Mauna Loa volcano, on the Island of Hawaiʻi, constitute a significant hazard to people and property. This report addresses those lava flow hazards, mapping 18 potential lava inundation zones on the island.
Mauna Loa is showing persistent signs of volcanic unrest. Since 2014, increased seismicity and deformation indicate that Mauna Loa, the volcano that dominates more than half of the island of Hawaiʻi, may be building toward its first eruption since 1984. Thousands of residents and key infrastructure are potentially at risk from lava flows, so a critical question is whether the volcano will follow patterns of previous eruptions or return to its now historically unprecedented 33-year slumber.
The Island of Hawai‘i is composed of five coalesced basaltic volcanoes. Lava flows constitute the greatest volcanic hazard from these volcanoes. This report is concerned with lava flow hazards on Mauna Loa, the largest of the island shield volcanoes. Hilo lies 58 km from the summit of Mauna Loa, the Kona coast 33 km, and the southernmost point of the island 61 km. Hawaiian volcanoes erupt two morphologically distinct types of lava, aa and pahoehoe. The surfaces of pahoehoe flows are rather smooth and undulating. Pahoehoe flows are commonly fed by lava tubes, which are well insulated, lava-filled conduits contained within the flows. The surfaces of aa flows are extremely rough and composed of lava fragments. Aa flows usually form lava channels rather than lava tubes. In Hawai‘i, lava flows are known to reach distances of 50 km or more. The flows usually advance slowly enough that people can escape from their paths. Anything overwhelmed by a flow will be damaged or destroyed by burial, crushing, or ignition. Mauna Loa makes up 51 percent of the surface area of the Island of Hawai‘i. Geologic mapping shows that lava flows have covered more than 40 percent of the surface every 1,000 years. Since written descriptions of its activity began in A.D. 1832, Mauna Loa has erupted 33 times. Some eruptions begin with only brief seismic unrest, whereas others start several months to a year following increased seismic activity. Once underway, the eruptions can produce lava flows that reach the sea in less than 24 hours, severing roads and utilities. For example, the 1950 flows from the southwest rift zone reached the ocean in approximately three hours. The two longest flows of Mauna Loa are pahoehoe flows from the 50-kilometer-long 1859 and the 48-kilometer-long 1880-81 eruptions. Mauna Loa will undoubtedly erupt again. When it does, the first critical question that must be answered is: Which areas are threatened with inundation? Once the threatened areas are established, we can address the second critical question: What people, property, and facilities are at risk? These questions can be answered by estimating the areas most likely to be affected by eruptions originating on various parts of the volcano. This report contains such estimates, based on the known source vents and areas affected by past eruptions. We have divided the volcano into potential lava inundation zones and prepared maps of these zones, which are presented here on the accompanying map sheets.
To test whether a catastrophic earthquake could affect an active magma system, mean abundances (adjusted for "olivine control") of titanium, potassium, phosphorus, strontium, zirconium, and niobium of historic lavas erupted from Mauna Loa Volcano, Hawaii, after 1868 were analyzed and were found to decrease sharply relative to lavas erupted before 1868. This abrupt change in lava chemistry, accompanied by a halved lava-production rate for Mauna Loa after 1877, is interpreted to reflect the disruptive effects of a magnitude 7.5 earthquake in 1868. This interpretation represents a documentable case of changes in magmatic chemical variations initiated or accelerated by a major tectonic event.
Flow-by-flow mapping of the 65 km long subaerial part of the southwest rift zone and adjacent flanks of Mauna Loa Volcano, Hawaii, and about 50 new 14C dates on charcoal from beneath these flows permit estimates of rates of lava accumulation and volcanic growth over the past 10 000 years. The sequence of historic eruptions along the southwest rift zone, beginning in 1868, shows a general pattern of uprift migration and increasing eruptive volume, culminating in the great 1950 eruption. No event comparable to 1950, in terms of volume or vent length, is evident for at least the previous 1000 years. Rates of lava accumulation along the zone have been subequal to those of Kilauea Volcano during the historic period but they were much lower in late prehistoric time (unpubl. Kilauea data by R. T. Holcomb). Rates of surface covering and volcanic growth have been markedly asymmetric along Mauna Loa's southwest rift zone. Accumulation rates have been about half again as great on the northwest side of the rift zone in comparison with the southeast side. The difference apparently reflects a westward lateral shift of the rift zone of Mauna Loa away from Kilauea Volcano, which may have acted as a barrier to symmetrical growth of the rift zone. -Author
In October 1978 (J.D. 286), the U.S. Geological Survey (USGS) established a seismic refraction line perpendicular to the Kona coast of Hawaii (Fig. 1). The purpose of the experiment was to define the crustal structure of the Kona coast and its relationship to the tectonics of Mauna Loa volcano. This open-file report describes the experiment and presents the data without interpretation. A similar experiment was performed earlier off the southeast coast of Hawaii. Those data are described in Zucca and others (1979) and the results presented in Zucca and Hill (1980).