Hualalai volcano's lava stratography has ventilation ash deposits with pahoehoe black basalt lava flows that were formed during 1800 to 1801 eruption. Five vents along the northwest fissure zone. Abundant xenoliths from ultramafic plutonic rocks. In eruptions, relatively gas-poor and fluid-rich magma fills the volcano's vent, increasing the amount of gas produced. They are considered viscous flows in this type of water, where groups of loose and sharp blocks cover most of the surface areas.
Occasionally, stratovolcanoes build in tens or hundreds of thousands of years, but all eruptive types generate highly explosive eruptions, especially basaltic andesite. Alkali-enriched, silica-deficient basaltic magma is the source of commonly porphyritic lava flows that erupt less frequently and in relatively negligible volume during a phase of declining and decaying activity in some Hawaiian volcanoes. No magma-related seismicity or soil deformation has been detected recently in Hualalai, making it difficult to say if and when the next eruption could occur. However, in 1929 an intense earthquake swarm hit Hualalai for a period of one month, which has been interpreted as due to an intrusion of magma near the surface, without a superficial eruption.
During this period, no microearthquake swarms or harmonic tremors (both indicative of magma migration) have been recorded, although Hualalai experiences several magnitude 4 earthquakes each year. The eruption depletes the supply of meltable magma in a given locality and, in the absence of more violent melting processes, leaves a stratum of crystalline refractory components. This magma may be available in batches that differ slightly in free silica content from batch to batch, both in the same and in different volcanoes; differentiation by fractionation of olivine does not occur within this primitive magma.
