Kilauea is one of the most active volcanoes on Earth, dominating the southeastern part of the Island of Hawaiʻi. As a large shield volcano, its structure is broad with gentle slopes, created by the repeated outpouring of highly fluid lava. Kilauea is characterized by effusive eruptions, meaning the lava flows out rather than exploding violently. This style results from the low viscosity of its basaltic magma, shaping the hazards and consequences for the surrounding environment and communities.
Characteristics of Kilauea’s Lava Flows
The primary consequence of a Kilauea eruption is the massive volume of basaltic lava, which is hot and fluid. This low viscosity allows the molten rock to travel significant distances from the vent, often moving through insulated pathways called lava tubes. The temperature of the active flow core typically exceeds \(1,050^\circ\text{C}\).
The resulting lava fields are determined by two distinct flow textures, both referred to by Hawaiian names. Pāhoehoe lava has a smooth, billowy, or ropey surface that forms when the lava cools slowly beneath a thin crust. In contrast, ‘a‘ā lava has a rough, jagged, and clinkery surface composed of fragmented pieces of cooled crust.
The transition from pāhoehoe to ‘a‘ā occurs when lava cools more rapidly or is forced to move faster, causing the surface to tear and fold. While pāhoehoe flows are typically thinner, ‘a‘ā flows can be much thicker, sometimes reaching \(11\text{meters}\) in depth, and can surge at rates as great as \(33\text{meters per minute}\). This volume has historically destroyed homes, roads, and vegetation, reshaping the landscape in their path.
A specific hazard arises when the molten rock reaches the ocean, creating a corrosive plume known as laze (a contraction of “lava” and “haze”). This reaction generates plumes of steam, hydrochloric acid, and tiny particles of volcanic glass. These acidic plumes can irritate the eyes, skin, and respiratory tract for people near the coastal entry area.
Ground Instability and Landform Changes
The movement of magma beneath the surface causes substantial shifts in the volcano’s structure, resulting in ground deformation. Magma pushing through rift zones, such as the East Rift Zone, causes the ground to swell (uplift) or fracture. When magma drains from a summit reservoir, the ground above it can subside dramatically, leading to deep fissuring and collapse.
This subsurface movement is linked to the frequent occurrence of volcano-tectonic earthquakes. These seismic events are caused by stress changes from magma pressure and the seaward sliding of the volcano’s south flank, not by plate boundaries. Such earthquakes can be large, as demonstrated by the \(1975\) magnitude \(7.2\) event, which caused the entire south flank to slump downward and outward.
The eruption process is an agent of long-term geological change. When lava flows extend beyond the shoreline, they solidify to create new land, altering the coastline. Within the volcano, repeated collapse and refill cycles of the summit area contribute to the formation of large depressions known as calderas. Smaller, steep-sided pit craters and the complex network of lava tubes also form as a result of Kilauea’s activity.
Volcanic Air Pollution: VOG and Gas Emissions
Beyond the lava flows, Kilauea releases large quantities of volcanic gases that create a widespread atmospheric hazard. The primary gas emitted is Sulfur Dioxide (\(\text{SO}_2\)), along with water vapor and carbon dioxide. When \(\text{SO}_2\) is released, it reacts in the atmosphere with oxygen, moisture, and sunlight to form a hazy air pollution known as VOG, or Volcanic Smog.
VOG consists mainly of fine particulate matter, specifically sulfuric acid aerosols (\(\text{PM}_{2.5}\)), which scatter sunlight and create the visible haze. This air pollution can spread across the Island of Hawaiʻi and reach other islands depending on wind patterns. Exposure to both the \(\text{SO}_2\) gas and the fine particles causes acute health symptoms, including eye, nose, and throat irritation, headaches, and coughing.
Individuals with pre-existing respiratory conditions, such as asthma, are susceptible to the effects of VOG, which can cause narrowing of the airways and lead to increased hospital visits. The transformation of \(\text{SO}_2\) into sulfuric acid aerosols also contributes to acid rain. This acidic fallout can damage agricultural crops and vegetation downwind of the eruption sites.