Language
Click on the icons below to learn more about the hazards detailed in the 2020 Maui HMP.
A volcano is an opening in earth’s crust through which molten rock, called magma, and gases escape to the surface. Volcanoes form in three different types of tectonic settings: 1) subduction zone volcanoes are the most violent and destructive, and form where one tectonic plate is subducted under another; 2) rift volcanoes are the most common and form where two tectonic plates are spreading apart; and 3) hot spot are volcanic centers that are typically 60-120 miles across. Mount St. Helens, a Washington volcano famous for its eruption in 1980, is a subduction zone volcano, whereas the infamous Yellowstone Caldera is a hot spot.
Volcanoes can be active, dormant, or extinct. Active volcanoes are erupting or have erupted in recorded history. Dormant volcanoes are not currently erupting but are expected to erupt again in the future. Lastly, extinct volcanoes have not erupted in recorded history and are not expected to erupt in future. Volcanoes pose a variety of natural hazards.
Lava flows, domes, and dome collapses: Lava flowing across the ground rarely threatens human life, as it typically moves at a slow rate and follows a predictable path. Alternatively, sluggish, partially solidified lava may push up at the vent during an effusive eruption, creating a lava dome. A growing lava dome may become so steep that it collapses, violently releasing pyroclastic flows potentially as hazardous as those produced during explosive eruptions.
Pyroclastic flows: a pyroclastic flow is a ground-hugging debris flow of hot ash, pumice, rock fragments, and volcanic gas that can rush down the side of a volcano at a speed of 60 miles per hour or more. Temperatures in pyroclastic flows can be over 930 degrees Fahrenheit and are capable of burning and carbonizing wood. Distances pyroclastic flows can travel are dependent upon the surrounding topography and the volume of magma released.
Lahars: Lahars are another type of debris flow in which volcanic particles mix with water. Lahars are formed when pyroclastic flows enter rivers or creek systems, when they flow over snow and ice, or when heavy rain fall on loose volcanic debris. Lahars can travel as quickly as 100 miles per hour and travel as far as 190 miles. Lahar can also transition into normal floodwaters as they become diluted downstream.
Volcanic Ash and Tephra Fall: Explosive eruptions blast fragments and gas into the air with tremendous force. The finest particles (ash) billow upward, forming an eruption column that can attain stratospheric heights in minutes. Tephra (volcanic ash and larger rock fragments), carried by the prevailing winds, is an aviation hazard and may remain suspended for hundreds of miles before settling to the ground as tephra fall. Generally, tephra gain size and thickness of accumulations decreases with distance from the eruption.
Volcanic Gas or Fog (Vog): During an eruption, noxious gases, such as water vapor, carbon dioxide, sulfur dioxide, hydrogen sulfide, carbon monoxide, and chlorine, can be released into the surrounding area. These gases can mix with atmospheric moisture to produce volcanic smog (vog) and acid rain. Vog poses a health hazard, as it can result in respiratory illnesses, contaminated water, and crop damages. In rare cases deaths and injuries can result gases released as part of an eruption. Perhaps the most tragic incident to occur in recent history is that in 1986 at Lake Nyos, Cameroon, in which over 1,700 people died from lack of oxygen when large amounts of carbon dioxide spilled out of Lake Nyos and flowed down to a nearby village. Further, when molten lava flows into the ocean, it creates localized air pollution known as laze (combination of the words lava and haze). This is a type of gas plume that results in hazy and noxious conditions downwind of an ocean entry. It forms through a series of chemical reactions as hot lava boils seawater. The plume is a mixture of hydrochloric acid gas (HCl), steam, and tiny volcanic gas particles. The entry point area and downwind should be avoided by humans, as laze can cause skin and eye irritation, and breathing difficulties.213 Laze was formed in the most recent eruption of Kilauea in 2018.
Maui County is at risk to two different types of volcanic hazards – lava flows and vog. Lava flows pose a risk only to the Island of Maui, from a possible eruption of Haleakalā. Haleakalā is a shield volcano, with a moderate threat level designation from USGS.
On the Island of Hawaiʻi, lava-flow hazards are rated on a scale of one through nine, with one being the zone of highest hazard and nine being the zone of lowest hazard. For example, the summits and rift zones of Kilauea and Maunaloa volcanoes are rated Hazard Zone 1. Using this same scale, preliminary estimates of lava-flow hazard zones on Maui were made in 1983 by the U.S. Geological Survey. In 2006, researchers suggested an adjustment of the zones in relation to Haleakalā due to the Maui volcano’s considerably smaller size than the active volcanoes located on the Island of Hawaiʻi. As a result, these researchers suggested that Maui Zone 1 is roughly equivalent to Hawaiʻi Island Zone 3, Maui Zone 2 is roughly equivalent to Hawaiʻi Island Zone 4, and Maui Zone 3 is roughly equivalent to Hawaiʻi Island Zone 6. In other words, no place on Maui has volcanic hazards equivalent to Lava-Flow Hazard Zones 1.
The second volcanic hazard, vog, has the potential to impact the entire county. In the Hawaiian Archipelago, potential sources of vog are Haleakalā on the Island of Maui, Maunaloa and Hualalai on the Island of Hawaiʻi, and the active Kilauea volcano, also on the Island of Hawaiʻi. Of these volcanoes, only Kilauea has had an eruption in the last 200 years.
Kilauea’s most recent eruption initiated in 1983 and continues to the present day. From Kilauea, vog typically originates at the Halemaumau vent (at the volcano’s summit), the Puu Oo vent (at the volcano’s upper east rift zone), and the ocean entry plume (along the shoreline of Puna District). The concentrations of sulfur dioxide gas in vog are typically greater near Kilauea. Sulfur dioxide levels are lessened further away or upwind from the vents. While vog typically impacts the Island of Hawaiʻi, during episodes of Kona storms or non-trade wind conditions, vog can be transferred further north towards the Maui County. Because of Maui Island’s unique topography, vog is funneled through the central valley between Haleakalā volcano and the West Maui Mountains. Therefore, the effects of vog are not limited to the island’s southern coast in Kīhei-Mākena but can extend as far as the agricultural areas of central and upcountry Maui and the densely populated areas of Wailuku and Kahului on the island’s northern shore. Episodes of vog on the islands of Lānaʻi and Molokaʻi are less common because these islands are further away from the sources on the Island of Hawaiʻi. Lānaʻi and Molokaʻi are also shielded from wind-blown vog by the mountains on Maui Island.
Haleakalā has erupted approximately 10 times over the last 1,000 years, with the most recent eruption around 1790 on the volcano’s south flank. At the time of the eruption, this area of the island was not populated.
More recently, vog episodes have impacted Maui County from eruptions of neighboring Hawai’i island. Significant vog occurrences in Maui County have included the following:
April 25, 2008: According to The Maui News, the Island of Maui District Health Office issued an advisory for the residents of the Island of Maui due to vog originating from Kilauea’s summit vent. The advisory urged individuals with respiratory conditions to take precautions. The Hawaiian Volcano Observatory reported that a few days before the advisory for the Island of Maui went in effect, sulfur dioxide levels around the observatory topped 1 ppm for a period of 2 hours.
January 2015: Maui County experienced obscured views and potentially hazardous vog conditions. A surface ridge sitting over the islands changed the typical trade wind weather pattern, forcing winds to come up from the south, instead, bringing along vog from Hawai’i island's Kilauea Volcano up as far as Kauai. The vog was so thick, that a kayaker became disoriented while trying to paddle from Maui to Hawai’i island and had to be rescued by the Coast Guard 19 miles northeast of Kohala.
May 2018: New eruption at Kilauea began, lasting through August 2018. Maui County experienced potentially hazardous vog conditions associated with this eruption.
The extent of the hazard posed by volcanic gases and vog depends on the amount of magma being erupted and the concentration of gas in that magma. The Hawai’i Department of Health has developed an index reflecting the hazardous levels of sulfur dioxide, a common noxious gas present in vog. These color-coded categories are presented in the figure above. Based on past events and information from the International Volcanic Health Hazard Network, the most severe vog conditions expected for Maui County is the orange, indicating that sulfur dioxide levels are unhealthy for sensitive groups, such as the elderly, very young, or those with respiratory illnesses.
Future Probability
Based on past events, Maui experiences a lava flow event from an eruption at Haleakalā every few hundred years. However, the county typically experiences a vog event due to eruptions on the Island of Hawaiʻi every few years. Within Maui County, certain community planning areas are more likely to experience volcanic hazards than others due to potential lava flow trajectories or wind patterns that bring vog from the Island of Hawaiʻi to Maui County.
All of Maui County is vulnerable to volcanic hazards from vog. While lava flows are slow-moving, they destroy essentially everything in their path. Therefore, all current and future buildings, infrastructure, critical facilities, and populations within lava flow hazard zones are considered at risk to lava flow.
Buildings and Infrastructure: All buildings and infrastructure (including critical facilities) within lava flow hazard zones are considered at risk. This includes the Pāʻia-Haʻikū, Makawao-Pukalani-Kula, and Hāna community planning areas, as well as the eastern portions of the Kīhei-Mākena and Wailuku-Kahului community planning areas.
All buildings and infrastructure in Maui County are also considered at risk to vog. While most vog impacts are on human health, vog can impact buildings and infrastructure through corrosion. Acid aerosols increase corrosion to any exposed metal along the path of the downwind vog plume, including fencing, waterlines, water tanks, farm equipment, and exposed steel structures (i.e. transmission towers, bridges). Even in relatively dry downwind areas, severe corrosion will generate significant economic losses. Dew formation drives corrosion rather than infrequent rainfall; during the evening hours, as the dew point temperature is approached, acid aerosols will form an extremely corrosive film on metallic surfaces. With daily replenishment of fresh acid from vog, and nightly condensation of moisture it is reasonable to anticipate substantially more rapid deterioration of exposed metal surfaces than would occur in similar environments not exposed to vog.
Health and Safety: It can be assumed that all existing and future populations are at risk to volcanic hazards. Injuries and fatalities are possible people within lava flow trajectories due able not able to evacuate in time. Further, vog can have significant impacts on health and life safety, especially for populations considered to have increased vulnerability.
Sulfur dioxide is irritating to the eyes, nose, throat and respiratory tract. Short-term exposure to elevated levels of sulfur dioxide may cause inflammation and irritation, resulting in burning of the eyes, coughing, difficulty in breathing and a feeling of chest tightness. In terms of exposure to vog, sensitive populations include young children and individuals with preexisting respiratory conditions, such as asthma, emphysema, bronchitis, and chronic lung or heart disease. Individuals who belong to these sensitive populations may respond to very low levels of sulfur dioxide in the air. Prolonged or repeated exposure to higher levels may increase susceptibility to vog impacts.
Economic Impacts: Economic impacts from volcanic hazards could include loss of buildings or infrastructure associated with lava flows. Other impacts from both lava flows and vog episodes include business interruptions and potential impacts to tourism.
Climate Change Impacts: Climate change does not have any known impacts on the frequency or intensity of volcanic hazards in Maui County. It is possible that changes in trade wind patterns could impact vog events. Further, greenhouse gases released during volcanic eruptions are likely to contribute to climate change.
