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The Hawaiian Islands are known for their active volcanoes that frequently erupt in spectacular fashion, sending rivers of molten lava flowing down their mountainsides. But what causes this continual melting deep underground that produces the lava in the first place?
If you’re short on time, here’s a quick answer: The Hawaiian hot spot is caused by a plume of hot rock rising from deep within the Earth’s mantle, causing unusually high heat flow from below Hawaii that melts rock to produce magma and lava at the surface.
In this comprehensive article, we’ll explore the geology behind Hawaii’s lava in detail, including the Hawaiian hot spot, mantle plumes, plate tectonics, magma formation, and more. We’ll also look at how scientists study and model the complex processes driving Hawaii’s volcanism so they can better predict future activity.
The Hawaiian Hot Spot and Mantle Plumes
What is the Hawaiian Hot Spot?
The Hawaiian Hot Spot refers to a fixed hot region deep underneath the Pacific tectonic plate from which magma rises to form the Hawaiian island chain. As the Pacific plate slowly drifts northwestwards over this hot spot at around 32-35 miles per million years, the magma penetrates through the plate to erupt on the seafloor and form volcanoes.
This process has been ongoing for at least 80 million years, resulting in the Hawaiian-Emperor seamount chain stretching across the Pacific.
The Hawaiian Hot Spot is believed to originate from a narrow plume of hot mantle rock rising from the lower mantle around 1,800 miles deep in the Earth. These so-called mantle plumes bring heat from the Earth’s core to its surface in fixed locations, providing a continuous source of magma for eruption.
The plume theory helps explain the longevity and fixed nature of hot spots like Hawaii.
Evidence Supporting the Plume Model
There is substantial evidence supporting the mantle plume model as the driver of volcanic hot spots like Hawaii:
Alternative Theories
Some scientists have challenged the mantle plume model, proposing alternative mechanisms for hot spot volcano formation including:
| Cracks/Gaps | Fractures in tectonic plates enabling shallow melts |
| Edge convection | Small-scale convection cells at plate boundaries |
| Plate reheating | Frictional plate motion causing reheating |
However, most evidence favors the deep mantle plume theory with other processes potentially supplementing the volcanism. More research helps test predictions of mantle upwelling models against alternatives.
Understanding the geological processes behind the Hawaiian Hot Spot and its incredible chain of volcanoes remains an area of active investigation. But the plume model provides our best current framework for explaining Hawaii’s origins from deep inside our planet.
Plate Tectonics and Hawaiian Volcanism
The Movement of the Pacific Plate
The Hawaiian islands were created by a hot spot deep underground in the mantle layer. This hot spot produces magma that rises up through the plates on the Earth’s surface. Meanwhile, the Pacific tectonic plate is slowly moving northwest at a rate of about 7-9 centimeters per year.
This continual movement of the Pacific plate over the hot spot allows for the formation of the Hawaiian island chain over millions of years.
As the Pacific plate drifts across the hot spot, volcanoes form over the hot spot, build volcanic islands, become inactive and eventually erode back into the sea as they move beyond the hot spot. The oldest islands are at the northwest end of the chain next to the Aleutian Trench.
The southeastern islands are the youngest, with the Big Island of Hawaii currently positioned over the hot spot.
Interaction Between the Hot Spot and Plate Motion
The Hawaiian hot spot provides a continuous supply of magma from the mantle that punctures through the moving Pacific Plate. When the hot spot magma punctures through the plate at weaknesses in the crust, it can erupt through volcanoes onto the seafloor.
Over hundreds of thousands of years, the resulting underwater mountain can grow tall enough to emerge from the ocean as volcanic islands.
The Pacific plate keeps slowly moving over the hot spot during this time, forming a chain of islands. The active volcanoes on the Big Island are currently situated over the hot spot. The other islands were created as the plate moved northwest.
This is why the islands become progressively older and more eroded as you move along the chain toward the northwest.
The interaction between the stationary hot spot and the mobile plate forms a classic example of a mantle plume creating a line of age-progressive volcanic islands and undersea volcanoes like the Hawaiian-Emperor seamount chain.
As the Pacific plate continues to move, the Big Island’s active volcanoes will eventually go dormant. But the hot spot activity will continue with new underwater volcanoes forming southeast of Hawaii when magma erupts through the plate again in the future.
Magma Generation Beneath Hawaii
Partial Melting of Rock
The Hawaiian islands are located over a geological hotspot in the Pacific ocean where magma from the Earth’s mantle rises up to the surface. This magma is generated by the partial melting of rock in the mantle, which occurs due to high temperatures.
The rock begins to melt at around 1000-1300°C, creating pockets of magma that are less dense than the surrounding solid rock. Buoyancy causes this magma to then ascend up towards the surface.
The partial melting is likely caused by the upwelling of abnormally hot rock from the mantle transition zone around 410-660km deep. As this hot material rises, the decrease in pressure lowers its melting point, triggering melting of the rock.
Research shows that around 15-25% of the mantle rock partially melts to create Hawaiian magmas before they erupt at the surface as lava.
Ascent Through the Lithosphere
On the journey towards the surface, magma passes through the lithosphere – the rigid outer part of the Earth made up of the crust and upper mantle. Cracks and conduits in the lithosphere provide passageways that channel buoyant magma upwards beneath the Hawaiian islands.
As the magma rises, some of it collects and stalls in magma chambers under volcanoes. Here it evolves chemically, incorporating surrounding rock and crystallizing minerals until enough pressure builds up and it resumes its ascent.
Sophisticated seismic imaging reveals a complex network of magma chambers existing at around 5-15km depth beneath Hawaiian volcanoes.
Magma Storage and Evolution
| Location | Process |
| Lower Oceanic Crust | Primitive magma stalls and evolves |
| Moho Transition Zone | Further evolution and mixing |
| Shallow Crustal Reservoirs | Final storage prior to eruption |
As well as melting temperature and pressure, the chemical composition of magmas is changed by incorporating surrounding crustal rocks. For example, Hawaiian magmas become more silica-rich and alkaline as they assimilate gabbroic ocean crust and metasomatized lithosphere.
The extent of chemical evolution determines the explosiveness and characteristics of an eventual volcanic eruption. For instance, increased gas contents connected with the assimilation of crustal sulfur makes magmas more volatile.
Understanding these processes by analyzing solidified prior magmas enables us to better predict the course of future eruptions.
Ongoing Research and Predictions
Geophysical Imaging Methods
Scientists utilize advanced geophysical imaging techniques like seismic tomography, magnetotellurics, and satellite radar interferometry to peer deep into the interior of Hawaiian volcanoes. These methods create 3D models showing the pathways of magma and areas of partial melting in the mantle that feed eruptions (reference url: USGS article).
For instance, a 2022 study using seismic waves found a large hot spot of partial melting around 30 km underneath Kīlauea’s caldera that could indicate the next eruption location.
Computer Models and Simulations
Researchers build complex computer simulations of lava flows by integrating various datasets like topography, lava production rates, and thermal imagery. These models can now predict the most likely paths that lava flows will take during an eruption, like down Kīlauea volcano’s East Rift Zone.
Scientists further couple lava flow models with ashfall models to anticipate hazards. However, uncertainty still exists due to the natural complexity of volcanic systems.
Additionally, some research groups are using machine learning algorithms to detect patterns in decades of Hawaii eruption monitoring data. The goal is to improve short-term eruption forecasting by learning what subsurface signals tend to precede different types of eruptions.
A recent 2021 study achieved approximately 70% accuracy in classifying Kīlauea eruption types based on pre-eruption seismic and deformation data.
Forecasting Eruptions and Lava Flows
While the exact timing of Hawaiian eruptions is still unpredictable, monitoring networks like tiltmeters, gas sensors, and GPS stations allow scientists to detect accelerating subsurface magma movements that indicate an eruption is more likely in the coming days or weeks.
For example, Kīlauea’s 2018 eruption was preceded by a flurry of earthquakes as magma forced its way upwards and days of pronounced summit deflation.
Once an eruption starts, geologists use past behavior, current lava discharge rates, and topography to regularly update forecasts of lava flow extents and volcanic hazards. These forecasts now incorporate satellite data like thermal imagery along with ground observations.
Public warnings try to give affected communities as much advance notice as possible to protect lives and property.
Conclusion
The unique geology of Hawaii makes it one of the most active volcanic regions on Earth. Its volcanoes are fed by hot material welling up in a deep mantle plume that causes pressure release melting beneath the islands.
Advanced research techniques allow scientists to peer into Hawaii’s subsurface workings, model its complex behavior, and improve predictions about what areas may next erupt. While much has been learned, mysteries still remain about the exact origins and inner workings of Hawaii’s volcanic hot spot.
