What is causing Hawaii's hotspot to heat up? Photo Credit: USGS via Wikipedia

Hawaii’s Hotspot Heats Up

NGSS Standards: 

  • MS-ESS2-2. Construct an explanation based on evidence for how geoscience processes have changed Earth’s surface at varying time and spatial scales.
  • MS-ESS2-3. Analyze and interpret data on the distribution of fossils and rocks, continental shapes, and seafloor structures to provide evidence of the past plate motions.

Key Vocabulary: volcano, eruption, magma, lava, hotspot, tectonic plate, island chain, seamount, fissures, harmonic tremors

Hotspot Article Guide

The volcanic activity comes to no surprise as Kilauea sits above the Hawaiian hotspot. Scientists have been studying and monitoring Kilauea for years trying to better understand how volcanoes operate in hopes of being able to better predict when eruptions will occur and to lessen the impact on humans.

Over the last couple weeks, Kilauea, one of the volcanoes on the Big Island of Hawaii and one of the world’s most active volcanoes, has heated up. There have been almost two dozen eruptions in Kilauea’s East Rift Zone and explosive eruptions from Kilauea’s main crater. Since May 3, eruptions have been spewing lava into residential areas, destroying homes, roads, and numerous other structures. These eruptions are a result of an increase in pressure of the magma chamber that fuels the volcano in addition to the intrusion of magma into the side of the volcano.

Aerial View of one of the fissure eruptions. Video Credit: USGS

What’s a hotspot?

A hotspot is an area of volcanic activity at a relatively stationary location. What makes hotspot volcanism unique is that it does not occur at the boundaries of Earth’s tectonic plates, where most other volcanoes are located. Instead, volcanism occurs at abnormally hot centers within tectonic plates as a result of a mantle plume. Mantle plumes act like a stream of heated lava rising in a lava lamp where they represent the rising of extremely hot rock within the Earth’s mantle. Like the lava lamp where the lamp is heated at the base by the light bulb, the mantle is heated at its base by Earth’s outer core causing the warmer (less dense) mantle rocks to rise. The intense heat from the mantle plume and the lower pressure it undergoes as it rises, melts the bottom of tectonic plates and creates magma, which rises through cracks in the tectonic plates and erupts to form volcanoes.

However, the volcanoes above a hotspot do not erupt forever. As the tectonic plate moves over the hot spot, eventually the volcano will be cut off from the magma source and become dormant. Meanwhile, a new volcano will form over the hotspot where the older volcano once was. Over millions of years, a line of volcanoes forms, along which their age increases with distance from the hotspot. Geologists can estimate the age of the volcanoes by using hotspots as a fixed reference; the further a volcano is from the hot spot, the older it is.

Diagram showing evolution of volcanic islands formed by a hotspot. Seamounts are underwater volcanoes that have not yet breached the water surface yet or are now dormant volcanoes. Photo Credit: Science Over Everything

The Hawaiian Islands are a classic example of this line of volcanoes. The Islands are part of the Hawaiian-Emperor chain which includes volcanoes and seamounts that have developed over 70 million years, indicating that the hotspot has been here for a very long time. The youngest island, the Big Island, is actually made up of 5 volcanoes. Just to the southeast of Big Island, a new seamount is forming, Lōʻihi, which over the next few hundred thousand years will be the newest Hawaiian island.

Map of the Hawaiian-Emperor island and seamount chain.
Photo Credit: Ingo Wölbern via Wikimedia

So what’s causing all these eruptions?

Earlier this year, geologists began seeing warning signs that the pressure inside the magma chamber under Kilauea was increasing. The island’s most active volcano has two areas where it is splitting apart, one extending to the east and one to the southwest of the main crater. These areas are called rift zones, and allow for the intrusion of magma into the slope of the volcano itself. In 1983 volcanic eruptions localized to a vent along the East Rift Zone and quickly built up into a volcanic cone, called Puʻu ʻŌʻō, that has been erupting nearly continuously ever since, making it the longest-lived rift zone eruption of the last two centuries.

Here is a look below the surface of Kilauea’s caldera (main crater) and related volcanic activity at Puʻu ʻŌʻō. The main magma chamber of Kilauea is below the caldera and scientists think there is a channel of magma that extends out from the main chamber, through the side of the volcano. Recently magma beneath Puʻu ʻŌʻō. flowed through another channel beneath the surface and started erupting closer to the ocean in Leilani Estates. Photo Credit: USGS

In March, 2018, tiltmeters, which measure changes in slope like a carpenter’s level, were showing that Puʻu ʻŌʻō was rapidly swelling and inflating. Additionally, the lava lake which sits inside the crater of Puʻu ʻŌʻō, began overflowing, generating lava flows across the surface. The pressure inside the crater built for weeks and on April 30, 2018, the crater floor collapsed and the lava lake dropped. This caused the magma under the East Rift Zone to move and push aside the fractured rocks generating a pattern of earthquakes called harmonic tremors, which can be a major warning sign that an eruption will soon occur. Pressure was growing inside the volcano, but scientists did not know when or where it would erupt.

Finally, on May 3, cracks within the surface of the Earth that formed the day before began spewing lava into Leilani Estates, a residential subdivision within the East Rift Zone on the southeastern side of the Big Island. Magma is more likely to erupt through the cracked or fractured crust as it provides an easier pathway to the surface. The next day there was a magnitude 6.9 earthquake just 10 mi from Leilani Estates, the strongest earthquake to hit Hawaii since 1975 and was felt as far away as the island of Kauai. This earthquake and the ones that followed are a result of the ongoing movement of magma in Kilauea’s East Rift Zone.

As of May 21, a total of 23 fissures (cracks) opened, around 40 structures have been destroyed, and more than 117 acres of land have been covered by lava flows. These eruptions have caused over 2000 residents to flee their homes with only one injury. A couple of the lava flows have now made their way to the ocean. The homemade videos and pictures of the lava flowing over homes, roads, and other human structures went viral.

Top Left: Several new, small cracks were seen on roads around Leilani Estates as a result of magma intruding under the surface (Photo Credit: USGS). Top Right: Cracks in the roads started steaming as magma got closer to the surface (Photo Credit: USGS). Bottom: Eventually, magma erupted through the cracks. Once magma reaches the surface, it is called lava. The flow shown here is called “AA lava” moves slower due lower temperatures and gas content. (Photo Credit: USGS).

On May 17, an explosive eruption at Kilauea sent ash clouds 30,000 ft into the air; a separate eruption from the lava flow in Leilani Estates. The lava lake at Kilauea’s main crater was also overflowing and had been dropping since the Puʻu ʻŌʻō crater floor collapsed. The lava lake dropped so low that groundwater could flow into the vent. The magma heated the water, creating steam and causing the explosion. Since then, there have been additional explosions at Kilauea and scientists continue to monitor the volcano’s activity.

Global Impacts

Hawaii offers a natural laboratory to study volcanism in both the past and present as the tectonic plate moves over the hotspot. With Kilauea being one of the most active volcanoes in the world and has been continuously erupting since 1983, scientists are able to study how volcanism evolves over time such that they can better understand volcanic processes and hazards. This is extremely helpful in developing ways to predict volcanic eruptions more accurately, so as to prevent casualties and minimize damage by providing ample warning and allowing for timely evacuations.

Map of the recent Kilauea eruptions through cracks in the earth (fissure eruptions). Photo Credit: USGS

By monitoring a volcano’s activity through changes in its slopes, seismicity, or even gas emissions and surface temperatures, scientists can learn when new magma is rising in a volcano that could eventually lead to an eruption. While scientists have had their success in predicting some eruptions, they still missed the devastating 1980 Mount St. Helens eruption. More progress is certainly needed to accurately predict when a volcano may erupt, highlighting the importance of studying the behavior of volcanoes.

 

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