Tectonic plates

It’s rare to feel earthquakes in the U.S. Northeast, so the magnitude 4.8 earthquake in New Jersey that shook buildings in New York City and was felt from Maryland to Boston on April 5, 2024, drew a lot of questions. It was one of the strongest earthquakes on record in New Jersey, though there were few reports of damage. A smaller, magnitude 3.8 earthquake and several other smaller aftershocks rattled the region a few hours later. We asked geoscientist Gary Solar to explain what causes earthquakes in this region. What causes earthquakes like this in the US Northeast? There are many ancient faults in that part of New Jersey that extend through Philadelphia and along the Appalachians, and the other direction, past New York City and into western New England. These are fractures where gravity can cause the rock on either side to slip, causing the ground to shake. There is no active tectonic plate motion in the area today, but there was about 250 million to 300 million years a...

Lava erupted through a fissure in Iceland’s Reykjanes Peninsula on Dec. 18, 2023, shooting almost 100 feet (30 meters) in the air in its early hours. Icelanders had been anticipating an eruption in the area for weeks, ever since a swarm of thousands of small earthquakes began on Oct. 23 northeast of the fishing town of Grindavík, signaling volcanic activity below. In the days that followed those first rumblings, a series of small rifts opened under the town, breaking streets, rupturing utility lines and tilting houses. GPS stations detected the ground sinking and rising over a large area. Geologists from the Icelandic Met Office interpreted the events as evidence that a basalt dike – pressurized magma that forces its way into a fracture – had intruded under Grindavík. The activity there had tapered off by early December, but 2.5 miles (4 kilometers) north of town, the ground under the Svartsengi geothermal power plant was moving....

Thousands of earthquakes in recent weeks have shaken the Icelandic fishing town of Grindavík, about 30 miles (50 kilometers) southwest of the capital Reykjavik. They have triggered evacuations and warnings that a volcanic eruption may be imminent. While the idea of magma rising was no doubt scary for tourists visiting the nearby Blue Lagoon geothermal spa, which was closed as a precaution, Iceland’s residents have learned over centuries to live with their island’s overactive geology. So, why is Iceland so volcanically active? The answer has two parts: One has to do with what geologists unimaginatively call a hotspot, and the other involves giant tectonic plates that are pulling apart right beneath the island. As a geologist, I study both. Eruptions in this region of Iceland tend to flow rather than being explosive, as residents saw in July 2023 and in 2021-22. Kristinn Magnusson/AFP via Getty Images...

Hawaii’s Mauna Loa, the world’s largest active volcano, began sending up fountains of glowing rock and spilling lava from fissures as its first eruption in nearly four decades began on Nov. 27, 2022. Where does that molten rock come from? We asked Gabi Laske, a geophysicist at the University of California-San Diego who led one of the first projects to map the deep plumbing that feeds the Hawaiian Islands’ volcanoes, to explain. Where is the magma surfacing at Mauna Loa coming from? The magma that comes out of Mauna Loa comes from a series of magma chambers found between about 1 and 25 miles (2 and 40 km) below the surface. These magma chambers are only temporary storage places with magma and gases, and are not where the magma originally came from. The origin is much deeper in Earth’s mantle, perhaps more than 620 miles (1,000 km) deep. Some scientists even postulate that the magma comes from a depth of 1,800 miles (2,900 km), where the mantle meets...