When tectonic plates start to diverge, the linear feature formed is called a rift. Sometimes, the gap widens and sometimes it stops. When the gap eventually widens, it then evolves into a rift valley. Divergent boundaries that occur between oceanic plates produce mid-oceanic ridges.
In places where molten lava is able to move up and fill the gap, volcanic islands are eventually formed. Molten lava that rises eventually cools and forms part of the ocean floor.
One divergent boundary is the Mid-Atlantic Ridge, found at the bottom of the Atlantic and is the longest mountain range in the world. That’s right, the longest mountain range is hidden from our view. Imagine how astonished crew members of the HMS Challenger were when they discovered the massive rise underneath them. The Challenger expedition was dedicated to scientific discoveries the became foundations of oceanography. The Mid-Atlantic Ridge was observed by the HMS Challenger in 1872.
The record for the slowest divergent boundary in the world goes to Gakkel Ridge between the North American Plate and the Eurasian Plate in the Arctic Ocean. Its annual rate of separation is less than one centimeter – that’s about half as fast the rate your fingernails grow. Robotic submersibles belonging to the AGAVE expedition discovered microbial communities of over a dozen new species on this ridge.
Although not as common, rift valleys can also be formed on land. One example is the Basin and Range province in Nevada and Utah. The world’s largest freshwater lakes such as Siberia’s Lake Baikal and East Africa’s Lake Tanganyika are found in rift valleys.
One of the favorite natural laboratories for the study of divergent plate boundaries is Iceland. The Mid-Atlantic Ridge runs beneath Iceland and as the North American Plate moves westward while the Eurasian Plate moves eastward, Iceland will slowly be sliced in half. When water rushes in to fill the widening gap, this huge island of ice will form two smaller islands.
How far can divergent boundaries go? Well if we look at a time frame of 100 to 200 million years, we can easily spot the Atlantic Ocean. What is believed to have been a tiny inlet of water between the formerly merged Europe, Africa, and Americas has now evolved into this vast expanse of water.
You can read more about divergent boundaries here in Universe Today. Here are the links:
There’s more about it at USGS. Here are a couple of sources there:
Here are two episodes at Astronomy Cast that you might want to check out as well: