Tectonic Estuary Example — Reading Comprehension

A tectonic estuary is a type of estuary formed when movements of Earth’s crust cause land to sink. This sinking, called subsidence, creates a basin that later fills with seawater and freshwater from rivers. These estuaries often have deep waters compared to other estuaries.

One of the best-known examples of a tectonic estuary is the San Francisco Bay in California. Millions of years ago, movements along the San Andreas Fault caused parts of the land to sink. Over time, rivers like the Sacramento and San Joaquin flowed into this low area, mixing with saltwater from the Pacific Ocean. Today, San Francisco Bay is a thriving estuary that supports people, wildlife, and industries.

Tectonic estuaries have unique characteristics:

• They are usually deeper than coastal plain or bar-built estuaries.
• They are formed by powerful forces within Earth, not just by water or sand.
• They often provide safe harbors for ships because of their depth.
• They support diverse ecosystems, including fish, birds, and marine mammals.

San Francisco Bay, for example, is home to seals, sea lions, and over 500 species of fish and birds. Marshes and wetlands around the bay filter water, protect the shoreline, and provide habitat. The bay also plays an important role in California’s economy, supporting shipping, fishing, and recreation.

However, tectonic estuaries face challenges. Pollution, habitat loss, and rising sea levels threaten their health. Protecting them is important for both people and wildlife.

Fun Fact: San Francisco Bay is so large that it covers about 1,600 square miles, making it the biggest estuary on the U.S. West Coast!

What creates tectonic estuaries?

San Francisco Bay is formed by?

What rivers feed San Francisco Bay?

Why are tectonic estuaries deep?

Which animals live in San Francisco Bay?

How do wetlands help the bay?

What human use is supported?

Largest estuary on U.S. West Coast?