Science

History

Art &
Literature


GIS &
Mapping


Library

ChatRoom
Search
TrailHead
Base Camp
                                   






Geology Introduction

What is Geology?

Geology is the study if the rock formations on the earth and the forces that form them and transform them over hundreds of thousands of years - and sometimes, in a matter of minutes.
Mountains, islands, valleys and all of the earth's surface - deserts, wind caves, and volcanic craters - these are the results of geologic forces at work in and on the earth.
What are Geologic Forces?

The rock formations on the earth and the California Backcountry have been shaped by geologic forces:

Volcanoes
Earthquakes
Plate tectonics
Uplift
Glaciation


Volcanoes Volcanoes are eruptions of hot molten lava and ash that rises from deep beneath the earth's crust. Under tremendous pressure, the lava bursts up through the crust of the earth and pours boiling magma over the earth's surface.

Sometimes a volcanic eruption is sudden, massive, and spews deadly gases, ash, hot rocks, and molten lava up into the sky ... and it then falls down upon the earth destroying life on the earth's surface for miles in all directions. Entire mountains and islands can disappear in such an explosion, having been blasted by an eruption that changes the face of the earth forever.

Other times the magma creeps out of a fissure, slowly marches downhill, and adds new slowly cooling rocks and minerals to the surface, increasing the outer crust. These slow eruptions can wipe out neighborhoods, and endanger plant and animal life, but they also move slowly enough to actually watch the cooling lava move forwards across the land.

In California, the Channel Islands are directly the result of volcanic eruptions. Mount Lassen is an extinct volcano in Northern California, and the Sierra Nevada has had volcanic activity. Hawaii is an example reminding us of still-active volcanic activity, much like California was many thousands of years ago.

Earth Quakes and Plate Tectonics
Earthquakes are geologic events where the earth's crust shakes violently along fault lines. Faults are lines in many places around the earth - and there are many in California - where the crust is under tremendous pressure from several directions. In fact, there are 12 major plates on the earth's crust around the world that are each moving in a different direction.

Every border where these plates collide creates extreme tension on the crust, and to relieve this tension, the faults form and periodically let off pressure through earthquakes. Because the plates are each moving in different directions - and can be as big as the entire Pacific Ocean floor, or as big as an entire continent, there is no human technology that can stop their movement. But scientists have been able to identify these plates and the study of their movement is called plate tectonics.

In California, the Pacific plate is pushing its way north while the North American plate is pushing its way west. To see this in action, put your hands together, thumbs touching, back side of your hand towards you. Now, slide your left hand up slowly and push your right hand to the left against your left hand. You will feel the force of the left hand as it drags upwards, and the force of the right hand as it is pushed against the left hand. This is what makes California famous around the world as an earthquake zone - this pushing and pulling and dragging of the earth's crust in different directions and it causes what scientists have called the San Andreas Fault. Part of California, on the coastal edge, sits on the Pacific plate (your left hand), while the rest of California sits on the North American plate. So the coastal zone of California is sliding north, while the inland valley and Sierras are moving west.

Uplift As a result of combined forces - plate tectonics and volcanism - inland areas of California in the Backcountry experience massive vertical changes over many millions of years. The Sierra Nevada, for example, is being uplifted every year from its eastern side, raising the mountain range up above what was once a coastal shoreline to become the tallest mountains in California. The eastern face of the range is steeper than the western face due to the main force of the uplift originating on the eastern side, and it is tilting the mountains towards the west as it raises them up.

Glaciation Another amazing force of nature that affects our geology is glaciation. North America has been covered by dense, hard, miles of snow at different times in its past. Starting about 1 million years ago, and as recently as 600 years ago, the continent has experienced Ice Ages where the volume of ice and snow on the continent increases dramatically. During these Ice Ages, glaciers form.

Glaciers occur when snow accumulates faster than it can melt, and a massive body of snow packs down and becomes thicker and thicker, heavier and heavier, until it has the weight and mass of rock, even though it is still frozen water. Gravity then pulls this massive snow pack down to lower elevations, and as it travels, it shapes and scrapes, and fractures, and changes the surface of the earth.

There are glaciers in the Sierra Nevadas today that date back to the small Ice Age that occurred 600 years ago. The largest of these is near Big Pine and is now about 1 square mile in surface area. John Muir discovered signs of massive glaciation in Yosemite and proposed that it was glacial forces that carved that unusually valley. Meet with criticism and insults from the leading geologists of his time at first, his discoveries later came o be recognized a scientific fact.

Learning Activity

Take a Geology Quiz