Methods and Analysis

Earthquake size, as measured by the Richter Scale is a well known, but not well understood, concept. The idea of a logarithmic earthquake magnitude scale was first developed by Charles Richter in the 1930's for measuring the size of earthquakes occurring in southern California using relatively high-frequency data from nearby seismograph stations. This magnitude scale was referred to as ML , with...

Magnitude scales, like the moment magnitude, measure the size of the earthquake at its source. An earthquake has one magnitude. The magnitude does not depend on where the measurement is made. Often, several slightly different magnitudes are reported for an earthquake. This happens because the relation between the seismic measurements and the magnitude is complex and different procedures will often...

Hot lava samples provide important information about what's going on in a volcano's magma chambers. We know from laboratory experiments that the more magnesium there is in magma, the hotter it is. Chemical analysis, therefore, provides the means not only to determine the crystallization history of lava but also to establish the temperature at which it was erupted. For example, Kilauea's 1997 lavas...

There are 161 potentially active volcanoes in the United States. According to a 2018 USGS assessment , 57 volcanoes are a high threat or very high threat to public safety. Many of these volcanoes have erupted in the recent past and will erupt again in the foreseeable future. As populations increase, areas near volcanoes are being developed and aviation routes are increasing. As a result, more...

Instruments to measure sulfur dioxide and carbon dioxide can be mounted in aircraft to determine the quantity of gas being emitted on a daily basis. Such instruments can also be used in a ground-based mode. An instrument that detects carbon dioxide can be installed on a volcano and configured to send data continuously via radio to an observatory. Sulfur dioxide in volcanic clouds can also be...

Most volcanoes provide warnings before an eruption. Magmatic eruptions involve the rise of magma toward the surface, which normally generates detectable earthquakes. It can also deform the ground surface and cause anomalous heat flow or changes in the temperature and chemistry of the groundwater and spring waters. Steam-blast eruptions, however, can occur with little or no warning as superheated...

Volcanoes are inherently beautiful places where forces of nature combine to produce awesome events and spectacular landscapes. For volcanologists, they're FUN to work on! Safety is, however, always the primary concern because volcanoes can be dangerous places. USGS scientists try hard to understand the risk inherent in any situation, then train and equip themselves with the tools and support...

The salinity of Great Salt Lake is measured by taking specific gravity and temperature measurements and comparing them to standardized values reported in a table. Specific gravity is measured in the field by testing a water sample with a device very similar to a battery or antifreeze tester. Learn more: Great Salt Lake, Utah

The National Field Manual for the Collection of Water-Quality Data (National Field Manual) provides guidelines and standard procedures for USGS personnel who collect data used to assess the quality of the Nation’s surface water and groundwater resources. The manual is published as separate chapters. Learn more: Techniques of Water-Resources Investigations Reports