This landslide in the Martinez hills occurred in the winter of 1998 -- a year of record rainfall due to the "El Nino" or warming of the eastern Pacific Ocean.

Stable Isotope Ratio Analysis of Water The stable isotope ratios of water are a "fingerprint" of the origin of the water.  The stable isotope ratio fingerprint is a reliable indicator of the source of a water because it is unchanged by most of the organic and inorganic chemical reactions in soil and rock.  It is, however, affected by evaporation – the light isotopes evaporate more readily and leave behind a water that is enriched in the heavy isotopes. The following graph illustrates the use of stable isotope ratios of water to determine the sources of water samples.  In this case a groundwater seep that damaged a house was alleged to have been caused by a water leak from an upslope swimming pool.  The stable isotope ratios definitively showed that the seep water was natural groundwater and not  swimming pool water.

Water is composed of hydrogen and oxygen (H2O).   The atoms of hydrogen and oxygen that comprise water each occur as several different isotope-specific atoms or nuclides.  A nuclide is defined by the number of protons, which defines the element, and the number of neutrons, which defines the specific isotope of that element.  The atomic weight of a nuclide is the sum of the protons and neutrons.  Most hydrogen (1H) has an atomic weight of 1 (1 proton and no neutrons).  Heavy hydrogen or deuterium (2H or D) has an atomic weight of 2 (1 proton and 1 neutron).  Most oxygen (16O) has an atomic weight of 16 (8 protons and 8 neutrons).  Heavy oxygen (18O) has an atomic weight of 18 (8 protons and 10 neutrons). Stable isotopes of water are measured as the ratios of the two most stable and abundant isotopes of each element.  The stable isotope ratio of oxygen is the ratio of 18O (0.204 percent of all oxygen) to 16O (99.796 percent of all oxygen).  Thus, the 18O/16O ratio is about 0.00204.  Similarly,  the stable isotope ratio of hydrogen is the ratio of 2H (0.015 percent of all hydrogen) to  1H (99.985 percent of all hydrogen) .  Thus, the 2H/1H ratio is about 0.015. Direct measurement of the absolute isotope ratios of elements is difficult.  Instead, the difference in stable isotope ratio of a sample is measured relative to a known reference (Vienna Standard Mean Ocean Water).  This difference is expressed using delta ( ) notation.  Because these differences are small,   values are expressed as parts per thousand (‰) differences from the reference.  For example, a positive   value of +10‰ for oxygen ( 18O =  +10‰) means that the sample is enriched in 18O by 10 parts per thousand compared to the reference.